![HeatIsland Kanto en](https://upload.wikimedia.org/wikipedia/commons/c/ce/HeatIsland_Kanto_en.png)
An urban heat island (UHI) is an
urban
Urban means "related to a city". In that sense, the term may refer to:
* Urban area, geographical area distinct from rural areas
* Urban culture, the culture of towns and cities
Urban may also refer to:
General
* Urban (name), a list of people ...
or
metropolitan area
A metropolitan area or metro is a region that consists of a densely populated urban agglomeration and its surrounding territories sharing industries, commercial areas, transport network, infrastructures and housing. A metro area usually com ...
that is significantly warmer than its surrounding
rural area
In general, a rural area or a countryside is a geographic area that is located outside towns and cities. Typical rural areas have a low population density and small settlements. Agricultural areas and areas with forestry typically are descri ...
s due to
human activities
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due to a large and complex Human brain, brain. This has enabled the development of ad ...
. The
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
difference is usually larger at night than during the day,
and is most apparent when
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
s are weak. UHI is most noticeable during the
summer
Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, the earliest sunrise and latest sunset occurs, daylight hours are longest and dark hours are shortest, wit ...
and
winter
Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures ...
. The main cause of the UHI effect is from the modification of land surfaces.
A study has shown that heat islands can be affected by proximity to different types of land cover, so that proximity to barren land causes urban land to become hotter and proximity to vegetation makes it cooler.
Waste heat
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ...
generated by energy usage is a secondary contributor.
As a population center grows, it tends to expand its area and increase its average temperature. The term heat island is also used; the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas.
Monthly
rainfall
Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water f ...
is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of
growing season
A season is a division of the year marked by changes in weather, ecology, and the amount of daylight. The growing season is that portion of the year in which local conditions (i.e. rainfall, temperature, daylight) permit normal plant growth. Whil ...
s and decreases the occurrence of weak
tornado
A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, altho ...
es. The UHI decreases
air quality
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...
by increasing the production of pollutants such as
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
, and decreases water quality as warmer waters flow into area streams and put stress on their
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
s.
Not all cities have a distinct urban heat island, and the heat island characteristics depend strongly on the background climate of the area in which the city is located.
Effects within a city can vary significantly depending on local environmental conditions. Heat can be mitigated by tree cover and green space, which act as sources of shade and promote evaporative cooling.
Mitigation of the urban heat island effect also can be accomplished through the use of
green roof
A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage ...
s,
passive daytime radiative cooling
Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero ...
applications, and the
use of lighter-colored surfaces and less absorptive building materials in urban areas, to reflect more sunlight and absorb less heat.
Urbanization has made the
effects of climate change
The effects of climate change impact the physical environment, ecosystems and human societies. The environmental effects of climate change are broad and far-reaching. They affect the water cycle, oceans, sea and land ice (glaciers), sea level ...
worse in cities.
History
The phenomenon was first investigated and described by
Luke Howard
Luke Howard, (28 November 1772 – 21 March 1864) was a British manufacturing chemist and an amateur meteorologist with broad interests in science. His lasting contribution to science is a nomenclature system for clouds, which he proposed i ...
in the 1810s, although he was not the one to name the phenomenon. Investigations of the urban atmosphere continued throughout the nineteenth century. Between the 1920s and the 1940s, researchers in the emerging field of local climatology or
microscale meteorology Microscale meteorology or micrometeorology is the study of short-lived atmospheric phenomena smaller than mesoscale, about or less. These two branches of meteorology are sometimes grouped together as "mesoscale and microscale meteorology" (MMM) ...
in Europe, Mexico, India, Japan, and the United States pursued new methods to understand the phenomenon. In 1929, Albert Peppler used the term believed to be the first instance of an equivalent to urban heat island, "staedtischen Waermeinsel." Between 1990 and 2000, about 30 studies were published annually; by 2010, that number had increased to 100, and by 2015, it was more than 300.
Causes
![newyork heat island](https://upload.wikimedia.org/wikipedia/commons/4/43/Newyork_heat_island.jpg)
There are several causes of an urban heat island (UHI); for example, dark surfaces absorb significantly more
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
, which causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day;
materials commonly used in urban areas for pavement and roofs, such as
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
and
asphalt
Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
, have significantly different thermal bulk properties (including
heat capacity
Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K).
Heat capacity i ...
and
thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
) and surface radiative properties (
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
and
emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ...
) than the surrounding rural areas. This causes a change in the
energy budget
An energy budget is a balance sheet of energy income against expenditure. It is studied in the field of Energetics which deals with the study of energy transfer and transformation from one form to another. Calorie is the basic unit of measureme ...
of the urban area, often leading to higher temperatures than surrounding rural areas.
Another major reason is the lack of
evapotranspiration
Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...
(for example, through lack of vegetation) in urban areas.
The U.S. Forest Service found in 2018 that cities in the United States are losing 36 million trees each year. With a decreased amount of vegetation, cities also lose the shade and evaporative cooling effect of trees.
Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the "
urban canyon effect". Another effect of buildings is the blocking of wind, which also inhibits cooling by
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
and prevents pollutants from dissipating. Waste heat from automobiles, air conditioning, industry, and other sources also contributes to the UHI.
High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the radiative properties of the atmosphere.
UHI not only raises urban temperatures but also increases ozone concentrations because ozone is a
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
whose formation will accelerate with the increase of temperature.
For most cities, the difference in temperature between the urban and surrounding rural area is largest at night. While temperature difference is significant all year round, the difference is generally bigger in winter. The typical temperature difference is several degrees between the center of the city and surrounding fields. The difference in temperature between an inner city and its surrounding suburbs is frequently mentioned in weather reports, as in " downtown, in the suburbs". "The annual mean air temperature of a city with 1 million people or more can be warmer than its surroundings. In the evening, the difference can be as high as ."
The UHI can be defined as either the air temperature difference (the canopy UHI) or the surface temperature difference (surface UHI) between the urban and the rural area. These two show slightly different diurnal and seasonal variability and have different causes.
Diurnal behavior
![Urban heat island variation](https://upload.wikimedia.org/wikipedia/commons/9/91/Urban_heat_island_variation.jpg)
The
IPCC
The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) a ...
stated that "it is well-known that compared to non-urban areas urban heat islands raise night-time temperatures more than daytime temperatures."
For example,
Barcelona
Barcelona ( , , ) is a city on the coast of northeastern Spain. It is the capital and largest city of the autonomous community of Catalonia, as well as the second most populous municipality of Spain. With a population of 1.6 million within ci ...
,
Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, i ...
is cooler for daily maxima and warmer for minima than a nearby rural station. A description of the very first report of the UHI by
Luke Howard
Luke Howard, (28 November 1772 – 21 March 1864) was a British manufacturing chemist and an amateur meteorologist with broad interests in science. His lasting contribution to science is a nomenclature system for clouds, which he proposed i ...
in the late 1810s said that the urban center of London was warmer at night than the surrounding countryside by . Though the warmer air temperature within the UHI is generally most apparent at night, urban heat islands exhibit significant and somewhat paradoxical diurnal behavior. The air temperature difference between the UHI and the surrounding environment is large at night and small during the day. The opposite is true for skin temperatures of the urban landscape within the UHI.
Throughout the daytime, particularly when the skies are cloudless, urban surfaces are warmed by the absorption of
solar radiation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
. Surfaces in the urban areas tend to warm faster than those of the surrounding rural areas. By virtue of their high
heat capacities, urban surfaces act as a giant reservoir of heat energy. For example, concrete can hold roughly 2,000 times as much heat as an equivalent volume of air. As a result, the large daytime surface temperature within the UHI is easily seen via thermal remote sensing.
As is often the case with daytime heating, this warming also has the effect of generating
convective
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convect ...
winds within the urban
boundary layer
In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...
. It is theorized that, due to the atmospheric mixing that results, the air temperature perturbation within the UHI is generally minimal or nonexistent during the day, though the surface temperatures can reach extremely high levels.
At night, the situation reverses. The absence of solar heating leads to the decrease of atmospheric convection and the stabilization of urban boundary layer. If enough stabilization occurs, an
inversion layer is formed. This traps urban air near the surface, and keeping surface air warm from the still-warm urban surfaces, resulting in warmer nighttime air temperatures within the UHI. Other than the heat retention properties of urban areas, the nighttime maximum in urban canyons could also be due to the blocking of "sky view" during cooling: surfaces lose heat at night principally by radiation to the comparatively cool sky, and this is blocked by the buildings in an urban area. Radiative cooling is more dominant when wind speed is low and the sky is cloudless, and indeed the UHI is found to be largest at night in these conditions.
Seasonal behavior
![Seasonal UHI in India](https://upload.wikimedia.org/wikipedia/commons/f/f9/Seasonal_UHI_in_India.jpg)
The urban heat island temperature difference is not only usually larger at night than during the day, but also larger in winter than in summer. This is especially true in areas where snow is common, as cities tend to hold snow for shorter periods of time than surrounding rural areas (this is due to the higher insulation capacity of cities, as well as human activities such as plowing). This decreases the albedo of the city and thereby magnifies the heating effect. Higher wind speeds in rural areas, particularly in winter, can also function to make them cooler than urban areas. Regions with distinct wet and dry seasons will exhibit a larger urban heat island effect during the dry season. The
thermal time constant of moist soil is much higher than that of dry soil. As a result, moist rural soils will cool slower than dry rural soils and act to minimize the nocturnal temperature difference between urban and rural regions.
Prediction
If a city or town has a good system of taking weather observations the UHI can be measured directly. An alternative is to use a complex simulation of the location to calculate the UHI, or to use an approximate empirical method. Such models allow the UHI to be included in estimates of future temperatures rises within cities due to climate change.
Leonard O. Myrup published the first comprehensive numerical treatment to predict the effects of the urban heat island (UHI) in 1969. His paper surveys UHI and criticizes then-existing theories as being excessively qualitative. A general purpose, numerical energy budget model is described and applied to the urban atmosphere. Calculations for several special cases as well as a sensitivity analysis are presented. The model is found to predict the correct order of magnitude of the urban temperature excess. The heat island effect is found to be the net result of several competing physical processes. In general, reduced evaporation in the city center and the thermal properties of the city building and paving materials are the dominant parameters. It is suggested that such a model could be used in engineering calculations to improve the climate of existing and future cities.
Impact on animals
Ant
Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...
colonies in urban heat islands have an increased heat tolerance at no cost to cold tolerance.
Species that are good at colonizing can utilize conditions provided by urban heat islands to thrive in regions outside of their normal range. Examples of this include the
grey-headed flying fox
The grey-headed flying fox (''Pteropus poliocephalus'') is a megabat native to Australia. The species shares mainland Australia with three other members of the genus ''Pteropus'': the little red ''Pteropus scapulatus, P. scapulatus'', spectacle ...
(''Pteropus poliocephalus'') and the
common house gecko
The common house gecko (''Hemidactylus frenatus'') is a gecko native to South and Southeast Asia. It is also known as the Asian house gecko, Pacific house gecko, wall gecko, house lizard, tayoto, chipkali or moon lizard.
Most geckos are nocturn ...
(''Hemidactylus frenatus''). Grey-headed flying foxes, found in
Melbourne, Australia
Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a metropol ...
, colonized urban habitats following the increase in temperatures there. Increased temperatures, causing warmer winter conditions, made the city more similar in climate to the more northerly wildland habitat of the species.
With attempts to mitigate and manage urban heat islands, temperature changes and the availability of food and water are reduced. With temperate climates, urban heat islands will extend the growing season, therefore altering breeding strategies of inhabiting species.
This can be best observed in the effects that urban heat islands have on water temperature. With the temperature of the nearby buildings sometimes reaching an over difference from the near-surface air temperature, precipitation will warm rapidly, causing run-off into nearby streams, lakes and rivers (or other bodies of water) to provide excessive
thermal pollution
Thermal pollution, sometimes called "thermal enrichment", is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is the rise or fall in the temperature of a natural body of water caused by hum ...
. The increase in thermal pollution has the potential to increase water temperature by . This increase will cause the fish species inhabiting the body of water to undergo thermal stress and shock due to the rapid change in temperature of their habitat.
Urban heat islands caused by cities have altered the
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
process.
Selective pressures like temporal variation in food, predation and water are relaxed causing a new set of selective forces to roll out. For example, within urban habitats, insects are more abundant than in rural areas. Insects are
ectotherms
An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...
. This means that they depend on the temperature of the environment to control their body temperature, making the warmer climates of the city perfect for their ability to thrive. A study done in
Raleigh, North Carolina
Raleigh (; ) is the capital city of the state of North Carolina and the List of North Carolina county seats, seat of Wake County, North Carolina, Wake County in the United States. It is the List of municipalities in North Carolina, second-most ...
conducted on
Parthenolecanium quercifex
''Parthenolecanium'' is a genus of true bugs belonging to the family Coccidae
The Coccidae are a family of scale insects belonging to the superfamily Coccoidea. They are commonly known as soft scales, wax scales or tortoise scales. The femal ...
(oak scales), showed that this particular species preferred warmer climates and were therefore found in higher abundance in urban habitats than on
oak
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
trees in rural habitats. Over time spent living in urban habitats, they have adapted to thrive in warmer climates than in cooler ones.
The presence of non-native species is heavily dependent on the amount of human activity. An example of this can be found in the populations of
cliff swallows seen nesting under the eaves of buildings in urban habitats. They make their homes using the shelter provided by humans in the upper regions of homes, allowing for an influx in their populations due to added protection and reduced predator numbers.
Other impacts on weather and climate
Aside from the effect on temperature, UHIs can produce secondary effects on local meteorology, including the altering of local wind patterns, the development of
cloud
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may co ...
s and
fog
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
, the
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
, and the rates of precipitation. The extra heat provided by the UHI leads to greater upward motion, which can induce additional shower and thunderstorm activity. In addition, the UHI creates during the day a local low pressure area where relatively moist air from its rural surroundings converges, possibly leading to more favorable conditions for cloud formation.
Rainfall rates downwind of cities are increased between 48% and 116%. Partly as a result of this warming, monthly rainfall is about 28% greater between to downwind of cities, compared with upwind. Some cities show a total precipitation increase of 51%.
Research has been done in a few areas suggesting that metropolitan areas are less susceptible to weak tornadoes due to the turbulent mixing caused by the warmth of the urban heat island.
Using satellite images, researchers discovered that city climates have a noticeable influence on plant growing seasons up to away from a city's edges. Growing seasons in 70 cities in eastern North America were about 15 days longer in urban areas compared to rural areas outside of a city's influence.
Research in China indicates that urban heat island effect contributes to climate warming by about 30%. On the other hand, one 1999 comparison between urban and rural areas proposed that urban heat island effects have little influence on global mean temperature trends. One study concluded that cities change the climate in area 2–4 times larger than their own area. Other suggested that urban heat islands affect global climate by impacting the jet stream. Several studies have revealed increases in the severity of the effect of heat islands with the progress of climate change.
Health effects
![Atlanta thermal](https://upload.wikimedia.org/wikipedia/commons/0/0a/Atlanta_thermal.jpg)
UHIs have the potential to directly influence the health and welfare of urban residents. Within the United States alone, an average of 1,000 people die each year due to extreme heat.
As UHIs are characterized by increased temperature, they can potentially increase the magnitude and duration of
heat wave
A heat wave, or heatwave, is a period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. While definitions vary, a heat wave is usually measured relative to the usual climate in the ...
s within cities. Research has found that the mortality rate during a heat wave increases exponentially with the maximum temperature,
an effect that is exacerbated by the UHI. The number of individuals exposed to extreme temperatures is increased by the UHI-induced warming. The nighttime effect of UHIs can be particularly harmful during a heat wave, as it deprives urban residents of the cool relief found in rural areas during the night.
Research in the United States suggests that the relationship between extreme temperature and mortality varies by location. Heat is more likely to increase the risk of mortality in cities in the northern part of the country than in the southern regions of the country. For example, when
Chicago
(''City in a Garden''); I Will
, image_map =
, map_caption = Interactive Map of Chicago
, coordinates =
, coordinates_footnotes =
, subdivision_type = Country
, subdivision_name ...
,
Denver
Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
, or
New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
experience unusually hot summertime temperatures, elevated levels of illness and death are predicted. In contrast, parts of the country that are mild to hot year-round have a lower public health risk from excessive heat. Research shows that residents of southern cities, such as
Miami
Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a East Coast of the United States, coastal metropolis and the County seat, county seat of Miami-Dade County, Florida, Miami-Dade C ...
,
Tampa
Tampa () is a city on the Gulf Coast of the U.S. state of Florida. The city's borders include the north shore of Tampa Bay and the east shore of Old Tampa Bay. Tampa is the largest city in the Tampa Bay area and the seat of Hillsborough County ...
,
Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...
, and
Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
, tend to be acclimated to hot weather conditions and therefore less vulnerable to heat related deaths. However, as a whole, people in the United States appear to be adapting to hotter temperatures further north each decade, although this might be due to better infrastructure, more modern building design, and better public awareness.
Increased temperatures have been reported to cause
heat stroke
Heat stroke or heatstroke, also known as sun stroke, is a severe heat illness that results in a body temperature greater than , along with red skin, headache, dizziness, and confusion. Sweating is generally present in exertional heatstroke, ...
,
heat exhaustion Heat exhaustion is a severe form of heat illness. It is a medical emergency. Heat exhaustion is caused by the loss of water and electrolytes through sweating.
The United States Department of Labor makes the following recommendation, "Heat illness ...
,
heat syncope
Heat syncope is fainting or dizziness as a result of overheating (''syncope'' is the medical term for fainting). It is a type of heat illness. The basic symptom of heat syncope is fainting, with or without mental confusion. Heat syncope is caus ...
, and
heat cramps Heat cramps, a type of heat illness, are muscle spasms that result from loss of large amount of salt and water through exercise. Heat cramps are associated with cramping in the abdomen, arms and calves. This can be caused by inadequate consumption ...
.
[ Some studies have also looked at how severe heat stroke can lead to permanent damage to organ systems.] This damage can increase the risk of early mortality because the damage can cause severe impairment in organ function.[ Other complications of heat stroke include respiratory distress syndrome in adults and ]disseminated intravascular coagulation
Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems moving parts o ...
. Some researchers have noted that any compromise to the human body's ability to thermoregulate
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
would in theory increase risk of mortality.[ This includes illnesses that may affect a person's mobility, awareness, or behavior.][ Researchers][ have noted that individuals with cognitive health issues (e.g. depression, ]dementia
Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...
, Parkinson's disease
Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...
) are more at risk when faced with high temperatures and "need to take extra care"[ as cognitive performance has been shown to be differentially affected] by heat. People with diabetes,[ are overweight,][ have sleep deprivation,][ or have cardiovascular/cerebrovascular conditions should avoid too much heat exposure.][ Some common medications that have an effect on thermoregulation can also increase the risk of mortality. Specific examples include ]anticholinergics
Anticholinergics (anticholinergic agents) are substances that block the action of the neurotransmitter called acetylcholine (ACh) at synapses in the central and peripheral nervous system.
These agents inhibit the parasympathetic nervous system ...
,[ ]diuretics
A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics in ...
,[ ]phenothiazine
Phenothiazine, abbreviated PTZ, is an organic compound that has the formula S(C6H4)2NH and is related to the thiazine-class of heterocyclic compounds. Derivatives of phenothiazine are highly bioactive and have widespread use and rich history. T ...
s[ and ]barbiturates
Barbiturates are a class of depressant drugs that are chemically derived from barbituric acid. They are effective when used medically as anxiolytics, hypnotics, and anticonvulsants, but have physical and psychological addiction potential as ...
.[ Not only health, but heat can also affect behavior. A U.S. study suggests that heat can make people more irritable and aggressive, noting that violent crimes increased by 4.58 out of 100,000 for every one degree increase in temperature.]
A researcher found that high UHI intensity correlates with increased concentrations of air pollutants that gathered at night, which can affect the next day's air quality
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...
.[ These pollutants include ]volatile organic compounds
Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a ...
, carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:
Charge-neutral
*Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide
*Nitrogen dioxide (), nitrogen(IV) oxide
*Nitrogen trioxide (), or ni ...
, and particulate matter
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The ter ...
.[ The production of these pollutants combined with the higher temperatures in UHIs can quicken the production of ]ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
.[ Ozone at surface level is considered to be a harmful pollutant.][ Studies suggest that increased temperatures in UHIs can increase polluted days but also note that other factors (e.g. ]air pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equival ...
, cloud cover
Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds on average when observed from a particular location. Okta is the usual unit for measurement of the cloud cover. The cloud co ...
, wind speed
In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer.
Wind speed ...
) can also have an effect on pollution.[ Studies from Hong Kong have found that areas of the city with poorer outdoor urban air ventilation tended to have stronger urban heat island effects and had significantly higher all-cause mortality compared to areas with better ventilation.
The ]Centers for Disease Control and Prevention
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
notes that it "is difficult to make valid projections of heat-related illness and death under varying climate change scenarios
Climate change scenarios or socioeconomic scenarios are projections of future greenhouse gas (GHG) emissions used by analysts to assess future vulnerability to climate change. Scenarios and pathways are created by scientists to survey any long ...
" and that "heat–related deaths are preventable, as evidenced by the decline of all-cause mortality during heat events over the past 35 years". However, some studies suggest that the effects of UHIs on health may be disproportionate, since the impacts may be unevenly distributed based on a variety of factors such as age, ethnicity and socioeconomic status. This raises the possibility of health impacts from UHIs being an environmental justice
Environmental justice is a social movement to address the unfair exposure of poor and marginalized communities to harms from hazardous waste, resource extraction, and other land uses.Schlosberg, David. (2007) ''Defining Environmental Justic ...
issue.
Inequality of tree canopy cover
;Relationship between neighborhood income and tree canopy cover
In recent years, researchers have discovered a strong correlation between neighborhood income and tree canopy cover. In 2010, researchers at Auburn University and University of Southern California found that the presence of trees are "highly responsive to changes in eighborhoodincome." Low-income neighborhoods tend to have significantly fewer trees than neighborhoods with higher incomes. They described this unequal distribution of trees as a demand for "luxury," rather than "necessity." According to the study, "for every 1 percent increase in per capita income, demand for forest cover increased by 1.76 percent. But when income dropped by the same amount, demand decreased by 1.26 percent."
Trees are a necessary feature in combating most of the urban heat island effect because they reduce air temperatures by , and surface temperatures by up to . Researchers hypothesized that less-well-off neighborhoods do not have the financial resources to plant and maintain trees. Affluent
Wealth is the abundance of valuable financial assets or physical possessions which can be converted into a form that can be used for transactions. This includes the core meaning as held in the originating Old English word , which is from an I ...
neighborhoods can afford more trees, on "both public and private property." Part of this is also that wealthier homeowners and communities can afford more land, which can be kept open as green space, whereas poorer ones are often rentals, where landowners try to maximize their profit
Profit may refer to:
Business and law
* Profit (accounting), the difference between the purchase price and the costs of bringing to market
* Profit (economics), normal profit and economic profit
* Profit (real property), a nonpossessory intere ...
by putting as much density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
as possible on their land.
Inequality of Impervious Surfaces
Researchers have also noted that the spread of impervious surface
Impervious surfaces are mainly artificial structures—such as pavements (roads, sidewalks, driveways and parking lots, as well as industrial areas such as airports, ports and logistics and distribution centres, all of which use considerable p ...
s is correlated with low socioeconomic status neighborhoods across various U.S. cities and states. The presence of these materials, which include concrete, tar and asphalt, serves as a predictor of "intra-urban variation in temperature." In 2013, Jesdale et al. found that after adjusting for ecoregion
An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of l ...
s, precipitation patterns, and segregation patterns, the greatest racial/ethnic disparity in the distribution of heat risk-related land cover characteristics was between blacks and whites, suggesting an issue of environmental health equity.
Impact on nearby water bodies
UHIs also impair water quality. Hot pavement and rooftop surfaces transfer their excess heat to stormwater, which then drains into storm sewers and raises water temperatures as it is released into streams, rivers, ponds, and lakes. Additionally, increased urban water body temperatures lead to a decrease in diversity in the water. In August 2001, rains over Cedar Rapids, Iowa
Cedar Rapids () is the second-largest city in Iowa, United States and is the county seat of Linn County, Iowa, Linn County. The city lies on both banks of the Cedar River (Iowa River), Cedar River, north of Iowa City, Iowa, Iowa City and north ...
, led to a 10.5C (18.9F) rise in the nearby stream within one hour, which led to a fish kill. Since the temperature of the rain was comparatively cool, it could be attributed to the hot pavement of the city. Similar events have been documented across the American Midwest, as well as Oregon and California. Rapid temperature changes can be stressful to aquatic ecosystems. Permeable pavements may mitigate these effects by percolating water through the pavement into subsurface storage areas where it can be dissipated through absorption and evaporation.
Impact on energy usage
Another consequence of urban heat islands is the increased energy required for air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
and refrigeration
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
in cities that are in comparatively hot climates. The Heat Island Group estimates that the heat island effect costs Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...
about US$
The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...
100 million per year in energy. Conversely, those that are in cold climates such as Moscow, Russia
Moscow ( , American English, US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the Capital city, capital and List of cities and towns in Russia by population, largest city of Russia. The city stands on t ...
would have less expense for heating. However, through the implementation of heat island reduction strategies, significant annual net energy savings have been calculated for northern locations such as Chicago, Salt Lake City, and Toronto.
Mitigation
The temperature difference between urban areas and the surrounding suburban or rural areas can be as much as . Nearly 40 percent of that increase is due to the prevalence of dark roofs, with the remainder coming from dark-colored pavement and the declining presence of vegetation. The heat island effect can be counteracted slightly by using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
of the city. Relative to remedying the other sources of the problem, replacing dark roofing requires the least amount of investment for the most immediate return. A cool roof
Reflective surfaces or ground-based albedo modification (GBAM) is a solar radiation management method of enhancing the Earth's albedo (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to t ...
made from a reflective material such as vinyl reflects at least 75 percent of the sun's rays, and emit at least 70 percent of the solar radiation absorbed by the building envelope. Asphalt built-up roofs (BUR), by comparison, reflect 6 percent to 26 percent of solar radiation.
Using light-colored concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature. A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat creating warmer near-surface temperatures. Paving with light-colored concrete, in addition to replacing asphalt with light-colored concrete, communities may be able to lower average temperatures. However, research into the interaction between reflective pavements and buildings has found that, unless the nearby buildings are fitted with reflective glass, solar radiation reflected off light-colored pavements can increase building temperatures, increasing air conditioning demands.
A second option is to increase the amount of well-watered vegetation. These two options can be combined with the implementation of green roof
A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage ...
s. Green roofs are excellent insulators during the warm weather months and the plants cool the surrounding environment. Air quality is improved as the plants absorb carbon dioxide with concomitant production of oxygen. The city of New York determined that the cooling potential per area was highest for street trees, followed by living roofs, light covered surface, and open space planting. From the standpoint of cost effectiveness, light surfaces, light roofs, and curbside planting have lower costs per temperature reduction.
A hypothetical "cool communities" program in Los Angeles
Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...
has projected that urban temperatures could be reduced by approximately after planting ten million trees, reroofing five million homes, and painting one-quarter of the roads at an estimated cost of US$1 billion, giving estimated annual benefits of US$170 million from reduced air-conditioning costs and US$360 million in smog related health savings.[
Mitigation strategies include:
*White roofs: Painting rooftops white has become a common strategy to reduce the heat island effect.] In cities, there are many dark colored surfaces that absorb the heat of the sun in turn lowering the albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
of the city. White rooftops allow high solar reflectance and high solar emittance, increasing the albedo of the city or area the effect is occurring.
*Passive daytime radiative cooling: A passive daytime radiative cooling
Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zero ...
roof application can double the energy savings of a white roof, attributed to high solar reflectance and thermal emittance in the infrared window
The infrared atmospheric window refers to a region of the Infrared spectrum where there is relatively little absorption of terrestrial thermal radiation by atmospheric gases. The window plays an important role in the atmospheric greenhouse effec ...
, with the highest cooling potential in hot and dry cities such as Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
and Las Vegas
Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Vegas ...
. When installed on roofs in dense urban areas, passive daytime radiative cooling panels can significantly lower outdoor surface temperatures at the pedestrian level.
*Green roofs: Green roofs are another method of decreasing the urban heat island effect. Green roofery is the practice of having vegetation on a roof; such as having trees or a garden. The plants that are on the roof increase the albedo and decreases the urban heat island effect. This method has been studied and criticized for the fact that green roofs are affected by climatic conditions, green roof variables are hard to measure, and are very complex systems
*Planting trees in cities: Planting trees around the city can be another way of increasing albedo and decreasing the urban heat island effect. It is recommended to plant deciduous
In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...
trees because they can provide many benefits such as more shade in the summer and not blocking warmth in winter.
*Green parking lot
Green parking lots are a form of parking lot designed to be environmentally more sustainable. Many agencies and organizations have released different standards as to what will be considered a green parking lot. As an example, the Toronto guideline ...
s: Green parking lots use vegetation and surfaces other than asphalt to limit the urban heat island effect.
Mitigation policies, measures and other strategies
California legislation
Assembly Bill (AB) 32 required the California Air Resources Board to create a scoping plan. This plan is California's approach on how to carry out their goal of combating climate change by reducing greenhouse emissions by 2020 to levels from the 1990s. The scoping plan had four primary programs, advanced clean cars, cap and trade, renewables portfolio standard and low-carbon fuel standard
A low-carbon fuel standard (LCFS) is an emissions trading rule designed to reduce the average carbon intensity of transportation fuels in a given jurisdiction, as compared to conventional petroleum fuels, such as gasoline and diesel. The most comm ...
all geared toward increased energy efficiency. The plan has main strategies to reduce green house gases such as having monetary incentives, regulations and voluntary actions. Every five years the scoping plan is updated.
*The advanced clean car rules program was made to reduce tail pipe emissions. The Air Resources Board approved the program to control emissions for newer models from the year 2017 to 2025. Some of their goals by 2025 are to have more environmentally superior cars to be available in different models and different types of cars. New automobiles will emit 34 percent fewer global warming gases and 75 percent fewer smog-forming emissions. And if fully implemented consumers can save an average of $6,000 over the life of the car.
*The renewable portfolio standard mandates to increase renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
from a variety of sources such as solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
and wind. Investor-owned utilities, community choice aggregators and electric service providers are required to increase procurement
Procurement is the method of discovering and agreeing to terms and purchasing goods, Service (economics), services, or other works from an external source, often with the use of a tendering or competitive bidding process. When a government agenc ...
to 33% by 2020.
*Low carbon fuel standards is administered by the California Air Resources Board
The California Air Resources Board (CARB or ARB) is the "clean air agency" of the government of California. Established in 1967 when then-governor Ronald Reagan signed the Mulford-Carrell Act, combining the Bureau of Air Sanitation and the Motor ...
and attempts to make wider choice of cleaner fuels to Californians. Producers of petroleum-based fuels are required to reduce the carbon intensity
An emission intensity (also carbon intensity or C.I.) is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule ...
of their products to 10 percent in 2020.
*Cap and trade is designed to reduce the effects of climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
by setting a cap on greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
released into the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
. The cap will decline approximately three percent each year in 2013. The trading will create incentives to reduce the effects of climate change in California communities by reducing greenhouse gases through investments in clean technologies.
Clean Air Act
The EPA
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
has initiated several air quality requirements that help reduce ground-level ozone
Ground-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with cl ...
that leads to urban heat islands. In the Clean Air Act, one of the EPA's chief policies, there are certain regulations that are put in place to ensure the state's emissions stay below a certain level. Included in the Clean Air Act, all states must set forth a State Implementation Plan A State Implementation Plan (SIP) is a United States state plan for complying with the federal Clean Air Act (United States), Clean Air Act, administered by the United States Environmental Protection Agency, Environmental Protection Agency (EPA). Th ...
(SIP) which is designed to guarantee all states meet a central air quality standard.["Reducing Urban Heat Islands: Compendium of Strategies , Heat Island Effect , US EPA." EPA. Environmental Protection Agency, n.d. Web. 16 Apr. 2014.](_blank)
/ref>
State implementation plans and policies
*The Emerging and Voluntary Measures Policy allows a state to add unconventional forms of heat island mitigation. This can include removing pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
after it has already been emitted into air, water, or soil. These measures are not implemented into law, but they do make it possible for certain parties to voluntarily become more efficient. The purpose of this policy is for all polluting sources to follow by example and use the most successful forms of mitigation.
*The Guidance on State Implementation Plan Credits for Emissions Reductions from Electric-Sector Energy Efficiency or Renewable Energy Measures is an educational tool for states to create an up-to-date and well-organized SIP. It allows states to include plans that meet the guidelines or plans that exceed expectations. Based on the success of their SIP, some states can have their plans incorporated into other SIPs.
*The Bundled Measures Policy authorizes different factions within the state to collaborate on mitigation projects. This policy takes a more of a community-based approach by adding several groups for the purpose of multiple perspectives and inventive approaches. The Bundled Measures Policy is one method that generates co-benefits for both parties. In example, if a partaking business were to add cool roofs, there will be a reduction in greenhouse gases which is beneficial for the environment as well as the need for excess energy which is beneficial for the business.
Preventing Heat Illness and Deaths Act of 2020
Bill S.4280, introduced to the U.S. Senate in 2020, would authorize the National Integrated Heat Health Information System Interagency Committee (NIHHIS) to tackle extreme heat in the United States. Successful passage of this legislation would fund NIHHIS for five years and would instate a $100 million grant program within NIHHIS to encourage and fund urban heat mitigation projects, including those using cools roofs and pavements and those improving HVAC
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...
systems. As of July 22, 2020 the bill has not moved past introduction to Congress.
Athens green space initiative
Athens
Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...
, the capital of Greece, has undertaken initiatives to mitigate the urban heat island effect and reduce the impact of pollution from vehicles. To create green spaces that offer cooling, small unused plots of land are being reconfigured into pocket parks.
Implementation of policies
The Seattle Green Factor, a multifaceted system for urban landscaping
Landscaping refers to any activity that modifies the visible features of an area of land, including the following:
# Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with a goal o ...
, has seen much success in the mitigation of urban heat islands. The program focuses on areas that are prone to high pollution, such as business districts. There are strict guidelines for any new construction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and com ...
that exceeds roughly 20 parking spaces, and this platform helps developers physically see their levels of pollution while trying different methods of construction to figure out the most effective course of action. Seattle has correspondingly produced a "score sheet" for cities to use in their city planning.
EPA Compendium of Strategies
This compendium focuses on a variety of issues dealing with urban heat islands. They describe how urban heat islands are created, who is affected, and how people can make a difference to reduce temperature. It also shows examples of policies and voluntary actions by state and local governments to reduce the effect of urban heat islands.
Incentives
*Sacramento Municipal Utility District
The Sacramento Municipal Utility District (SMUD) is a community-owned electric utility serving Sacramento County and parts of Placer County. It is one of the ten largest publicly owned utilities in the United States, generating the bulk of its po ...
(SMUD) and the Sacramento Tree Foundation have partnered to provide the city of Sacramento shade trees for free. The program allows citizens to receive trees from four to seven feet tall. They also give them fertilizer, and delivery, all at no cost. They encourage citizens to plant their trees to benefit their home by reducing air conditioning costs. Approximately more than 450,000 shade trees have been planted in the Sacramento area.
*The Eco-Roof Incentive Program: In Canada, grants
Grant or Grants may refer to:
Places
*Grant County (disambiguation)
Australia
* Grant, Queensland, a locality in the Barcaldine Region, Queensland, Australia
United Kingdom
*Castle Grant
United States
* Grant, Alabama
*Grant, Inyo County, C ...
are distributed throughout Toronto for installing green and cool roofs on residential and commercial buildings. This will reduce usage of energy and lower green house gas emissions.
*Tree vitalize: This program is a partnership with multiple entities that focuses on helping restore tree cover in the city, it also educates citizens about the positive effects of trees on climate change and the urban heat island effect. And another goal they have is to build capacity among local governments to understand, protect and restore their urban trees. Because there is a need for educating citizens about the maintenance of trees, Treevitalize provides nine hours of classroom and field training to community residents. The classes cover a variety of topics such as tree identification, pruning, tree biology, and proper species selection.["TreeVitalize." TreeVitalize. N.p., n.d. Web. 06 Apr. 2014. (Missing url)]
Weatherization
The Weatherization Assistance Program
The Low Income Home Energy Assistance Program (LIHEAP, pronounced "lie" "heap") is a United States federal social services program first established in 1981 and funded annually through Congressional appropriations. The mission of LIHEAP is to as ...
of the U.S. Department of Energy helps low income recipients by covering their heating bills and helping the families to make their homes energy efficient. In addition, this program allows states to also use the funds to install cooling efficiency measures such as shading devices.
Outreach and education
*Tree Utah: a statewide non-profit organization
A nonprofit organization (NPO) or non-profit organisation, also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benefit, in co ...
is dedicated to educating communities about the environmental and social benefits provided by trees. They are also committed to planting thousands of trees throughout the state of Utah.
*The Lawrence Hall of Science
The Lawrence Hall of Science is a public science center in Berkeley, California that offers hands-on science exhibits, designs curriculum, aids professional development, and offers after school science resources to students of all ages. The Hall ...
at UC Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...
has a high-school level course called Global Systems Science. The course focuses on a variety of topics including climate change and the greenhouse effect.
*Th
Department of Biology at the University of Central Florida
has previously offered a course, called
Systems sustainability: socially and economically viable environmental protection
". The course is an overview of connectivity, scales and networks, and various research methods, and includes a final research article & poster presentation. It is a service-learning class (students host a service event in addition to performing research funded b
UCF Land Management & Natural Resources
and th
UCF Arboretum
. One of the ongoing research projects executed by the class is the Urban Heat Island Study, as shown in thi
presentation from August 2015
and thi
presentation from November 2015
. Research is used by campus developers to ensure efficiency an
sustainability on campus
as the campus grows in attendance and area, and the UHI effect is recognized and discussed briefly in th
UCF Urban Forestry Plan from 2015
(on page 11).
Tree protection ordinances
*A variety of local governments have implemented tree and landscape ordinances, which will help communities by providing shade during summer. Tree protection is an ordinance that does not allow someone to prune
A prune is a dried plum, most commonly from the European plum (''Prunus domestica''). Not all plum species or varieties can be dried into prunes. A prune is the firm-fleshed fruit (plum) of ''Prunus domestica'' varieties that have a high solu ...
or remove trees without a city permit. An example is the city of Glendale, California
Glendale is a city in the San Fernando Valley and Verdugo Mountains regions of Los Angeles County, California, Los Angeles County, California, United States. At the 2020 United States Census, 2020 U.S. Census the population was 196,543, up from ...
: Through the Indigenous Tree Ordinance, the city of Glendale protects the following species of trees, the California sycamore
''Platanus racemosa'' is a species of plane tree known by several common names, including California sycamore, western sycamore, California plane tree, and in North American Spanish aliso. ''Platanus racemosa'' is native to California and Baja C ...
, the coast live oak
''Quercus agrifolia'', the California live oak, or coast live oak, is a highly variable, often evergreen oak tree, a type of live oak, native to the California Floristic Province. It may be shrubby, depending on age and growing location, but is g ...
, mesa oak, valley oak, scrub oak Scrub oak is a common name for several species of small, shrubby oaks. It may refer to:
*the Chaparral plant community in California, or to one of the following species.
In California
*California scrub oak (''Quercus berberidifolia''), a widespr ...
, California bay
''Umbellularia californica'' is a large hardwood tree native to coastal forests and the Sierra foothills of California, and to coastal forests extending into Oregon. It is endemic to the California Floristic Province. It is the sole species in th ...
. Anyone who is planning on removing or trimming the trees has to obtain an indigenous tree permit. Within the permit they have to provide detailed information about the number of trees affected, trunk diameter and the health of the tree itself. They also have to submit photographs of the site, and a site plan sketch.
*Another example is the city of Berkeley
Berkeley most often refers to:
*Berkeley, California, a city in the United States
**University of California, Berkeley, a public university in Berkeley, California
* George Berkeley (1685–1753), Anglo-Irish philosopher
Berkeley may also refer ...
, California. The tree protection ordinance prohibits the removal of coast live oak
''Quercus agrifolia'', the California live oak, or coast live oak, is a highly variable, often evergreen oak tree, a type of live oak, native to the California Floristic Province. It may be shrubby, depending on age and growing location, but is g ...
trees and any excessive pruning
Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots.
The practice entails the ''targeted'' removal of diseased, damaged, dead, ...
that can cause harm to the tree is also prohibited. The only exception is if the tree is poses a danger to life or limb and danger to the property.
*The city of Visalia, California
Visalia ( ) is a city in the agricultural San Joaquin Valley of California. The population was 141,384 as per the 2020 census. Visalia is the fifth-largest city in the San Joaquin Valley, the 42nd most populous in California, and 192nd in ...
, has implemented a street tree ordinance intended to promote and regulate the planting
Sowing is the process of planting seeds. An area or object that has had seeds planted in it will be described as a sowed or sown area.
Plants which are usually sown
Among the major field crops, oats, wheat, and rye are sown, grasses and leg ...
, maintenance, and protection of street trees within the city. Their ordinance
Ordinance may refer to:
Law
* Ordinance (Belgium), a law adopted by the Brussels Parliament or the Common Community Commission
* Ordinance (India), a temporary law promulgated by the President of India on recommendation of the Union Cabinet
* ...
does not allow street trees to be altered, pruned
Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots.
The practice entails the ''targeted'' removal of diseased, damaged, dead, ...
or removed. Street trees are also protected during construction.
Co-benefits of mitigation strategies
Trees and gardens aid mental health
*A large percentage of people who live in urban area
An urban area, built-up area or urban agglomeration is a human settlement with a high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities, t ...
s have access to parks and gardens in their areas, which are probably the only connections they have with nature. A study shows that having contact with nature helps promote our health
Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiza ...
and well-being. People who had access to gardens or parks were found to be healthier than those who did not.
*Another study done investigating whether or not the viewing of natural scenery may influence the recoveries of people from undergoing surgeries, found that people who had a window with a scenic view had shorter postoperative hospital stays and fewer negative comments from nurses.
Tree planting as community building
*Los Angeles TreePeople
TreePeople is an educational and training environmental advocacy organization based in Los Angeles, California. The TreePeople organization advocates and works to support a sustainable urban ecosystems in the Greater Los Angeles area through e ...
, is an example of how tree planting
Tree-planting is the process of transplanting tree seedlings, generally for forestry, land reclamation, or landscaping purpose. It differs from the transplantation of larger trees in arboriculture, and from the lower cost but slower and less re ...
can empower a community. Tree people provides the opportunity for people to come together, build capacity, community pride and the opportunity to collaborate and network
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematics
...
with each other.
Green roofs as food production
*Growing food on rooftops could be an option for fast growing communities. Popular plants grown for food include, chives
Chives, scientific name ''Allium schoenoprasum'', is a species of flowering plant in the family Amaryllidaceae that produces edible leaves and flowers. Their close relatives include the common onions, garlic, shallot, leek, scallion, and ...
, oregano
Oregano (, ; ''Origanum vulgare'') is a species of flowering plant in the mint family Lamiaceae. It was native to the Mediterranean region, but widely naturalised elsewhere in the temperate Northern Hemisphere.
Oregano is a woody perennial pla ...
and lavender
''Lavandula'' (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found in Cape Verde and the Canary Islands, and from Europe across to northern and easte ...
these plants are suitable
Proportionality is a general principle in law which covers several separate (although related) concepts:
*The concept of proportionality is used as a criterion of fairness and justice in statutory interpretation processes, especially in consti ...
for green roofs
A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage ...
because they are evolutionarily
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
equipped for Mediterranean climate
A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...
.[Dunnett, Nigel. Small Green Roofs: Low-tech Options for Greener Living. Portland, Or.: Timber, 2011. Print.]
Green roofs and wildlife biodiversity
*Green roofs are important for wildlife
Wildlife refers to domestication, undomesticated animal species (biology), species, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introduced by humans. Wildlife was also synonymous ...
because they allow organisms to inhabit the new garden. To maximize opportunities to attract wildlife to a green roof, one must aid the garden to be as diverse as possible in the plants that are added. By planting a wide array of plants, different kinds of invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
species will be able to colonize, they will be provided with foraging
Foraging is searching for wild food resources. It affects an animal's Fitness (biology), fitness because it plays an important role in an animal's ability to survive and reproduce. Optimal foraging theory, Foraging theory is a branch of behaviora ...
sources and habitat opportunities.
Urban forests and a cleaner atmosphere
*Trees provide benefits such as absorbing carbon dioxide, and other pollutants. Trees also provide shade and reduce ozone emissions from vehicles. By having many trees, we can cool the city heat by approximately 10 degrees to 20 degrees, which will help reducing ozone and helping communities that are mostly affected by the effects of climate change and urban heat islands.
Low-impact development strategy and sponge city
*Low-impact development, sponge city
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...
, is an opportunity to technically mitigate UHI phenomenon with higher compatibilities in cool pavement
Cool pavement is a road surface that uses additives to reflect solar radiation unlike conventional dark pavement. Conventional dark pavements contribute to urban heat islands as they absorb 80–95% of sunlight and warm the local air. Cool pavemen ...
and green infrastructures. Although there are some intrinsic discrepancies among understandings of sponge city and UHI mitigation towards blue infrastructure, the osmotic pool, wet pond, and regulating pond are essential supplements to urban water bodies, performing their roles in nourishing vegetation and evaporating for cooling in UHI mitigation. Sponge city pilot projects have already provided the financial foundation for taking the UHI mitigation further. It is an attempt for people in different disciplines to synergistically think about how to mitigate UHI effects, which is conducive to the generation of holistic policies, guidelines and regulations. Furthermore, the inclusion of UHI mitigation can be a driver to public participation in sponge city construction, which can consolidate the PPP model for more funds. The weights of different authorities can also be redistributed to promote institutional transitions.
Green building programs
Voluntary green building programs have been promoting the mitigation of the heat island effect for years. For example, one of the ways for a site to earn points under the US Green Building Council's (USGBC) Leadership in Energy and Environmental Design
Leadership in Energy and Environmental Design (LEED) is a
green building certification program used worldwide. Developed by the non-profit U.S. Green Building Council (USGBC), it includes a set of rating systems for the design, construction ...
(LEED) Green Building Rating System is to take action that reduces heat islands, minimizing impacts on microclimate
A microclimate (or micro-climate) is a local set of atmospheric conditions that differ from those in the surrounding areas, often with a slight difference but sometimes with a substantial one. The term may refer to areas as small as a few squ ...
s and human and wildlife habitats. Credits associated with reflective roofing or planted roofs can help a building achieve LEED certification. Buildings also receive credits by providing shade. Similarly, The Green Building Initiative's Green Globes Green Building Initiative (GBI) is a 501(c)(3) nonprofit organization that owns and administers the Green Globes green building assessment and certification in the United States and Canada. It was established in 2004 and is headquartered in Portland ...
program awards points to sites that take measures to decrease a building's energy consumption and reduce the heat island effect. As many as 10 points may be awarded to sites with roof coverage from vegetation, highly reflective materials, or a combination of the two.
Moreover, some scholars advocate that microclimate moderation should be included to foster, or at least be harmless to, the initial goals of GB in energy consumption reduction, carbon emission reduction and indoor environmental quality. Based on this, they argue the next generation of green building should be GB-based UHI mitigation system, or ‘zero UHI impact building’, or ‘zero-heat building’ or ‘microclimate neutral building’, aiming to achieve the zero-heat impact on surrounding environments through reasonably designing and operating buildings, or depending on innovative techniques to eliminate the excessive heats, on the basis of GB's goals.
Cost analysis
Every year in the U.S. 15% of energy goes towards the air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
of buildings in these urban heat islands. According to Rosenfeld et al., "the air conditioning demand has risen 10% within the last 40 years." Home and business owners alike can benefit from building a cool community. A decrease in energy usage directly correlates to cost efficiency. Areas with substantial vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic character ...
and reflective surface materials used for roofs of houses, pavement, and roads are proven to be more effective and cost efficient.
In a case study of the Los Angeles Basin
The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east-west trending chains of mountains collectively known as the Tr ...
, simulations showed that even when trees are not strategically placed in these urban heat islands, they can still aid in minimization of pollutants and energy reduction. It is estimated that with this wide-scale implementation, the city of Los Angeles can annually save $100M with most of the savings coming from cool roofs, lighter colored pavement, and the planting of trees. With a citywide implementation, added benefits from the lowering smog-level would result in at least one billion dollars of saving per year.[
The cost efficiency of ]green roofs
A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage ...
is quite high because of several reasons. According to Carter, "A conventional roof is estimated to be $83.78/m2 while a green roof was estimated at $158.82/m2." For one, green roofs have over double the lifespan of a conventional roof, effectively decelerating the amount of roof replacements every year. In addition to roof-life, green roofs add stormwater
Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...
management reducing fees for utilities. The cost for green roofs is more in the beginning, but over a period of time, their efficiency provides financial as well as health benefits.
In Capital E Analysis' conclusions of the financial benefits of green buildings, it was determined that green roofs successfully lowered energy usage and raised health benefits. For every square foot of green roof used in one study the savings amounted to $5.80 energy-wise. There were also savings seen in the emissions, water, and maintenance categories. Overall, the savings amounted to $52.90–$71.30 on average while the cost of going green totaled -$3.00–$5.00.
Climate change
Urbanization has made the effects of climate change
The effects of climate change impact the physical environment, ecosystems and human societies. The environmental effects of climate change are broad and far-reaching. They affect the water cycle, oceans, sea and land ice (glaciers), sea level ...
worse in cities.
IPCC AR6 says:
The difference in observed warming trends between cities and their surroundings can partly be attributed to urbanization
and
Compared to present day, large implications are expected from the combination of future urban development and more frequent occurrence of extreme climate events, such as heatwaves, with more hot days and warm nights adding to heat stress in cities.
A study that investigated 13,115 cities found that extreme heat
A heat wave, or heatwave, is a period of excessively hot weather, which may be accompanied by high humidity, especially in oceanic climate countries. While definitions vary, a heat wave is usually measured relative to the usual climate in the ...
exposure of a wet bulb globe temperature
The wet-bulb globe temperature (WBGT) is a type of apparent temperature used to estimate the effect of temperature, humidity, wind speed (wind chill), and visible and infrared radiation (usually sunlight) on humans. It is used by industrial h ...
above 30 °C tripled between 1983 and 2016. It increased by ~50% when the population growth in these cities is not taken into account.
Urban cold island
The same urban area that is hotter in the day can be colder than surrounding rural areas at ground level at night, leading to a new term ''urban cold island''. Snow cover in rural areas, for example, insulates plants. This was an unexpected discovery when studying the response of plants to urban environments. The urban cold island effect takes place in the early morning because the building within cities block the sun's solar radiation, as well as the wind speed within the urban centre. Both the urban heat island and urban cold island effects are most intense at times of stable meteorological conditions. Several other studies have observed the ''urban cool island'' in semi-arid or arid regions. The reason for this phenomenon is the availability of water and vegetation in the urban region as compared to the surroundings.
See also
* Anthropogenic heat
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ( ...
* Cool roof
Reflective surfaces or ground-based albedo modification (GBAM) is a solar radiation management method of enhancing the Earth's albedo (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to t ...
* Urban climatology
Urban climatology is the study of urban climate. It is a branch of climatology that concerns interactions between urban areas and the atmosphere, the effects they have on one another, and the varying spatial and temporal scales at which these proc ...
* Urban dust dome
* Urban reforestation
Urban reforestation is the practice of planting trees, typically on a large scale, in urban environments. It sometimes includes also urban horticulture and urban farming.
* Urban thermal plume
An urban thermal plume describes rising air in the lower altitudes of the Earth's atmosphere caused by urban areas being warmer than surrounding areas. Over the past thirty years there has been increasing interest in what have been called urban he ...
* Tropical night
A tropical night is a term used in many European countries to describe days when the temperature does not fall under during the night time. This definition is in use in countries including the United Kingdom, Republic of Ireland, Spain, Sweden, ...
References
Further reading
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External links
Lawrence Berkeley National Laboratory Heat Island Group
The Surface Temperature Record and the Urban Heat Island
From RealClimate.org
UrbanHeatIslands.com
– Urban Heat islands in Canada and the world
Cool Roof and Pavement Toolkit
Global Cool Cities Alliance
Urban Heat Islands – introductory video by Science Museum of Virginia
{{DEFAULTSORT:Urban Heat Island
Climatology
Climate forcing
Urbanization
Regional climate effects