Ebro river

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, image = Zaragoza shel.JPG
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, image_caption = The Ebro River in Zaragoza
, map = SpainEbroBasin.png
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, map_caption = The Ebro river basin
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, subdivision_type1 = Country
, subdivision_name1 = Spain
, subdivision_type2 = Region
, subdivision_name2 = Cantabria, Castile and León, Basque Country (autonomous community), La Rioja, Navarre, Aragon, Catalonia, Valencian Community
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, source1_location = Fontibre, Cantabria, Spain
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, mouth_location = Mediterranean Sea, Province of Tarragona, Catalonia, Spain
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, river_system = Ebro basin
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, tributaries_left = Nela, Jerea, Bayas, Zadorra, Ega, Arga, Aragón, Gállego, Cinca, Segre
, tributaries_right = Oca, Oja, Tirón, Najerilla, Iregua, Cidacos, Alhama, Jalón, Huerva, Martín, Guadalope, Matarranya
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The Ebro (Spanish and ; ca, Ebre ) is a river of the north and northeast of the Iberian Peninsula, in Spain. It rises in Cantabria and flows , almost entirely in an east-southeast direction. It flows into the Mediterranean Sea forming a delta in the Province of Tarragona, in southern Catalonia. In the Iberian peninsula, it ranks second in length after the Tagus and second in discharge volume, and drainage basin, after the Douro. It is the longest river entirely within Spain; the other two mentioned flow into Portugal. It is also the second-longest river in the Mediterranean basin, after the Nile.

The Ebro flows through many cities ( es, ciudades): Reinosa in Cantabria; Frías and Miranda de Ebro in Castile and León; Haro, Logroño, Calahorra, and Alfaro in La Rioja; Tudela in Navarre; Alagón, Utebo, and Zaragoza in Aragon; and Flix, Móra d'Ebre, Benifallet, Tivenys, Xerta, Aldover, Tortosa, and Amposta in the province of Tarragona (Catalonia).

Geography

Upper part and tributaries

The source of the river Ebro is in the Cantabrian Mountains, in Fontibre, Cantabria, from the Latin ''Fontes Iberis'', fount/source of the Ebro. Close by is a large artificial lake, ''Embalse del Ebro'', created by its damming.

The upper Ebro rushes through rocky gorges in Burgos Province. Flowing roughly eastwards it passes ''las conchas de Haro'' and begins forming a wider river valley among limestone rocks when it reaches La Rioja and Navarre. Southern tributaries rise on the nearby watershed, the Sistema Ibérico, a mountain range among those of Spain's centre. North of the headwaters is the Cantabrian mountain range (south of Bilbao and Santander). Much of the total water volume of the Ebro comes from its northern tributaries, which drain about of the southern slopes of the Pyrenees mountains, which run along the border with France.

All of Andorra's drainage basin is in the Ebro, through the Segre.

Climate

Downstream from Cantabria the climate in the Ebro basin – the valley being isolated from sea air masses by surrounding mountains – becomes Mediterrean/Atlantic influenced and continental. This implies summer/winter seasonal contrast and a rather dry climate. Summers of the Ebro Valley most often mirror those of a semiarid climate; some of them see more breaks of storms or showers, yet others are more arid bringing drought save where advanced irrigation is used.

The valley flood plains have rainfall between , with maxima in fall and spring. It is often covered with chaparral vegetation. Summers are hot and winters are cold. The dry summer season has temperatures of more than , occasionally reaching over . In winter, the temperatures often drop below . In some areas the vegetation depends heavily on moisture produced by condensation fog. It is a continental Mediterranean climate with extreme temperatures. There are many ground frosts on clear nights, and sporadic snowfalls.

Soil and geology

The natural topsoils across the plains are, outside of historically well-forested zones, thin. The subsoil being close to the surface is organically poor and quick-draining: calcareous, pebbly, stony layers. These are in places salt-rich, seeing some saltwater endorheic lagoons.

Karst geological processes shaped the landscape of layers of soluble carbonate rock of extensive limestone bedrock formed in an ancient seabed.

Flow volume

The valley expands and the Ebro's flow then becomes slower as its water volume increases, flowing across Aragon. There, larger tributaries flowing from the central Pyrenees and the Iberian System discharge large amounts of water, especially in spring during the thawing season of the mountain snow.

Ecosystems

The biomes are diverse in these Mediterranean climate zones: Mediterranean forests, woodlands, and scrub. Hinterlands are particularly distinctive on account of extensive sclerophyll shrublands known as maquis, or garrigues. The dominant species are ''Quercus coccifera'' (in drier areas) and ''Quercus ilex''. These trees form monospecific communities or communities integrated with ''Pinus'', Mediterranean buckthorns, ''Myrtus'', ''Chamaerops humilis'', junipers, '' Pistacia'', ''Rosmarinus'', ''Thymus'', and so on.

The hinterland climate becomes progressively more continental and drier, and therefore there is an end from extreme temperatures accompanied by slow-growing dwarf juniper species to unvegetated desert steppes as in "llanos de Belchite" or "Calanda desert".

The mountain vegetation is mostly coniferous forests that are drought-adapted, and hardier trees in the oak genus (''Quercus''), typically less tolerant, in the wetter highlands.

Halophiles (extremophiles as to salt) abound in zones of endorheic lagoons and their feeder creeks. Tamarix-covered, these include endemic species of bryophytes, chenopodiaceas, plumbaginaceae, ruppiaceaes, ''Carex'', lythraceaes, asteraceaes, and others. Their presence is related to the marine origin of the valley and the extensive marine deposits.

Just as it enters Catalonia, the valley narrows, and the river becomes constrained by mountain ranges, making wide bends. 3 massive dams have been built in this area: Mequinenza dam (Province of Zaragoza, 1955), Riba-roja dam (1955), and Flix dam (1948), the latter two in the province of Tarragona. In the final section of its course the river bends southwards and flows through spectacular gorges. The calcareous cliffs and high, rocky hills of the Serra de Cardó almost abut the river separating the Mediterranean coastal strip. After passing the gorges, the Ebro bends again eastwards near Tortosa before discharging in a delta on the Mediterranean Sea close to Amposta in the province of Tarragona.

The delta

The Ebro Delta ( ca, Delta de l'Ebre, links=no), in the Province of Tarragona, Catalonia, is at , or 20km² less, one of the largest wetlands of the western Mediterranean. Designated a Ramsar site