Spain's geography: a walled plateau whose water leaves west

How the Meseta lifts the interior

Spain accounts for five sixths of the Iberian Peninsula, and most of what it accounts for is one landform. The Meseta Central extends over some 210,000 square kilometres with Madrid near its centre, and Britannica describes it as the oldest and most complex geologic formation on the peninsula: a block of ancient Hercynian rock that stayed stable while younger sediments gathered around its edges and were later pushed up into mountain ranges. The country as a whole, islands and African cities included, covers 505,990 square kilometres, and its average altitude is about 650 metres.

The plateau is not uniform, and relief and geology divide it along different lines. The Central Sierras, running west-southwest to east-northeast, split it into a northern half and a southern half. The northern Meseta, the tablelands of Castile and León, averages about 700 metres and is really a basin ringed by mountains and drained by the Duero. The southern Meseta, the Meseta of Castile-La Mancha, lies roughly 100 metres lower and has a more broken surface, the product of heavy faulting and warping, of old volcanic activity around the Calatrava plain, and of two river systems, the Guadiana and the Tagus, separated from each other by hills.

Geologically the division runs the other way, west against east. The western half is crystalline, granite and gneiss, and it carries acidic brown earths that restrict what will grow on them. The eastern half is sedimentary, mainly clays and limestones, and its plains are the plateau's agricultural ground. La Mancha occupies the south-eastern section, and the plateau at large has long been given over to cattle and to grain, with windmills still standing in several places on the ground Cervantes put them on.

Which mountains rim the central plateau

Every side of the plateau is bordered by higher ground. The Cantabrian Mountains close it to the north, the Iberian Cordillera to the north-east and east, the Sierra Morena to the south, and the lower mountains of the Portuguese frontier and Galician Spain to the north-west. Across the neck of the peninsula the Pyrenees run some 430 kilometres from the Mediterranean to the Bay of Biscay, falling steeply on their northern side and descending in terraces to the Ebro trough in the south. In the south-east the Baetic Cordillera runs broadly parallel to the coast, more than 800 kilometres long and up to 240 kilometres wide, and merges inland with the Iberian ranges.

Two great depressions break the pattern, and both sit outside the rim. The Ebro depression in the north-east is mostly plain or plateau laid on nearly horizontal sedimentary strata, closed by the Pyrenees to the north, the Iberian ranges to the south and west and coastal hills to the east, so the river has to cut through the mountains at its eastern end to reach the Mediterranean. The Guadalquivir depression in the south-west averages only 130 metres, lies open to the sea, and ends in the marshland of Las Marismas. The wall between them and the plateau can be abrupt: the south-eastern face of the Sierra Morena drops more than 1,000 metres, almost vertically, into the Guadalquivir basin, and the Cantabrian range falls some 1,500 metres within about 30 kilometres of the coast.

The north-west behaves differently again. The Galician mountains at the end of the old Hercynian block average only about 500 metres and fall away toward a coast cut into rias, deep inlets that give the Atlantic edge of the country a shape nothing on the Mediterranean side matches.

Why the big rivers finish in Portugal

Of roughly 1,800 rivers and streams in Spain, only the Tagus is longer than 960 kilometres, and all but ninety of them run less than 96 kilometres. The long ones nearly all rise in the mountains that rim or dissect the Meseta and take the plateau's western tilt. Every major river except the Ebro drains to the Atlantic, and the three longest of those westward rivers reach it beyond the country's own edge, in Portugal, on the far side of a land border of 1,214 kilometres.

The volumes matter more than the lengths. Most Iberian rivers carry a low annual volume in an irregular regime through deep valleys and canyons, and the dominant pattern is a long summer of low water: between August and September the Guadiana usually carries less than a tenth of its average annual flow. The Ebro is the exception, holding a relatively constant 540 cubic metres per second at Tortosa because snowmelt in the high Pyrenees tops up the rain, against 143 cubic metres per second on the Douro. Britannica's account of Spanish drainage quotes the judgement that aridity rivals civil war as the chief curse of historic Spain, and the flow figures are what that judgement rests on.

One river repays the country for the geography. The Guadalquivir irrigates the Andalusian plain, and because it is navigable inland it makes Seville a river port that ocean-going ships can reach, the only inland harbour in Spain that they can. On the Mediterranean side the network is thinner, partly because it drains the driest parts of the country, and rivers such as the Júcar and the Segura keep the same long summer minimum without the volume to carry through it.

How the mountains hold the weather out

The same rim that walls the plateau also governs the weather over it. The Pyrenees and the Cantabrian ranges hold the warm, dry subtropical airstream over Spain through the summer months, while westerly winds off the North Atlantic dominate most of the year and the Saharan airstream arrives less often. Northern Spain, from Galicia to northern Catalonia, is temperate and humid: A Coruña ranges from about 9 °C in winter to 18 °C in summer with roughly 965 millimetres of rain a year.

Inland the numbers change completely. Albacete, on the southern Meseta, moves between about 4 °C in winter and 24 °C in summer on less than 380 millimetres of rain a year. Across the Meseta annual rainfall generally runs between 300 and 640 millimetres, with most of the plateau near 500, and it arrives in two unreliable seasons in spring and autumn. Summer days reach the middle and upper thirties in Celsius on the plateau while nights fall back to the high teens, and the lower Ebro basin can pass 43 °C. The semi-arid classification covers the south-eastern quarter of the country and the middle and upper Ebro valley; the zone around Almería and Murcia is classified as true desert, as are parts of the eastern Canaries.

Three named winds show up in the record because they change what a season feels like. The easterly levante can hold as many as fifteen consecutive days of dry, clear weather over the coast near the Strait of Gibraltar. The leveche brings hot, dry, dust-laden air out of the south in spring and burns the vegetation of the Levantine lowlands. The solano carries the same suffocating heat across the Andalusian plain in spring and summer. Heatwaves have grown more frequent in a country that was already hot and dry, and drought episodes have grown longer and more severe.

Where the water runs short

Water shortage is the standing threat, and the geography of it follows the climate exactly. Supply problems recur in the Júcar basin each summer. In the Segura basin scarcity has pushed household water prices up by 30%. Large stretches of the Mediterranean coast are affected by saltwater intrusion, and the south-eastern regions are the most exposed of all.

What the country does with its water explains why a shortage bites. Spain had about 38,000 square kilometres under irrigation as of 2003, and of a total freshwater withdrawal of 37.22 cubic kilometres a year as of 2002, agriculture took 68%, industry 19% and households 13%, which works out at 864 cubic metres per person per year. Arable land covered 27.18% of the country and permanent crops another 9.85% as of 2005. A farming sector on that scale, in a country where the interior rivers run at a tenth of their average through late summer, is the reason reservoirs matter as much as they do; the El Atazar dam was built near Madrid to hold the capital's supply.

The other face of an irregular regime is the flood. Rivers that run low for months arrive torrentially when they arrive at all, and the record is specific about it. The Santa Teresa flood struck Murcia on 15 October 1879. Torrential rain over Valencia between 13 and 15 October 1957 killed at least 81 people. In 1982 the Júcar broke the Tous reservoir and the flood killed 30. Britannica's account puts it plainly: flooding is always a potential hazard on a peninsula whose streams have irregular regimes and deep valleys.

Where Spain stands outside the peninsula

The country lies between 27° and 44° north and between 19° west and 5° east, and those bounds only make sense because a good deal of Spain is not on the peninsula at all. The Canary Islands sit ninety kilometres off the west coast of Africa and belong geologically to the African continent. They are volcanic, and they carry the country's highest ground: Teide, 3,715 metres on Tenerife, a peak atop El Pilón, a 150-metre cone that rises from a crater within a caldera called Las Cañadas, sixteen kilometres wide. Hot gases still vent from the summit crater and from the slopes; the last eruption of El Teide came in 1909 on the north-western flank. Teide National Park was established in 1954 and is a UNESCO World Heritage site. On Gran Canaria, Pico de las Nieves reaches 1,949 metres.

The Balearic Islands are a different kind of object. They cover about 5,000 square kilometres some 80 kilometres off the eastern coast, and they are an unsubmerged portion of the Baetic Cordillera, which is why their highest ground, about 1,400 metres in north-western Mallorca, sits close to the coast while the middle of Mallorca is a plain. Eleven major islands across the two archipelagos have their own island councils and are named individually in the constitution when it fixes Senate representation.

Then there is the African coast and one village in France. Ceuta stands at the mouth of the Strait of Gibraltar and Melilla nearer the Algerian border, both administered as autonomous cities, alongside the plazas de soberanía: the Chafarinas Islands, Alhucemas, the peninsula of Vélez de la Gomera and the islet of Perejil. Alborán, out in the sea of the same name, is run from the municipality of Almería. None of this is settled ground. Morocco claims the territory the two cities stand on, and Spain disputes British sovereignty over Gibraltar, at the southern tip of the peninsula. In the Pyrenees the Catalan village of Llívia sits entirely surrounded by France, and Pheasant Island in the River Bidasoa is held as a condominium by Spain and France together.

What lives and grows on dry ground

Nearly half of Spain carries spontaneous vegetation of one kind or another, though only a small share of that, largely in the mountains, counts as dense woodland. The bands follow the rainfall. Northern Spain has heath and deciduous oak and beech. Portuguese oak grows on the mountains of the northern Meseta and on the Iberian and Baetic cordilleras, and varied pines on the central Pyrenees, the Iberian ranges and the Central Sierras. More than half the country carries Mediterranean vegetation built around the evergreen oak and other drought-resistant plants, usually reduced to the scrub called matorral.

The dry south-east has its own economy of plants. Esparto grass grows on the steppes of La Mancha and the south-east, and an associated alfa grass supplies the paper, rope and basketry that Spain has long made from it. Poplar and eucalyptus have spread widely since the 19th century. Spain records 7,600 vascular plant species within its European territory, holds an estimated 17.804 billion trees and adds about 284 million more each year, and scored 4.23 out of 10 on the 2019 Forest Landscape Integrity Index, a measure of how heavily worked a forest is instead of how much of it there is.

The wildlife carries the same double signature of a peninsula close to Africa and cut off by the Pyrenees. Wolf and brown bear survive in the scarce wild country of the north-east; wild boar, ibex and red and fallow deer are common. More than half of the bird species of Europe have been recorded at Coto Doñana National Park at the mouth of the Guadalquivir, and the Spanish imperial eagle, the eagle owl and the buzzard nest in the high Pyrenees. Desert locusts have crossed from North Africa into southern Spain. Fifteen national parks protect a sample of all of it, ten on the mainland, one in the Balearics and four in the Canaries, and by 2016 the country held 48 biosphere reserves covering 5.5 million hectares, close to 11% of its surface.

Why almost everyone lives near the coast

A population of 48,592,909 as of 1 January 2024 gives Spain about 98 people per square kilometre, and the distribution of them is uneven in a way that maps onto the terrain. The densest areas are along the coasts, with the region around Madrid as the one large exception, and 81.6% of the population lived in urban areas as of 2023. Madrid held 3.3 million people, Barcelona 1.6 million, Valencia 790,000 and Seville 690,000 as of 2019.

Madrid is the exception that proves what the plateau does. It sits at the centre of the Meseta at the foot of the Central Sierras, whose peaks pass 2,400 metres inside the Madrid region, on ground where nothing about water or climate recommends a city of that size, and it is supplied by works such as the El Atazar dam. Every other concentration of people is on the coastal plains: narrow strips between the coastal mountains and the sea, broadest along the Gulf of Cádiz where the plain joins the Andalusian lowland and along the southern and central eastern coasts, and narrowest along the Bay of Biscay where the Cantabrian range comes down close to the shore.

Movement across the country is easier than the relief suggests. The Central Sierras are high, but several passes carry road and rail to the north-west and the north-east, so the range does not cut the two halves of the plateau apart. The Montes de Toledo and the Sierra de Guadalupe, whose peaks do not rise much above 1,500 metres, have many easy passes of their own, including the ones that link the Meseta with the Andalusian plain. What the terrain does decide is where the value sits: irrigated citrus and orchard country in the Guadalquivir valley, grain and cattle on the plateau, and the tourism and the second homes strung along the warm coasts and the islands, which is what the Spanish economy and a visit to the country are both largely built on.