The only desert in Europe and one of the rainiest ranges in Spain are both in Andalusia, and the same mountains produce them

Andalusia has an image problem that is really a problem of scale. It is imagined as a uniform region of sun, whitewash and olive trees, and it is in fact the most violently contrasted climatic territory in Spain. Between its two extremes the difference in rainfall is more than ten to one, and they are 280 kilometres apart: about the distance from London to Manchester.

The interesting part is that the two extremes are not independent accidents. They are the two faces of the same obstacle.

01 Three bands and no middle ground

The physical map of Andalusia reads as three parallel bands, north to south. At the top, Sierra Morena, an old rounded step that separates it from the central plateau and never reaches 1,400 metres. In the middle, the Guadalquivir depression: a triangular plain opening towards the Gulf of Cádiz. At the bottom, the Baetic ranges, young, folded and far higher.

That third band is the one in charge. The Béticas cross the region from southwest to northeast, from the province of Cádiz to that of Almería, and work as a tilted wall facing the sea. Humid Atlantic air hits them at their western end. By the time it reaches the eastern end, it has nothing left to give up.

02 Where the Atlantic hits the wall

The western end of the Béticas stands little more than sixty kilometres from the ocean and is the first thing Atlantic fronts meet as they come in over the Gulf of Cádiz. There, in the Sierra de Grazalema, the air has to climb a thousand metres at once, cools and unloads. Annual averages pass 2,000 millimetres, and in 1963 the total reached 4,346: the highest annual figure ever recorded in mainland Spain.

The result looks nothing like most people's idea of Andalusia. There is closed forest, persistent fog and a tree that survives only here and in a handful of neighbouring ranges: the pinsapo, a fir left stranded when the climate dried out, found nowhere else in the world except northern Morocco.

It is worth being precise: Grazalema is not the wettest place in Spain — parts of Galicia and the Basque Country comfortably compete — but it is the wettest in Andalusia and among the wettest in the country. What makes it extraordinary is that it sits a hundred kilometres from a desert.

03 The other end: the rain shadow

Two hundred and eighty kilometres east, at Cabo de Gata, the same range produces the opposite effect. Whatever fronts remain have already crossed the entire barrier and arrive exhausted; the ranges of Almería then intercept them one last time. The cape's station records around 156 millimetres a year, with an annual mean of 19.8 degrees.

With those figures the climate classification stops being Mediterranean and becomes hot desert. It is the only point in Europe in that category, and also the driest on the continent. The natural park protecting it covers 460 square kilometres of volcanic hills, salt pans and coves, and its landscape resembles North Africa more than the rest of the peninsula.

Same region. Same mountain system, even. The only thing that changes is which side of the wall you are standing on.

04 A 3,479-metre roof forty kilometres from the sea

In their central stretch the Béticas peak at Sierra Nevada. Mulhacén stands 3,479 metres and is the highest summit in the Iberian Peninsula. Its prominence — the height it rises above the col linking it to any higher mountain — is 3,285 metres, the third greatest in Europe.

What makes that figure unusual is not the height but the distance. Mulhacén lies some forty kilometres from the Mediterranean in a straight line. That is three and a half thousand metres of drop across the space a large city and its suburbs occupy, and it produces two visible consequences.

The first is that Europe's southernmost ski resort operates here, with runs between 2,100 and 3,300 metres; Pradollano, at 2,100, is the highest inhabited settlement in Andalusia. The second is that at the foot of the range, sheltered from the north by that bulk, the coast of Granada has a subtropical microclimate where custard apple, avocado and mango are grown at the same latitude.

05 The valley that took the cities

Between the two ranges lies the middle band, and that is where nearly everything else sits. The Guadalquivir runs 657 kilometres from the Sierra de Cazorla to the Atlantic, opening a plain that exists nowhere else in the southern peninsula. It is fertile, it is easy to cross, and it is the only flat ground for hundreds of kilometres.

The detail almost nobody keeps in mind is that this river is navigable. Seville sits some eighty kilometres from the mouth and remains the only inland commercial port in Spain: ships come up the estuary with the tides, whose reach upstream is cut off by the Alcalá del Río dam. An inland city with seagoing cargo quays is not a common sight in Europe.

That is why the big Andalusian cities are where they are. Seville, Córdoba and Jaén line up along the valley or on its edge; Granada settles in the only wide basin inside the Béticas; Málaga, Cádiz, Huelva and Almería occupy the few gaps where the mountains leave room beside the water. The distribution is not historical. It is topographic.

06 What this changes for the traveller

The first consequence is that there is no such thing as the Andalusian climate. There is the valley's, an oven in summer and mild and damp in winter; the coast's, far more temperate all year; and the mountains', which in January carry two metres of snow. Packing for all three at once is impossible, and packing for one is the sensible move.

The second is that distances mislead in both directions. Along the valley you move fast, on flat ground and good roads. The moment you enter the Béticas the map stops working: climbing to a mountain village that appears thirty kilometres away can cost a long hour of bends.

The third is about expectation. Anyone coming for postcard Andalusia will find it without effort, but will have missed the most interesting thing: that in a single day you can go from cloud forest to desert without leaving the region, and that both are consequences of the same wall of rock. It is rare for a region so recognisable from outside to be so little of a piece within.