The conditions of the relief find their immediate reflection in those of the climate. A large internal mass with a temperate continental climate, surrounded by more or less extensive fringes of zones with a maritime climate, with intervals that mark fairly clear transitions: the reflection could not be more evident. Unfortunately, Spain lacks the establishment of a meteorological service capable of satisfying the needs of modern scientific investigation (few stations and poorly distributed; incomplete and not always reliable observations); we must therefore be satisfied with general indications.
According to top-engineering-schools, the meseta evidently determines the tendency towards the formation of a closed barometric regime, therefore of cyclonic and anticyclonic areas typical of the peninsula and contrasting with the minimums and maximums of the nearby areas. The resulting currents are usually ordered from the sea towards the interior in summer, and in the opposite direction in winter, but with various deviations and perturbations, in relation not only with the two marine mirrors, but also with the arrangement of the reliefs. Almost everywhere, however, there are two maximums of pressure (summer and winter), interspersed with two minimums in the intermediate seasons, during which the mesetait is the center of an area of depression between the Atlantic maximum (Madeira-Azores) and the minimum of Central Europe. In any case, the air currents deposit their humidity on the peripheral hills, and the result is a regime of net aridity for most of the peninsula.
It is traditional, from Brunhes onwards, to divide this into a humid Iberia and an arid Iberia: as regards Spain proper, the territory of the former represents just over a third (36.2%) of the total.. The boundary between the two regions runs roughly along the northern edge of the plateau, parallel to the course of the Ebro and the Cantabrians, but embracing the whole of Galicia, with two points corresponding to the westernmost overhang of the median mountain range (Extremadura). Most of Spain has rainfall of less than 500mm. per year and only beyond the limit that has just been mentioned is 1500 mm exceeded in restricted mountain areas. Of the arid Iberia, more than half (52%) remains below half a meter, and almost a quarter (19.5%) below 400 mm. However, the absolute minimums are not reached in the plateau, but along the Mediterranean coast, between Almería and C. di Palos, where rainfall varies between 100 and 170 mm. annui: therefore the driest area in Europe.
The seasonal distribution of precipitation is, of course, quite different, but summer corresponds everywhere to the least rainy period of the year. The wettest are autumn and spring, except that, while the autumn rains occur suddenly and vigorously (especially in the Mediterranean regions), we slowly pass, in this regard, from winter to the end of spring (especially along the coast. Atlantic). Also of great importance, due to its geographical consequences, is the contrast that the different regions of Spain show as regards atmospheric evaporation. In humid Iberia this is unable to eliminate if not a small part of the meteoric waters; on the contrary in the mesetaand along the Mediterranean coast there is always a more or less marked imbalance between the liquid inflow and the losses produced by evaporation, also because this is continuous and intense, the intermittent and irregular one.
On the other hand, the other essential element of the climate enters the exchange: temperature. Which also shows itself in strict dependence on the posture and relief conditions that characterize the various Spanish regions, but reacts in turn to these, determining, together with the behavior of the rains and atmospheric humidity, different possibilities for the development of life. More than the annual averages of temperatures (wholesale oscillating between 10 ° and 20 °, and therefore typical of a temperate climate), it is useful to consider the excursions of the extremes, both seasonal and daily. As it is natural to expect, the interior is removed over very large spaces from the moderating influences of the sea. These, although they manage to penetrate through the peripheral depressions, are clearly arrested by the thick marginal ridges;meseta to the oceanic variations of the coastal fringes is abrupt and resentful. Moreover, the interior sees these disharmonies accentuated by its altimetric conditions. The annual excursion, which on the Atlantic coast is around 12 °, and around 14 ° -16 ° on the Mediterranean one, exceeds 20 ° in the plateau, but, while in this there are not rarely extremes of −20 ° (- 22 ° in Albacete; −13 ° in Madrid) and over 40 ° (47 ° in Badajoz, 44 ° in Madrid), the peripheral areas instead benefit from a greater constancy of temperatures.
In fact, along the Atlantic coast, it drops below 10 ° from December to February, but summer rarely exceeds 20 °, while the humidity and nebulosity are greater than in other Spanish regions.
The Mediterranean coast is characterized above all by mild winters (one or two months at the most with temperatures below 10 °) and dry summers; its south-eastern portion, however, is affected by the convergent influences of the meseta and neighboring Africa: hence the strong insolation, the extreme aridity and the great transparency of the air typical of the coastal sector between Alicante and Almería. These conditions are attenuated in the Guadalquivir basin, where the beneficial breath of the humid oceanic winds is felt (this does not therefore have absolute maximums of about 50 °; and minimums of −4 ° in Seville); less, however, in the Aragonese depression, which, surrounded entirely by high reliefs, essentially participates in the climatic type of the plateau(in Pamplona: −17 ° and 40 °). In which, in contrast to the scarce importance of local variations (greater quantity of rainfall, less amplitude of annual and daily excursions, greater atmospheric nebulosity to the North. of the median cordillera) are, as typical elements, in addition to the general dryness and the considerable jump between the extreme temperatures (up to 30 ° in one day and 60 ° in the year), the duration and intensity of the cold winters, the relative abundance of snowfall, the long period of frost – which from December continues as a rule until to May – and the shortness, even intolerable, of the summer heat; all elements that are summed up in the well-known Madrid saying: “nine months of winter and three of hell”.
