[32] Landforms of the northwest of Iberia are important geographical phenomena in themselves, but more important than slope and elevation per se is the relation of these to the Atlantic Ocean and to the climatic regions that result from it. These mountains are a barrier to the storms from the northwest and west, and oceanic influence strongly felt on the seaward slopes is absent in the interior of the peninsula (Fig. 2). There is a great contrast between the aspect of the north and west slopes and that of the meseta lying in the rain-shadow of the crests. In describing the transition from the meseta to the northern highlands and shores one Spanish geographer said, "In crossing the mountains of León, the beech and chestnut forests, the galleries of trees along the rivers, the meadows, the arborescent ferns announce one's departure from yellow, dusty Spain of the Castilian steppe and the entry into northern, rainy, green Spain." ⁽¹⁾

The phrase "yellow, dusty Spain" recalls the scorching sun of summer as well as the aridity which is equally characteristic of the area. The meseta, denied the lenitive effects of the sea by the barrier of mountains, is continental in its climate. That is to say, there is a high annual temperature range between the means of its hottest and coldest months (an average of 33°F for stations of the north meseta) and, more than this, the diurnal range is also great. The temperature may drop to nearly zero during some winter nights -- the mean of the minima for the coldest month of the northern meseta is 12°F -- but the days are mostly bright even in winter, for cloudiness is slight and days with precipitation are few, averaging only eighty-five. Even though snow is not uncommon, falling on an average of fifteen days per year, it does not lie on the ground long, nor does much fall. The total precipitation for the months of December, January, and February is less than 4 inches (of water), on the average, at the typical stations of Valladolid and Salamanca.

In summer, the sun blazes down with hardly a cloud to obstruct its heating of the land. Days may be over 100°F (the mean of the maxima for the hottest month is 99°F), but nights cool rapidly. The persistently clear skies, allowing both heat in the daytime and counter-radiation at night, are not rain producers. During July and August, the two hottest months of the year, precipitation, on the average, is one inch at both Valladolid and Salamanca. Nor is precipitation high during any month of the year. As the Gonzalez Quijano map shows, the greater part of the northern meseta receives less than 20 inches in an average year. There is reason for this area to be called "yellow, dusty Spain."

In strong contrast to the meseta is the area of the mountain rim and the seaward slopes on the north and the northwest. There the effect of the ocean reduces the extremes and eliminates [35] drought, so that the two identifying characteristics of the meseta are entirely lacking. The temperature range between the mean of the coldest and the warmest months is moderate (under 22°F on the average), but as the diurnal range is also low, the absolute maximum and absolute minimum temperatures fall within relatively narrow limits. The searing heat of the interior is virtually unknown, as is the bitter cold of winter. Snow is hardly ever seen except on the high mountains. Of course, such boons carry their own deficiencies. The brilliant skies of the meseta are infrequent. The greenness and mildness of the Atlantic fringe is due to a high percentage of cloudiness through most of the year. The air is moist in all months (the yearly mean relative humidity of the city of Braga in the verdant Minho Province of Portugal -- 78 percent -- is higher than that of the month when the relative humidity of León is highest -- 77 percent). Precipitation is persistent and copious. Everywhere, for example, in Northwest Portugal the yearly total is over 40 inches and a large part of the Portuguese Minho receives between 40 and 80 inches. (Compare Braga's 73 inches with less than 20 inches received at Valladolid, about 200 miles away, on approximately the same parallel of latitude.) The mountain slopes record totals up to one hundred and some crests over 120 inches. ⁽²⁾
 

On the north coast and the northernmost part of the west coast, where the winds are onshore throughout the year, rainfall is considerable during all months, but south of Cape Finisterre a summer drought is recorded during the period of the most northerly extension of the Azorean high. On the coast of southern Galicia the period of relative drought is almost two months long and this increases as one goes southward into Portugal. Actually the dry summer months of North Portugal [36] and Galicia would not seem dry to an inhabitant of the interior of the peninsula. For example, at Braga during July and August there are, on the average, 1 4/10 inches and 1 inch respectively of rainfall. Compare these figures with those for the wettest months of Valladolid which record, on the average, 1 8/10 inches each. In other words, the two dry months of Braga receive nearly 2 1/2 inches of rain, whereas the two wettest months of Valladolid show slightly more than 3 1/2 inches. There is reason for Portuguese to refer fondly to the "green Minho."
 

Within Portugal itself there is another important contrast in climate, that between the rainy, green north and the "Mediterranean" south. ⁽³⁾ Whereas in the Minho the summer drought represents a brief respite in a rainy year, for the extreme south the rainy period represents an interlude in a relatively dry year. The winter rainy season of the Algarve is scarcely longer than the Minho dry season of summer. However, the transition between heavy rainfall and relative drought is not made as abruptly from north to south as it is from west to east. The transition from oceanic climate in the Portuguese Minho to meseta-type climate of Trás-os-Montes occurs in a short distance due to the mountains that separate the two provinces. The transition from oceanic, "Atlantic" climate on the north, where the storm tracks dominate through most of the year, to "Mediterranean" climate of the south, where there is a dominance through several months of the Azorean high-pressure area with subsident, calm, stable, dry air and clear skies, however, is a matter of latitude and takes place over a longer distance.
 

The climatic transition from north to south in Portugal is clearly shown by the statistical records of representative stations along the coast. Viana do Castelo, in the Minho, receives 61 inches of rainfall in a year and records two months with less than 1 6/10 inches (40 millimeters). Porto, near the mouth of the Douro River, receives 50 inches of rainfall and shows less than three months with rainfall under 1 6/10 inches. From Porto southward to Figueira da Foz there is a notable change. Figueira receives only 24 inches of rainfall and has five months with less than 1 6/10 inches each. Still farther to the south, at Lisbon, the figures are approximately the same as those for Figueira da Foz. At the extreme south, the Algarve is distinct from the rest of Mediterranean Portugal, as mountains shelter it on the north. It faces out over the sea toward Africa and its climate is actually more like that of North Africa than it is, for example, like that of Lisbon. Faro, the capital of the Algarve, receives less than 16 inches of rainfall in a normal year and records six months with less than 1 6/10 inches rainfall. On the average, Algarvian stations receive less rainfall than the average received by meseta stations of Spain.
 

Through the year, the Iberian peninsula comes under the influence of three meteorologic action centers: the Azorean high, the North Atlantic low, and the action center within the peninsula. The interior, the meseta, acts as a small continent to produce seasonal effects peculiar to itself.

During the summer, the Azorean high of the South Atlantic extends to the north, covering the latitudes of most of the peninsula -- at times even to the Bay of Biscay. At this season, Mediterranean summer, with stable air and clear, warm, dry days, blankets the south and west littorals up to southern [39] Galicia. The interior of the peninsula, isolated from the sea by mountains, is greatly heated, and becomes a low-pressure area in the midst of the great area of high pressures around it. Winds blow in toward the center of the low from all sides, but when the low is particularly pronounced in the midsummer months -- especially July and August -- little rain falls on the meseta. The winds from the south and southeast have their origin in dry Africa and absorb but little moisture in their traverse of the Mediterranean. Winds from the southwest and west, blowing in over relatively low and warm surfaces, are increasingly heated as they penetrate into the peninsula, and their moisture capacity is correspondingly increased. More significant than this, however, is the fact that the summer thermal low is relatively shallow. Above 10,000 feet the high of upper latitudes extends southward over it and establishes a condition of stability. During the rare periods when the Iberian depression spreads and joins that of Morocco, there are searing winds out of the east quarter, with temperatures well over 100°F and with a relative humidity as low as 10 per cent. ⁽⁴⁾ Only at the north and the extreme northwest do the inblowing winds yield summer rainfalls as they rise steeply over the mountains seeking the Iberian low; but rainfall occurs only on the windward side as the humid, oceanic air rises, cools, and condenses moisture. Within the mountain barrier, the meseta continues to be dry (Fig. 2), for the descending air masses show decreasing relative humidity.
 

In the winter, the Azorean high is reduced, and is replaced in the latitudes of the peninsula by the track of North Atlantic cyclones, which finally affect all of the peninsular peripheries and bring the influence of the ocean in over the land. Since from the end of November the temperatures of sea water are at their maximum in comparison with those of the air above them, conditions favor condensation. The humid masses of air [40] are carried landward by a series of cyclones, sometimes in a chain that will last for days or even weeks without perceptible break. Such warm-front rains come in the form of drizzles that may be persistent for days, through the passage of the several consecutive lows. Occasionally, there may be a fall in temperature, accompanied by quick showers, and then the dissipation of the clouds marking the passage of a cold front. Such are brief interludes. To this frontal precipitation is added, on the westward slopes, orographic rainfall -- produced when the humid masses are forced up the mountain slopes -- and snowfall on the higher crests.

Again, as during the summer period, the meseta is anomalous, for it is then linked with the great high-pressure area of Asia and Central Europe. While the littorals of both Mediterranean and Atlantic Iberia (and also the Pyrenean slopes) are rainy, the interior is dry, clear, and cold. In fact, the high pressure of the interior increases the precipitation on the peripheries, for it often blocks the entry of cyclones. At times these stagnate at the edges, bringing large amounts of rainfall to the coasts and snow on the mountains. ⁽⁵⁾

The rainfall of the interior differs seasonally from that of the border regions. It is dominantly that of spring and fall, taking place in the intermediate periods of change from one pronounced anomalous pressure condition to its opposite anomaly. These equinoctial seasons are times of unstable conditions and capricious weather, when one should be prepared for a beautiful, warm day with temperatures in the eighties to be followed by a freeze. With the onset of spring, cyclonic disturbances do not have the frequency, regularity, or duration of those of [41] winter, and they are interspersed with periods of fine and increasingly warm weather. They may be, however, periods of hazard for the farmer, because of unpredictability. Due to increasing heating of the land in March, the high of the interior is being dissipated and the low of the Mediterranean broadens, increasing the flow of air into the meseta. Rainfall increases there until May, when, with the greatly increased warmth of the surface, frequent thundershowers make this the month of maximum rainfall. By July, the Azorean high has spread over the west coast, bringing stable air and replacing the track of the North Atlantic cyclones. Autumn conditions are roughly comparable, in reverse, to those of spring. It is a season of unstable air, of unpredictability, and a secondary maximum of rainfall is recorded then for the meseta.

Throughout the year, temperatures are closely relative to oceanic exposure. Summer isotherms are roughly parallel to the ocean and closely spaced. Temperatures rise sharply inward to a maximum near the center of the meseta. The reverse is essentially true in winter, but not with the same degree of nicety; temperatures reach their minimum near the center of the peninsula. The west coast, with summer temperatures roughly homogeneous from the southern Alentejo ⁽⁶⁾ to the Minho, is somewhat differentiated in winter by the slightly lower temperatures of the Minho as compared with those of the south (Fig. 5).

The contrasts described in this chapter, first, between the [42] rainy northwest periphery and the meseta, that is, between Atlantic and continental climates, and second, between the Atlantic northwest and Mediterranean South Portugal, will be made even more obvious in the chapter on vegetation. ⁽⁷⁾

1. L. Solé Sabarís and Liopis Lladó, España, Geografía física, p. 270.

2. Orlando Ribeiro, Portugal, p. 47. Rainfall increases upward on all windward slopes -- presumably to the crests. None of these slopes is high enough to show diminution upward.

3. This contrast is expressed in the title and the text of the charming and perceptive book by Orlando Ribeiro, Portugal, o mediterráneo e o atlántico.

4. Orlando Ribeiro, Portugal, p. 44.

5. This is particularly notable in the Bay of Biscay. See Eduardo Hessinger, "La Distribución estacional de las precipitaciones en la península Ibérica y sus causas" (trans. from German by Valentín Masachs Alavedra), Estudios Geográficos, X, No. 34 (Feb., 1949), 124.

6. The Algarve, isolated by the mountains of Monchique and Caldeirão, is distinct. It is largely untouched by even such cold as may affect the Alentejo in winter. However, an occasional outbreak of cold air may take place when a deep high spreads westward from the interior. This occurred in the winter of 1953-1954, and again in 1955-1956, bringing snow to most of the littoral of Portugal and freezing weather even to the Algarve. Such cold causes great distress, as it happens rarely and there is no preparation for it.

7. The following, in addition to the works cited above, have been most useful in the study of climate: Pedro M. González Quijano, Mapa Pluviométrico de España, text and map of nine sheets; Hessinger, op. cit., 59-128; Wilhelm Semmeihack, "Beiträge zur Klimatographie von Nordspanien und Portugal," "Die Niederschlagsverhaltnisse," Archiv der Deutschen Seewarte, XXXIII, No. 2 (Hamburg, 1910), pp. 1-90; "Niederschlagskarte der Iberischen Halbinsel," Annalen der Hydrographie, LX (1932), 28-32, and map; "Temperaturkarten der Iberischen Halbinsel," ibid., pp. 327-333, with tables and maps; O Clima de Portugal especially Pts. I-V (1942-1946); H. Amorim Ferreira, Distribuição da chuva no território do continente Português, text of 14 pp. and map; E. Alt, Klimakunde von Mittel-und-Südeuropa, Vol. III, Pt. M, Handbuch der Klimatologie, ed. Koppen and R. Geiger.