Although their frequency and intensity vary widely, no area of the Spanish territory is immune to the natural risk of drought: those with the least precipitation are the most prone and vulnerable. In the Iberian Peninsula, the differences in precipitation are very pronounced: the highest average annual precipitation in humid Spain is about 3,000 mm, the lowest (<200 mm) in Dry Spain more than fifteen times. It is clear that in this second circumference the average volume is halved, extremely serious situation, while having a less bountiful year, though felt in the first. The number of rainy days also varies widely from one observatory to the next: more than 180 in some of the Bay of Biscay, and less than 30 in the Southeast between Tiñoso and Cape Gata. It is worth remembering that the Southeast is the usual region of the prayers “prop pluvia” or “ad petendam pluviam” to ask the rain to end the drought. When looking for an absolute or relative numerical reference to describe drought, what applies to one observatory does not apply to another. The word itself begins with being polysemous and has its origins: its etymology is Latin, due to the verb “sicco”, a word with multiple meanings, one of which is “to make dry time”. “siccitas” means drought, but also drought, lack of moisture, dryness; even the style used by Cicero in this sense. The Academy defines it: “Prolonged dry air”; With the two affirmations to point out, the concept of dry air and the amplitude of duration, the characterization of the first is more complex, since the issue is not just about the absence of precipitation, but also about its insufficiency. it would be very convenient understanding weather drought Absence or reduction of precipitation in the amount and duration that will cause serious losses and difficulties in the area where precipitation occurs, even in feeding populations. It should be noted, however, that this problem is largely conditioned by the presence or absence of infrastructure: therefore, in the event of an intense and prolonged Iberian-wide drought, this famine will be felt along the Cantabrian coast with supply constraints, but not in North and South Africa. . Southeastern lands protected by the Mancomunidad de los Canales del Taibilla network. Let’s remember what the Rabasa-Phenols-Amadorio Transmission expressed by the Water Consortium (1996) means for Marina Baja; Forgotten, farther in memory than time, the restrictions of 1969 and the naval transfer to Benidorm in the fall of 1978. The incidence of forest fires is also uneven: drought accompanied by even high temperatures, the probability of burning large areas is significantly lower in tidy, well-maintained, clean and controlled forests with equal physical conditions. These brief overviews serve to show that the natural phenomenon of drought has different manifestations and perceptions from one Spanish region to another, and that the causes are not the same.
Apart from the dry and temperate oceanic climates, it is a common and deep-rooted mistake of French origin to call the rest of the Iberian Peninsula’s climates Mediterranean, mixing them with the temperate climates of the dry summer season, as a concept for the Mediterranean. more expansion and less understanding; forget or not know the dry summer is a subtropical feature, not a Mediterranean feature.; that most of them share with other planetary regions (California, central Chile, Cape South Africa, and southwestern Australia). In the Iberian Peninsula, dry summer temperate climates include inland and Atlantic-influenced climates, in addition to Mediterranean climates. True Mediterranean climates cover a coastline and pre-coastal strip around this sea, which is less than a hundred kilometers wide; It is not necessary to reach Meseta from the coast of Alicante, it is enough to get to Alto Vinalopó. continentalization, becomes quite evident with the hardening of winter. For the sake of interest now, precipitation is primarily of Atlantic origin in most of the Peninsula, in the Mediterranean on the eastern and southeastern sides. The first sector is provided almost exclusively by storms and Atlantic disturbances in the western general circulation articulated by the hot jet stream; in contrast, the rainy winds in the second part are of the eastern component and originate predominantly from the east and from the Mediterranean, grayal, with bursts of cold air in the middle and upper troposphere. Pluviometric mechanisms are not the same – the Atlantic steppes are not very active and effective in the Iberian Southeast – and the patterns of droughts and low frequency variability are different.
There is empirical evidence of an ancient and recent well-known drought duality in the Iberian Southeast: Orihuela, Viciana (1564), writes the words ‘Rain or no rain, wheat is harvested in Orihuela’; Thus, he noted, when there is no rainfall, even in drought, Vega Baja’s grain harvest can bear fruit thanks to irrigation by the bottom runoff of the Atlantic-origin Segura. On the other hand, when the regional aridity of Mediterranean roots overlaps the hydrological drought of Atlantic origin, the situation can be extremely endangered, hopeless; thus, the “year of hunger” is perfectly mentioned in the annuals of the Segura basin in 1801, when it was almost five years since the fields had not been planted due to lack of rain; Particularly dry was 1815, when “Segura crossed with dry feet” in summer and autumn. There are also contradictory examples in this century: the 2013-2014 hydrological year, which was extremely dry in the Precoastal Depression and surrounding areas, was rainy to the point where reservoir volumes in Fuensanta and Cenajo in the upper Segura sub-basin exceeded 75%. joint capacity (647 hm3); Conversely, at the beginning of the 2016-2017 hydrological year, overflowing reservoirs Guadalest and Amadorio reservoirs, other Spaniards, who often had high reserves, lacked them and were almost empty. Going no further in time, the contrast of this unusual sign, with the water availability reversal, occurred this year between the parched Iberian Southeast and the Humid Spanish lands with unusual use limitations and time constraints. tanker supply and even maritime transport (Bilbao-Bermeo).
When it comes to understanding these contradictory pluviometric manifestations, in our field it is necessary to resort to a joint assessment of two teleconnection models or low-frequency variability patterns that concern, for example, the Segura basin by sector: Oscillation from the North Atlantic to the upper sub-basin and the West Mediterranean Oscillation to the lower basin; the corresponding abbreviations are NAO (North Atlantic Oscillation) and WeMO (Western Mediterranean Oscillation). The definition of each of the above models requires an atmospheric pressure dipole. For the North Atlantic Oscillation (NAO), it is configured by the Azores Anticyclone and Iceland’s Minimum or Low values, always with normalized barometric data at sea level; as a result, the axis of the dipole is approximately meridian and covers the North Atlantic bordering Western Europe; therefore, it offers a satisfactory correlation with precipitation in the spring waters of Segura caused by the Atlantic storms responsible for the bottom runoff. When measuring the index between the Azores (Ponta Delgada) and Iceland (Akureyri), a negative NAOi is Atlantic storms have free access to the Iberian Peninsula; On the contrary, a positive value indicates the presence of generally dry and sunny weather on the Peninsula and strong and extensive high pressures that impede the passage of storms and direct them to higher latitudes. As a result, a prolonged positive NAO phase with anticyclonic weather and clear skies causes drought.
On the other hand, as Martín Vide rightly points out, the previous model is hardly visible. Correlation with precipitation on the southeastern front of the peninsula, Las Vegas Media, and Baja del Segura, for the important role that westerly winds from the east play in their precipitation. This led the aforementioned geographer and climatologist to coin and propose the concept of the Western Mediterranean Oscillation (WeMO) with excellent results. The pressure difference is calculated between Cádiz-San Fernando and Padua to form the corresponding index (WeMOi): with the dipole created by the Azores Anticyclone and the low pressure area of the Gulf of Genoa; The positive phase of WeMO is described as westerly winds, parts, land to Bajo Segura and no rain. In contrast, with a negative WeMOi from low pressures in the Bay of Cadiz and a European anticyclone, the flow has an eastward component, i.e. humid winds and rain when appropriate. With very long positive phases of both oscillations, NAO and WeMO, the result is drought, as in the Iberian Peninsula during 1993-1996, with a notable predominance of both.
Finally, it should be noted that drought is not a hindrance so that after a burning summer, The high temperature of Mediterranean waters favors their specific heat and subsequent thermal inertia, increasing and prolonging the potential risk of flooding: almost all autumn, the combination of surface mechanisms (rainy winds from the east) and altitude (pits or troughs). a type of DANA) may update the potential risk in question.
Source: Informacion
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