Drought is a silent but constant risk. It develops slowly and, without us even realizing it, the lack of rain empties the reservoirs and subtracts moisture from the soil.
A dry cycle starts and evolves as follows:
- First, the rains are lacking (meteorological drought) and high evapotranspiration values are recorded due to the lack of cloud cover, impacting the environment (ecological drought), with reservoirs below minimum levels (hydrological drought);
- then rainfed agriculture begins to suffer its effects;
- next, there is a lack of water for irrigation (agricultural drought) and for hydroelectric production;
- Finally, if the rainfall deficit is maintained, the drought reaches the cities with water restrictions (with socioeconomic drought).
In short, droughts, unlike earthquakes, have a high frequency (this is the case in Spain), a prolonged duration (several months or even years), a considerable spatial extension and a slow implantation speed, among others. other physical characteristics.
Types of droughts
The implementation of the drought, in addition to being slow, is very discreet. It is very difficult to determine when exactly a drought begins. Your start is blurred or fragmented in a succession of different dry episodes that alternate with more or less rainy episodes.
In spatial terms, we must remember that this phenomenon is highly variable in Spain and makes it impossible to speak of a single type of drought. At least four types of drought can be distinguished in our country, depending on the geographical area affected:
- Cantabrian droughts, very infrequent;
- southern droughts, the most common;
- droughts in Catalonia, short but intense;
- and Iberian droughts, which affect practically the entire country and last for a long time.
By the duration of a drought, we can also distinguish between a dry year, when rainfall accounts for less than a third of normal for a year, and a dry sequence or great drought, when these conditions last for at least two years in a row.
Currently, the Canary Islands are experiencing a prolonged drought –during 2019, 2020, partially 2021 and, if the current trend does not change, 2022–. In the Iberian Peninsula, 2021 represents the extension of the conditions of decreased rainfall that have ended up manifesting themselves abruptly in the first weeks of this year.
The last important droughts in peninsular Spain they were developed in the early 1980s and early 1990s. Generally, when a year has more than 150 days of anticyclone, a dry cycle develops.
As examples of notable droughts in recent decades, one can cite that of the Basque Country in 1989. In December of that year, Bilbao, which suffered from water restrictions, only collected a tenth of the average rainfall for the month. During the same period, the Andalusian coast (Huelva, San Fernando and Cádiz) practically registered half of its annual averages, which gave rise to floods.
Conversely, the great drought from 1992 to 1995 in central and southern Spainwith very severe water restrictions in cities such as Seville and Cádiz, coincided with normal and even higher than average amounts of rain on the Cantabrian coast.
Both droughts can be related to the so-called North Atlantic Oscillation (NAO), constituted by the dipole of the Azores anticyclone and the low pressures of Iceland. In its positive phase, this phenomenon gives rise to prolonged periods without precipitation in much of Spain, under the protection of the anticyclone, except in the north. In its negative phase, with low pressure in the Gulf of Cádiz and an anticyclone in the British Isles and the high latitudes of the North Atlantic, the rain is generous in the center and southwest of the Iberian Peninsula.
Finally, the years 2005 and 2017 were very dry. They returned to rescue the ghost of urban restrictions in different locations in our country.
An increasingly frequent and severe phenomenon
In the peninsula, a growing trend towards greater aridity is being observed throughout the territory, particularly due to an increase in the duration of periods of drought. This situation is driven by both the decrease in precipitation and the increase in evapotranspiration.
Droughts will be more and more more frequent, more severe, longer lasting and will cover more territory. This trend could worsen in the coming decades due to global warming, according to the latest climate change projectionswhich confirm the increasingly negative balance between precipitation and evapotranspiration.
Variable drought according to the region
The situation that we are currently experiencing in Spain, as a whole, can be described as Iberian drought pre-alert conditions, which must be controlled weekly. Without forgetting that in regions such as Andalusia, Catalonia, the Canary Islands and Galicia, the drought alert has already been triggered.
We have had anticyclonic conditions for almost two months, but we still cannot speak strictly of an Iberian drought situation. The atmospheric evolution in the coming months from March to May will be decisive in establishing the more or less dry character of the current hydrological year. If the rains are scarce next spring, then we would speak of an important dry year, which could be the beginning of a long-lasting dry sequence.
The available seasonal forecasts indicate, at a non-detailed spatial scale, whether the rain in the coming months will be above, equal to or below normal or the probability that it will reach certain percentiles. These forecasts indicate that precipitation will be lower than normal in much of the Iberian Peninsula at the end of winter and spring, with the exception of its easternmost strip, where it can be practically normal.
In addition, the temperature will be higher than normal throughout the territory, with which the water shortage will be aggravated. In short, the end of this dry period is not in sight at the moment.
We are prepared?
Given these conditions, it is worth asking whether our country is prepared to face an important, long-lasting dry cycle. The answer is clear: Spain is still not prepared to face a major drought.
The situation in the peninsular interior and in the Cantabrian regions is especially delicate. The Mediterranean coast and the two archipelagos are better prepared, surely because they have suffered the effects of large dry sequences in past decades and have taken measures to avoid shortages, at least in urban areas.
The construction of desalination plants and the promotion of the reuse of purified water are key in this process. And these actions have had no effect on the Cantabrian or inland peninsular regions, so they are highly exposed to a long sequence of lack of rainfall, which would have serious effects on agriculture and livestock and would cause a more than likely shortage in many urban centers.
Spain must urgently adapt to the reality of climate change and the possibility, more than likely according to climate models, that these dry sequences will become more frequent in the coming decades. We do not have well calculated the dimensions of the urban water supply tanks for these conditions.
In short, water planning in our country must stop being based on continuous supply, because rains are going to be scarce, and must be carried out from the correct management of demand, with savings and rational use, avoiding implementing activities in the territory that involve continuous increases in the consumption of water resources (new irrigation, real estate development above the real needs of housing…).
Climate change forces us to change our way of relating to the natural environment and its elements, especially with water in our country. If we don’t, situations like the ones we are experiencing will have an increasingly greater economic, social and political cost.
This article was originally published on The Conversation. you can read here the original version.