According to the Portuguese Institute of the Sea and the Atmosphere (IPMA), a hydrological year is between October 1st and September 30th of the following year and so far, according to IPMA data, the 2021/2022 hydrological year is the second driest since 1931 (since records began), only surpassed by the hydrological year 2004/2005.
According to an official IPMA source, so far this hydrological year has had 419 millimetres (mm) of rain, 51% of what would be a normal value.
With all of mainland Portugal in drought, 55% in severe drought class and 45% in extreme drought, the IPMA considers that the drought “would have a significant amelioration” if in the next two months it rained above average. But it adds that this only happens in 20% of the years.
In average terms, in September in October, for the situation to improve, something like 150mm in September and 175mm in October.
Although it rained in the spring of this year, in some regions above average in March, according to preliminary results from the spring climate report, rainfall in the season corresponded to 80% of normal.
Worsening since last year
The drought situation of the current hydrological year had already been worsening since the autumn of last year, when the amount of precipitation in the months from September to November was 172.8 mm, which corresponded to about 69% of the average value. Last autumn, according to the IPMA, was the third driest since 2020. And the month of November was especially dry, with 90.5 mm less rain compared to the average value.
As a result of an autumn with little rain, the meteorological drought extended to almost the entire territory at the end of November and increased in intensity in the south. At the end of autumn, 92% of the mainland was in meteorological drought, that is, with a lack of rain.
In winter, according to IPMA data, the situation has not improved, the season was the fifth driest since 1931. The numbers show that the total precipitation in the months of December to February, 117.6 mm, corresponded to only 33% of the average value.
January was classified as very dry and February as extremely dry.
Adding to the lack of rain and high temperatures (the fourth warmest winter since 1931), last winter saw a worsening of the meteorological drought, which became more intense across the continent. At the end of winter, 66% of the continent was in the most severe, severe and extreme drought classes.
In addition to the high temperatures, the country has already registered two heat waves this year.
Asked by Lusa about whether this worsened the drought situation, the IPMA source explained that “the hydrological drought that the mainland faces is directly related to the persistent rainfall deficit recorded and not so much with the occurrence of heat waves”.
“Heat waves are phenomena that, in some way, are part of the climatic characterisation of the continental territory and impact the evaporation of the amount of water stored in reservoirs, dams and dams”, they added.