The thermometer of drought in Catalonia: the reservoirs of the internal basins shoot up thanks to the rains

BarcelonaThe drought can be viewed from many points of view: water reserves in reservoirs, rainfall deficit, long-term or short-term outlook, immediate future... In this piece you will find climatological and reservoir indicators to have an updated and as complete as possible view of the serious drought that Catalonia is experiencing.

Meteorological spring has arrived in style, with general and quite generous rainfall throughout the territory. The main event has been between Thursday 6th and Sunday 9th, especially with the passage of an active front associated with the Jana storm that has left between 20 and 50 l/m² in many cases. One of the areas where it has rained the most is in the headwaters of the main rivers in the internal basins of the north of the country, where in some cases more than 100 or 150 l/m² have accumulated throughout the episode.

Water is pouring into the main rivers in the internal basins, which has caused the reservoirs to rise by more than three points in just a few hours. And there is also a lot of snow reserves in anticipation of the thaw at the high altitudes of the Pyrenees, where there are thicknesses of between 30 and 50 cm of new snow. Records that have already risen and reserves are expected to continue to rise for a few days. In short, a turning point this year in the fight against drought.

All this after a winter in which, although there has been some precipitation with more attention in the northeast and in the Pyrenees and Pre-Pyrenees of Lleida, in the whole territory there has been little rain and it has been dry, also in the main headwaters of the two 3-month basins, which placed the reservoirs. Despite these data, it must be said that there are twice as many reserves as at the end of last winter, so the situation has improved.

Reservoir data

The recent rains have caused the reservoirs in the internal basins to rise from 31% to more than 34%, and this figure will increase even further in the coming days. It is worth remembering that last year the peak of reserves was at the end of June, with 37.1% (the highest figure since October 2022), and in mid-October the bottom was reached before the DANA, with 27.26%. Just a year ago, the historical low of this long drought was experienced, with 14.41% at the beginning of March. Therefore, the situation is clearly much better a year later. Right now, the entire Ter-Llobregat system is already above 35%.

If we look specifically at the current state of each reservoir, the rise of Sau stands out, which has gone from being practically empty in February (6%) to more than 11%, and will continue to rise for several days. Beyond the lack of rain in winter, the main reason for the decline was the transfer of water to its older brother, Susqueda, which is at 40%. All this has led to the ruins of the old town of Sant Romà de Sau being recently uncovered, as well as its iconic church.

As for the Baells reservoir, it is already close to 60%, the Foix reservoir at 94% and the Llosa del Cavall reservoir at 35%. Also notable is the rise in the Darnius-Boadella reservoir, one of the most affected by the drought, which has already gone from 16% to more than 22% thanks to the recent rains.

In recent months, the rise in the reservoirs in the south of the country has been notable thanks to the autumn rains. The Riudecanyes reservoir went from 1.6% to almost 24% currently, and the Siurana reservoir went from less than 1% to more than 9%. These figures have not changed, since the recent rains have not been especially abundant in these areas. The Ulldecona reservoir stands out in particular, since it went from being empty to holding a full house and opening its floodgates after the DANA, and is now still above 80%, although it is not part of any Catalan river basin. Great news for the areas most affected by the drought.

Below you have a link to access data by reservoirs, in this case also those of the Ebro basin, which are in much better condition and are already close to 70%.

Evolution of rainfall

Winter has left little water and has been drier than usual. We hope that spring does not fail and brings us the usual abundant rains, something that it is doing so far. All this after an autumn that ended with the rainiest October in Catalonia since 2018, and the icing on the cake was the historic and tragic DANA that left real showers and a lot of precipitation until the beginning of November, especially in the south of the country. It has not rained equally throughout the territory, since the precipitations have been more discreet in the headwaters of the main Pyrenean rivers in the internal basins. But the water fell with a vengeance in the southern regions, where records of between 100 l/m2 and 400 l/m2 were achieved. This caused the reservoirs in the area to shoot up. Therefore, the improvement has been clear and we continue above 30% of the reserves as a whole, but unfortunately we continue to need much more water in the internal basins.

The round of rains before the DANA was also generous and left close to 100 l/m² in some parts of the Pre-Pyrenees, while in the main rivers in the north of the country, from the headwaters to the reservoirs, the amounts ranged between 50 l/m² and 8. A very welcome water that increased the flows of the rivers and clearly increased for the first time since the summer some very stagnant reserves. During September the rainfall had not been very generous in the internal basins and had been concentrated rather in the west of the country, benefiting above all the rivers and reservoirs of the Hydrographic Confederation of the Ebro (CHE).

All this, in a year marked by a summer that ended with a drop of almost 8 points in the water reserves of the internal basins, after the peak of 37.1% and 255 hm³ reached at the end of June (much more than double that of the beginning of March). This figure, which was the best since the beginning of October 2022, is now behind us. September was a fairly rainy month in several regions and with a clear autumn atmosphere suddenly, but the rain did not fall in the same way everywhere and avoided the main internal basins.

During the spring of 2024, rain and snow did not stop falling where it was most needed to fill most of the reservoirs. Over the course of those three months, more than 400 l/m² accumulated in some headwaters of the Ter-Llobregat system and more than 300 l/m² in the Darnius-Boadella basin. Between 500 l/m² and more than 750 l/m² accumulated in the headwaters of the Ebro basin, while the water passed more lightly through the south of the country. So, overall, spring did indeed act as spring, and the icing on the cake was the general rainstorm on Monday, April 29, the wettest day in all of Catalonia since November 23, 2021. The problem is that three years of drought have left a very large mark, and that water was insufficiently solutive.

The strong storms and rains of spring especially benefited the Ter-Llobregat system, which soared. Even in mid-June, the water from Sau surrounded and temporarily flooded the emblematic church of Sant Romà de Sau, an image and thermometer of the drought in Catalonia, something that had not been seen for a long time. But the water is very low again.

This graph shows the evolution of the drought as a whole over the last two years. It superimposes the daily data on the level of the reservoirs in the internal basins of Catalonia and the daily rainfall that has fallen and sets the value of 100 as the rainiest day of the storm. Glory.

This other graph is also an extension of the first one, but in this case about how it has rained day by day during the year. The round of rains at the beginning of March was the most important since the storms of September 15, 2023. In addition, the storm at the end of April was the most important since November 23, 2021. During May and June 2023 there were no major storms, but it rained almost every day in some regions.

The standard precipitation index maps produced monthly by the Meteorological Service of Catalonia indicate by region whether it has rained more or less than expected from that date and looking back six months, one year or two years. They provide a long-term view of rainfall drought by territory. The situation has improved if you look back six months.

Is the drought hole getting bigger or are we coming out of it? In this graph, prepared by ARA from data from 86 Meteocat stations, you can see month by month whether it has rained more or less than it should. A red bar means that at the end of the month we have added a rainfall deficit and a blue bar means that it has rained more than it should and that, therefore, the drought has weakened.

The figures in l/m² are not important, because they only depend on the number of stations used, but the comparison between months does allow us to see which months tend to bring a lot of rain and, therefore, whether the fact that they have been dry has led to a greater rainfall deficit. The data for the current month are based on the rain that should fall in the whole month.

2023 was the worst year of the three droughts. According to ARA calculations based on data from 140 Meteocat stations and taking the 2009-2020 period as a reference, 2023 ended with a precipitation deficit of 31% in Catalonia, a figure much higher than the 21% of 2012 with 21% cat, which makes the calculation with a different number of stations and using a much longer reference period.

In mid-November, the reserves of the internal basins already fell even below the lowest level of 1989, the historical minimum recorded. It should be remembered that current resources such as desalination plants and reclaimed water did not exist at that time, which shows that the severity of this drought is unprecedented.

2024 started with some silly rains that, without being a big deal, did leave good records in Ponent, where January was the month with the most rain since last spring. But things got lively in March, with several showers of rain and more general snowfalls. The icing on the cake was the episode of rain at the end of April, a good blow to the drought, although there is still work to be done and a lot of rain to fall because the water deficit we are dragging is significant. Be that as it may, we are on the right track.