The thermometer of the drought in Catalonia: reservoirs in the inland basins reach 80% capacity.

BarcelonaMarch was exceptionally rainy, with frequent, widespread, and abundant rainfall that pushed reservoir levels up to levels not seen in a long time. Two episodes were key to understanding this increase. The first occurred between Thursday the 6th and Sunday the 9th, with a strong easterly wind and, above all, the passage of an active front associated with the storm. Jana which left more than 100 l/m² or 150 l/m² in some cases. And the second was the Levante wind on March 18 and 19, which left between 40 l/m² and 70 l/m² in the pre-coastal and northeast parts of the country, but locally up to 100 l/m² or more in the Montseny area. Up to four very active storms brought rain to our country in succession, making this the wettest March of the century so far.

And throughout the spring, it has been raining irregularly, with showers and storms here and there. Some of the areas most affected by these rains or snowfalls—depending on the elevation—have been especially the main headwaters of the inland basins, where more than 300 l/m² accumulated in March alone. In some parts of the country, these figures were far exceeded, such as Els Ports, with over 500 l/m² between March 1 and 31, or some corners of the Montseny area, such as Santa Fe del Montseny, with over 600 l/m² in the same period, or Arbúcies (Selva) with over 400 l/m².

Water poured into the main rivers, which have seen their flows increase significantly during the spring and have caused reservoirs to already reach 80% capacity by mid-May. Since the beginning of March, the rise has been close to 50 points, a scenario unthinkable at the beginning of the year. Such a sudden increase has not been seen since the storm. GloryAnd there is still reserve snow melting at the highest points of the Pyrenees, where in March depths of more than one and a half or two meters have accumulated in many cases.

Reservoirs will continue their slow rise in the coming days thanks to the melting snow and afternoon showers falling in mountain areas. It's been almost four years—since July 2021—since reservoirs were at these levels. Furthermore, long-term forecasts indicate that the showers will continue to visit us over the coming months. The ground is moist, and any rain that falls will more easily reach the rivers. And the aquifers have also clearly improved. In short, we have reached a turning point that has led to the lifting of restrictions on this historic drought—the worst on record—which, now, we can truly say, is over. But be careful, as we must maintain responsible water consumption, as the climate crisis will bring more and worse dry spells like this one.

Reservoir data

The various episodes of rain in March, the thawing of snow, and the showers throughout the rest of the spring have caused the total reservoir capacity in the inland basins to go from 32% at the beginning of March to 80% currently, the best figure since July 2021, and this figure will increase further over the next few days, albeit gradually. It is worth remembering that last year the peak of reservoir capacity was at the end of June, at 37.1%, and in mid-October it dropped again before the DANA to 27.26%. A year ago, the historic low of this long drought was reached, with 14.41% at the beginning of March 2024. Therefore, the situation has changed radically, going from one extreme to the other.

If we look specifically at the current state of each reservoir, the spectacular rise of Sau stands out, going from being practically empty in February (6%) to over 75% after the abundant rains. It has now dropped below 70%, as water is being released from the Susqueda reservoir, which is now approaching 90%. All of this has meant that the emblematic church of Sant Romà de Sau—an icon and thermometer of the drought in our country—has gone from being completely out of water to currently having only the roof of the bell tower exposed. A sight that has not been seen for a long time. And the Darnius-Boadella reservoir has also skyrocketed in a way it hasn't seen in some time: it has gone from 17% before the rains to 76% now. Remember that at the beginning of March, there were still municipalities in Alt Empordà that were in a state of emergency.

As for the Baells reservoir, it is in an excellent state, unthinkable a year ago, completely full. More water is being released than is being received because the forecast is for more water to arrive from the melting snow. The Foix reservoir is completely full, and the Llosa del Cavall reservoir is already over 76% full, while the Sant Ponç reservoir is already at 94%. Since the historic DANA (Difference in the Watershed), the reservoirs in the south of the country have also been improving, and the March rains have boosted them again, although not as much as the others. The Riudecanyes reservoir was at 1.6% before the DANA and is now at 61%, and the Siurana reservoir, which was empty, is now over 26%. This is great news for the areas hardest hit by the drought. Also noteworthy are the large Rialb and Oliana reservoirs, which are full and have never before had so much reserve water, even though they belong to the Ebro Hydrographic Confederation. Rialb had to open its floodgates during the spring.

Here's a link to access data by reservoir, in this case also those in the Ebro basin, which are in much better condition and are already approaching 90%.

One-year evolution of reservoir recovery

This extraordinarily rainy March follows a winter in which, although some heavy rainfall fell in the northeast and in the Pyrenees and Pre-Pyrenees of Lleida, especially in February, the country as a whole saw little rain and was dry, even in the main headwaters of the inland basins. This left reservoirs at 31% capacity in February, a cumulative decline of four points for more than two months. Despite these figures, it's worth noting that these are double the number of reserves compared to the end of last winter; therefore, the situation had clearly improved year-on-year.

Previously, autumn concluded with the wettest October in Catalonia since 2018, and the icing on the cake was the historic and tragic DANA (Dana), which brought downpours and heavy rainfall until early November, especially in the south of the country. Rainfall has not fallen equally across the country, as it has been more moderate in the headwaters of the main Pyrenean rivers in the inland basins. However, the rain fell heavily in the southern regions, where records of between 100 l/m2 and 400 l/m2 were achieved. This boosted the reservoirs in the area.

The round of rains before the DANA (National Rainfall Storm) was also generous, leaving 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. This very welcome rain increased river flows and significantly increased some very stagnant reserves for the first time since the summer. During September, rainfall had not been very generous in the inland basins and had been concentrated rather in the west of the country, benefiting especially the rivers and reservoirs of the Ebro Hydrographic Confederation (CHE).

All this, in a year marked by a summer that resulted in a drop of almost 8 percentage points in water reserves in the inland basins, after the peak of 37.1% and 255 hm³ reached at the end of June (much more than double that of early March). At that time, it was the best figure since early October 2022. September was a fairly rainy month in several regions and with a clearly autumnal atmosphere suddenly, but the rain did not fall equally everywhere and avoided the main inland basins.

It all began in the spring of 2024, when the tap was finally turned on and rain and snow continued to fall where it was most needed to fill most reservoirs. It was the beginning of the improvement in a drought that had just bottomed out in early March. Over 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 water passed more slowly in the south of the country. Thus, spring did indeed become spring, and the icing on the cake was the widespread rainstorm on Monday, April 29th, the wettest day in all of Catalonia at that time since November 23rd, 2021. The problem is that three years of drought had left a significant mark, and that water was insufficient.

The strong storms and rains of that spring particularly benefited the Ter-Llobregat system, which exploded. Even in mid-June, the water from the Sau River surrounded and temporarily flooded the emblematic church of Sant Romà de Sau, something that hadn't been seen for a long time. But the water didn't rise as much as it has this March, not by a long shot.

The definitive end of the drought

This graph shows the evolution of the drought over the past five years. It superimposes daily data on reservoir levels in Catalonia's inland basins and daily rainfall, setting the wettest day of the storm as 100. GloryAs can be seen, after the severe setback of recent years, the situation has improved over the past twelve months, and especially in recent weeks.

2023 was the worst year of the three droughts. According to calculations by the ARA (Argentine National Research Institute) using data from 140 Meteocat stations and taking the 2009-2020 period as a reference, 2023 closed with a 31% precipitation deficit in Catalonia, a figure much higher than the 21% in 2022 and the official 21% by Meteocat, which calculates with a different number of stations and using a much longer reference period.

By mid-November of that fateful 2023, reserves in the inland basins had already dropped 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 during the 1980s, which shows that the severity of this drought is unprecedented. A scenario that, fortunately, we can already see in the distance.

The Standard Precipitation Index (SPI) 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 going back nine months, one year, or two years. They provide a long-term view of the rainfall drought by territory. The situation has clearly improved in recent months.

All of this indicates that the drought is finally over. The full snowfall from the Pyrenees has yet to reach the reservoirs, and spring promises renewed rains. Ideally, it would be 75% of reserves in June, as this figure is considered optimal to address the lack of rainfall and increased water consumption in the summer. And it seems that this year, at last, this goal is achievable.