The thermometer of the drought in Catalonia: reservoirs in the inland basins exceed 64%.

BarcelonaThe month of March was very rainy, with frequent, widespread, and abundant rainfall that pushed reservoir levels 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.

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 have accumulated throughout March. In some parts of the country, these figures have been far exceeded, such as Els Ports, where more than 500 l/m² have fallen since March 1, or in some parts of the Montseny region, such as Arbúcies (Selva), where more than 400 l/m² have fallen.

Water is pouring into the main rivers, which have seen their flows increase significantly and have caused reservoirs to now well exceed 60%. The increase has been 30 points in just one month, doubling reserves that have gained more than 200 cubic hectometers (hm³) in just a few days. Such a sudden increase has not been seen since the storm. GloryAnd there's also plenty of reserve snow left for the thaw at the highest points of the Pyrenees, where there are depths of snow well over a meter or a meter and a half.

Reserves will continue to rise in the coming days, albeit much more slowly. In fact, reservoirs have not been at these levels for more than three years—since autumn 2021. Furthermore, long-term forecasts indicate that rainfall will continue to fall throughout the spring, with marked instability. The ground is moist, and any rain that falls will reach the rivers more easily. And the aquifers have also clearly improved. In short, we have experienced a turning point that has led to the lifting of restrictions on this historic drought—the worst on record—which, now, we can finally say, is over. But be careful, we must maintain responsible water consumption, as the climate crisis will bring more and worse dry spells like this one.

Reservoir data

The various rainy episodes in March have caused all reservoirs in the inland basins to go from almost 32% capacity in one month to over 64% capacity currently, the best figure since autumn 2021, and this figure will increase even further in the coming days, albeit gradually. It's worth remembering that last year's peak reservoir capacity was at the end of June, at 37.1%, and in mid-October it dropped again before the DANA, reaching 27.26%. Just a year ago, the historic low of this long drought was reached, with 14.41% capacity at the beginning of March 2024. Therefore, the situation has changed radically, going from one extreme to the other. As for the Ter-Llobregat system, it is already approaching 65%.

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 almost 73%. In fact, the water level has risen so much that the emblematic church of Sant Romà de Sau—an icon and thermometer of the drought in our home—has gone from being completely out of water to currently having only the roof of the bell tower exposed. A sight that hasn't been seen for a long time. Its older sister, Susqueda, is at 45%, as Sau collects all its water for the time being. And the Darnius-Boadella reservoir has also skyrocketed in a way it hasn't seen in a long time: it has gone from 17% before the rains to 65% now. Let's remember that at the beginning of March, there were still municipalities in Alt Empordà that were in a state of emergency, something that is now a long way off.

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 57% full, while the Sant Ponç reservoir is already at 78%. Since the historic DANA (Difference in Reservoir Capacity), 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 55%, and the Siurana reservoir, which was empty, is now over 24%. 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. The Rialb reservoir has had to open its floodgates.

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 80%.

One-year evolution of reservoir recovery

This 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. So, all in all, 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 point 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 Council) 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% observed in 2012 with the 21% CAT, which calculates this 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.