acquired March 21, 2021
acquired April 12, 2023

Shrinking Reservoirs in Catalonia



The Catalonia region of Spain is experiencing a long-term drought, which has shrunk reservoirs and led to water restrictions. Evidence of the drought stands out in satellite images of two large reservoirs in the region.

The Sau Reservoir (Pantà de Sau) and the Susqueda Reservoir (Pantà de Susqueda) are about 108 kilometers (67 miles) inland from Barcelona and supply the metropolitan area with drinking water. The low water levels of the reservoirs can be seen in the image above (right), acquired by the Operational Land Imager (OLI) on Landsat 8 on April 12, 2023. The image on the left was acquired by the OLI on Landsat 8 in March 2021, when water levels in the reservoirs were higher.

Dams built along the Ter River created these reservoirs in the 1960s and they have become a vital source of water for Catalonia’s residents and farmers.

“Seasonal droughts are typical of Catalonia’s Mediterranean climate—including in the Ter watershed, which runs from the Catalan Pyrenees to the Mediterranean Sea,” said Albert Ruhi, an ecologist at the University of California, Berkeley. “But over the past few months, the lack of precipitation and snowpack has led to the driest spring since 1990 for the Ter River.” Ruhi, originally from Girona, just east of the reservoirs, studies freshwater ecology and how the Ter River is changing over time.

According to the Catalan Water Agency, the Sau Reservoir (left) stood at only 7 percent of its capacity on April 25, 2023. The Susqueda Reservoir (right) also had diminished water levels. That reservoir stood at 38 percent of total capacity on April 25. Across all of Catalonia, reservoirs averaged about one-quarter of capacity.

Notice the tan fringes of exposed rock around the water in the reservoirs. These are areas that were underwater when the water level was closer to capacity, a phenomenon referred to as a “bathtub ring.” Falling water levels in the Sau Reservoir have exposed more than just rock. The belfry of an 11th-century church and a nearby village, which have been mostly submerged since the construction of the dam, became visible in recent months. The belfry is occasionally exposed during times of low water; this year, the church stands several meters above the water line. Note that these features are too small to be seen in these images.

Although much of Spain is experiencing a drought this spring, Catalonia in the northeast has been hit especially hard. Over March and April, the region has received only about 14 percent of expected rainfall based on 2009-2021 averages.

“The lack of spring rain and snowmelt means that this year’s dry season will be twice or even three times as long,” Ruhi said. “This could lead to ecological impacts such as fish mortality and algal blooms.”

In some places in Catalonia, officials have turned to restricting water use among residents and farmers. In the small town of L’Espluga de Francoli, 97 kilometers west of Barcelona, household water supplies are turned off every night between 10 p.m. and 7 a.m. local time. Personal water use has been limited to 230 liters (61 gallons) per person per day in Catalan municipalities representing almost 6 million people.

The lack of rain has been accompanied by high temperatures, with 2022 ranking as Catalonia’s warmest year on record. Between April 26 and April 28, 2023, forecasters are expecting temperatures in Spain to reach 40°C (104°F). Spain’s meteorological agency warned that this could leave large parts of the country susceptible to wildfires.

NASA Earth Observatory images by Allison Nussbaum, using Landsat data from the U.S. Geological Survey. Story by Emily Cassidy.