Nearly 150 hm³ of snow, equivalent to twice the capacity of the Oliana reservoir, has evaporated in the Lleida Pyrenees in just three weeks, according to reports from the Ebro Hydrographic Confederation (CHE). High temperatures are causing the snow to sublimate, turning directly into water vapour before it can melt and flow into rivers.

Between 6 and 27 April, snow reserves in the headwaters of Lleida's four major rivers, the Garonne, Segre, Noguera Pallaresa, and Noguera Ribagorçana, decreased from 772.2 hm³ to 246.7 hm³, a reduction of 525.5 hm³. However, only 376.2 hm³ of this snow melted and reached the rivers, meaning 149.3 hm³ evaporated directly into the atmosphere.

This phenomenon, known as sublimation, is the direct transition of a substance from solid to gas. Solar radiation, which has been high since the end of the rains in mid-March, plays a key role in this process. The largest losses occurred in the Segre headwaters, where over 50 hm³ of snow disappeared without melting into the river system. The Noguera Pallaresa and Garonne followed with over 30 hm³ each, while the Ribagorçana lost just over 20 hm³.

Changing Snowfall Patterns

The 149.3 hm³ of evaporated snow is almost double the 85 hm³ capacity of the Oliana reservoir on the Segre river. It is also close to the capacities of Camarasa (162 hm³) on the Noguera Pallaresa and Escales (152 hm³) on the Noguera Ribagorçana. Despite these losses, current water reserves in the reservoirs are high, exceeding 85% in the Segre and Pallaresa systems and 75% in the Noguera Ribagorçana system. Officials say this ensures sufficient water for irrigation and urban supply this summer.

This year's snow season has shown an acceleration of meteorological patterns. The maximum snow volume, over 2,000 hm³ equivalent of water, was recorded in February, making it the highest figure this century. However, snow accumulation started two months later than usual, peaked a month earlier, and reached its minimum two months ahead of schedule. This indicates that more snow is arriving later and disappearing earlier than in previous years, affecting water resource management.

Future Water Scarcity Predicted

Snow reserves in April and May are among the lowest this century, excluding the drought periods of 2022-2024, 2005-2007, and 2011-2012. They are even below some of those drought years. The CHE has worsened its forecasts for river flow reductions in the Ebro basin based on meteorological specialists' conclusions.

A recent study by Cedex predicts a 12.5% increase in the decrease of river system contributions to the basin by 2050. This will be accompanied by rising temperatures and reduced rainfall, leading to increased water needs for crops. Previously, this forecast was only 5%. Similarly, early work on the new Ebro Hydrological Plan (PHE) initially estimated a 7% increase in crop water needs by 2050, but recent studies now put this figure between 13% (University of Castilla-La Mancha) and 16% (Pigall consultancy).

The CHE's updated predictions highlight the growing challenge of water management in the region as climate change intensifies its effects on snowmelt and precipitation patterns. Future decisions will need to address these changing conditions to ensure long-term water security for Catalonia's agricultural and urban areas.