Turning the water cycle upside down in Spain

River in Catalonia

Within 50 years there won’t be any glacier left in the Pyrenees: this showed a study published recently in the scientific journal The Holocene and carried out by a team of researchers from three Spanish universities. Still 21 glaciers are present these days, 10 of them on the Spanish side of the mountain range. However, in 2050 it seems that they will all have been disappeared. Less snow means less snowmelt in spring. In Spain this implies less runoff flowing to the water reservoirs and thus less drinking and irrigation water available in summer.

Water in the form of snow forms a crucial reservoir: a part of the precipitation falling during the winter season is kept in a frozen state before it melts in spring when the dryer seasons start and the water demands are higher. Recently the results were presented of more than 20 years the national monitoring program ERHIN of snow and glaciers in Spain. Data showed that in the Pyrenees about a third of the runoff in the melting season comes from snow resources. This study confirmed a negative trend in annual snow water equivalents during the last 20 years.

Especially in Catalonia water reservoirs are relatively small compared to most other arid regions in Spain. In consequence water has a small lifetime in these reservoirs making water availability more sensitive to droughts. This is only one of the causes that made the Catalan politicians to be on pins and needles during spring this year, planning even to ship water from other regions to the Barcelona harbour. The giant desalination plant on the edge of Barcelona will soon give some relieve, promising to provide 180,000 cubic metres of water a day.

Management of the water reservoirs in the Pyrenees is a multi-objective optimization problem. The reservoirs fulfil three purposes: hydropower generation, flood control and water storage. The three hypothetical objective functions are far from identical: for example flood control has its optimum at a low water level, while for hydropower a full reservoir is most profitable. If water supply becomes even more irregular due to the negative trend in snow accumulation, to find the best set of time-dependent parameterizations of the management system might turn even more difficult than it already was. Let’s hope that a way out is the use of sea water, reducing the optimization problem and allowing a more straightforward solution.

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