Green Water and Blue Water, the Alps and the Climate Change

Thanks mostly to the work of Theodoros Mastrotheodoros and Simone Fatichi (GS), we submitted a paper to Nature Climate Change that was entitled "More green and less blue water in the Alps during warmer summers" which was eventually accepted. It  investigates under the climate change pressure the partition on water between runoff and evapotranspiration on the whole Alps with simulation on a grid of 250 m.

It is not certainly the first effort on the Alps. However,  for its resolution and quantity of data used the paper marks a benchmark for present research. Here it is its abstract:

Climate change can reduce surface-water supply by enhancing evapotranspiration in forested mountains, especially during heatwaves. Here, we investigate this “drought paradox” for the European Alps combining a new database of more than 1200 stations and hyper-resolution ecohydrological simulations to quantify the blue (runoff) and green (evapotranspiration) water fluxes. We show that during the historical 2003 heatwave, evapotranspiration in large areas over the Alps was above average, despite the exceptionally low precipitation, amplifying the runoff deficit by 32% in the most runoff- productive areas (1300 to 3000 m above the sea level). An increase in air temperature by 3 °C could enhance annual evapotranspiration by up to 100 mm (45 mm on average), which would reduce annual runoff at a rate similar to a 3% precipitation decrease. This suggests that green water feedbacks, which are often poorly represented in large-scale model simulations, pose an additional threat to water resources, especially in dry summers. We conclude that integrating hyper-resolution ecohydrological modelling into climate change impact assessment studies can support more realistic predictions of water availability in mountain regions.

By clicking on the figure you can access a preprint.