Uncertainty assessment of climate impact indicators in future scenarios projections for water allocation in small catchments

Climate services provide data dealing with future climate scenarios and projections. Climatic models ensemble mean is commonly used as the recommended value to assess climate change effects in impact studies. This ensemble is composed of different combinations of Global Circulation Models (GCM) and Regional Climate Models (RCM), not being a fixed number the quantity of RCM-GCM combinations needed to calculate this ensemble.  Recommendations found in literature indicate a range usually between 5 to 10 endmembers, but the suitability of some of the models is not always included in the assessment of the applications. How to choose correctly these number of models or to reduce its number is an issue currently under debate. In heterogeneous and/or small areas where the spatial significant scales cannot be adequately captured by coarse grids, climatic models often have problem to correctly represent hydrometeorological variables due to the GCM-RCM parameterizations. Moreover, some of these combinations give completely uneven simulated climate regime during the reference period and, consequently, hydrological variables like river flow are poorly simulated from these generated drivers.

This work proposes an alternative methodology to project hydrological variables without using model ensemble mean, selecting only the model that best represent climate regime, defining transfer functions to overpass the spatial scale issues, and assessing uncertainty by using stochastics techniques. The methodology is applied in the Guadalfeo River Basin, a mountainous semiarid watershed in Sierra Nevada (southern Spain), where alpine and Mediterranean climate coexist, and the highest summits of the Iberian Peninsula are located; hence,  snow plays a key role in the water availability and management, and future impacts are key to assess adaptation plans . The projected variables are used to assess changes in climatic impact indicators in future scenarios projections for water allocation for three different end-user sectors: small hydropower generation, water allocation in a reservoir system, coastal municipality dealing with water allocation conditioned by agriculture and tourism. 

 

This work was funded by the project AQUACLEW, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Commission [Grant 690462].