WATER AVAILABILITY IN SOUTHERN PORTUGAL FOR DIFFERENT CLIMATE CHANGE SCENARIOS SUBJECTED TO BIAS CORRECTION

Abstract

Regional climate models provided precipitation and temperature time series for control (1961–1990) and scenario (2071–2100) periods. At southern Portu gal, the climate models in the control period systematically present higher temp eratures and lower precipitation than the observations. Therefore, the direct inpu t of climate model data into hydrological models might result in more severe scenarios for future water availability. Three bias correction methods (Delta Change, Dire ct Forcing and Hybrid) are analysed and their performances in water availability impac t studies are assessed. The Delta Change method assumes that the observed series variab ility is maintained in the scenario period and is corrected by the evolution predicted by the climate models. The Direct Forcing method maintains the scenario series variabi lity, which is corrected by the bias found in the control period, and the Hybrid method maintains the control model series variability, which is corrected by the bias found in the control period and by the evolution predicted by the climate models. To assess the climate impacts in the water resources expected for the scenario period, a physically based spatially distributed hydrological model, SHETRAN, is used for runoff pro jections in a southern Portugal basin. The annual and seasonal runoff shows a runoff d ecrease in the scenario period, increasing the water shor tage that is already experienc ed. The overall annual reduction varies between –80% and –35%. In general, the results show that the runoff reductions obtained with climate models corrected with the Delt a Change method are highest but with a narrow range that varies between –80% and –5 2%.