Assessing climate change impacts on water availability in southern Portugal using a daily sequential soil-water budget model

Abstract

Climate change poses a significant threat to water resources in southern Portugal. To understand the potential impacts on surface and groundwater resources, this study employed a daily sequential soil-water budget model (BALSEQ) under two representative concentration pathway (RCP) scenarios, RCP 4.5 and 8.5, spanning the periods 2020–2060 and 2061–2100. An analysis of meteorological observations and EURO-CORDEX climate projections showed a decline in annual rainfall, particularly under RCP 8.5. Monthly rainfall patterns exhibited significant decreases occurring from March to June, while in December and January, rainfall is likely to increase in all RCP scenarios and respective time-windows. Potential evapotranspiration (PET) demonstrated an increase across all scenarios. BALSEQ model simulations showed a likely decrease in deep infiltration (Ip) and direct runoff (Ed) under both RCP scenarios. The river basins with the highest reductions in Ed and Ip are Mira, Barlavento, southern Guadiana, and Sotavento. For instance, Ed is projected to decrease by up to 87% in Guadiana (RCP 8.5 [2020–2060]). Similarly, Ip is projected to decrease by up to 60% in Sotavento (RCP 8.5 [2061–2100]). These findings highlight the need for adaptation and mitigation measures to preserve the region’s water resources.