Better Exploration of Drought Risks Under Climate Change Uncertainties using Locally Relevant Climatic Drivers

Drought is expected to intensify under climate change, leading to increasing impacts on society and ecosystems. Well-informed preparedness against these changes is confronted by substantial uncertainty in regional climate responses, as different Global Climate Models (GCMs) produce a wide range of changing signals under the same emission scenario. Multi-model means are commonly used to address this uncertainty which may mask the inter-model variability, and in some cases, the opposing signals across models further reduce the overall change, thereby limiting the risk exploration. Recent work suggests that clustering GCMs based on local impact drivers can improve the representation of plausible future climates and their associated extremes. In this study, we apply the climatic impact-driver (CID) clustering approach to explore future drought risk in the Guadalquivir River Basin, Spain. Both hydrological and agricultural drought were quantified using outputs from the wflow_sbm model and crop water requirements. Seasonal CMIP6 changes in precipitation and potential evapotranspiration (PET) were analyzed using the random forest scoring technique to identify the dominant climatic drivers for drought impact. Our results indicate that winter and autumn precipitation deficits are the main drivers of streamflow drought, while winter increases in PET act as a secondary driver of extreme and multi-year hydrological drought. In contrast, summer and spring increases in PET  emerge as the dominant driver of agricultural drought. Based on these identified drivers, we are going to cluster the GCMs for different future horizons to compare the resulting impact ranges with traditional emission-based ensembles. This ongoing research suggests that drought-specific clustering provides a more informative set of impact scenarios than SSPs. As such it supports robust adaptation planning for water managers under uncertain climate change impacts in Mediterranean river basins.