The effects of global warming on flood properties in small-medium Mediterranean catchments

Climate change impact on floods and water resources is crucial for planning adaptation strategies. This is especially true in Mediterranean regions where a decrease in precipitation and an increase in extreme rain rates are projected.  Global climate models and common hydrological models are often too coarse to represent rainfall properties and hydrological processes in these regions due to their scale. Therefore, the current understanding of climate change's impact on hydrological properties and processes in Mediterranean catchments is missing. To resolve this, we utilize the high-resolution (1 km2) weather research and forecasting (WRF) model (abstract #EGU22-1996). Rainfall simulations were input to a distributed hydrological model (<60 s, 100 m2 GB-HYDRA). Explicitly, we apply spatially-shifted ensemble results for 41 couples of heavy precipitation events in historic (end of 20th century) and future (end of 21st century; RCP 8.5 scenario) climate conditions to 4 small-medium-size basins (18–69 km2) in the eastern Mediterranean. Ensemble average total precipitation decreased by 24% between historic and future events. This resulted in an average decrease in outlet peak discharge (-20%, non-significant), and a significant drop in the total flood volume (-27%) in future events. This change can be attributed to a significant (-25%) decrease in runoff contributing area (RCA); hillslope sections from which water flows, reaches the stream network, and consequently, the basin outlet and significant decrease of the averaged rainfall rates over them (-22%). The results of this study suggest that ongoing climate change in Mediterranean regions is expected to have a considerable impact on the flow regime, and thus, practical actions should be taken.