Rethinking future flood hazard: Hourly data challenge daily flood projections in Alpine catchments

This study challenges a common misconception in current flood hazard research that floods will decrease under a warming climate in many rivers due to changes in land-surface processes, particularly decreases in snowmelt. This view persists because most studies on flood changes rely on daily resolution data, which masks flood changes due to subdaily rainfall intensification. We show that daily streamflow projections systematically underestimate flood changes compared with hourly projections in Alpine catchments. Our results highlight that the sign of change can even switch from negative to positive in strongly snow-influenced catchments when taking an hourly perspective because intensified subdaily precipitation can outweigh snowmelt decline. These results highlight that using daily instead of hourly projections may lead to wrong conclusions on both the magnitude and direction of flood changes. An hourly resolution perspective is, therefore, crucial to reliably guide adaptation strategies to extreme Alpine floods in a warming world.