Proneness of European catchments to multiyear streamflow droughts

Droughts can have severe ecological, social, and economic impacts. Some impacts are particularly severe if droughts last longer than 1 year and water stores are not fully replenished. The proneness of European catchments to multiyear droughts has not been studied extensively, even though such events pose a great challenge for water resources management in many regions. In this study, we assess regions and catchments in Europe that might be prone to multiyear droughts by stochastically simulating long discharge records. The simulation approach uses phase randomization and the flexible, four-parameter kappa distribution to generate potential realizations of (long) drought events. Both observed and stochastically simulated series are used to identify multiyear drought events. Catchments prone to multiyear droughts are located in southern France, central Europe, and southwestern England. To assess potential future changes in the proneness to multiyear events, we follow a purely empirical approach. We link the proneness of a catchment to multiyear events to its low-flow regime as described by the seasonality ratio. Our results show that catchments with a melt-dominated flow regime are generally not affected by multiyear droughts, whereas many catchments with a rainfall-dominated flow regime show such proneness. We further find that catchments experiencing regime changes toward a rainfall-dominated flow regime might be more affected by multiyear droughts in the future. Overall, four regions stood out that might potentially become more affected in the future if historical trends in regimes continue: southeastern England, southeastern France, central Norway, and the Pre-Alps.