Drought propagation in the Rhine River basin and its impact on navigation using LAERTES-EU regional climate model dataset

Abstract. Drought events have become more frequent in Europe over the past decades. The shipping and industrial sectors are severely affected by these events, e.g., due to significant reductions in water levels in the Rhine River and interruptions in the transport of goods. Hydrological droughts in the Rhine closely resemble extreme meteorological droughts identified using the Standardized Precipitation Evapotranspiration Index (SPEI) over both short and long periods. However, the possibility of determining low water level events using non-observed meteorological data, e.g., from large regional climate model datasets, and their implication on navigation has not yet been explored. The main objective of this study is to utilize the Large Ensemble of Regional Climate Model Simulations for Europe (LAERTES-EU) to search for extreme drought years, to assess their contribution to discharge, and to determine possible navigation restrictions on the waterways in the Rhine. We employed a methodology that evaluates the SPEI values to identify meteorological drought, which are then used to obtain discharge values by applying the hydrological model WRF-Hydro. The top 10 most extreme meteorological drought events in the LAERTES-EU dataset are considered in this study, assessing drought propagation by using the SPEI. These events displayed different degrees of severity in terms of duration and reduction of the streamflow as measured by the navigable threshold GlQ20 than the extreme drought observed in 2018. In the selected gauges, several LAERTES-EU events were ranked above 2018 when comparing them with the historical records in terms of mean discharge of the period June–November. These results imply that, even under today's climatic conditions, the streamflow values in the Rhine can be substantially worse than in 2018, generating costly economic and ecological consequences if mitigation measures are not implemented.