Drought decreases streamflow response to precipitation especially in arid regions

Abstract. Persistent drought conditions may alter catchment response to precipitation, both during and after the drought period, hindering accurate streamflow forecasting of high flows and floods. Yet, the influence of drought characteristics on the catchment response to precipitation remains unclear. In this study, we use a comprehensive dataset of global observations of streamflow and remotely sensed precipitation, soil moisture, total water storage and normalized difference vegetation index (NDVI). Using multivariate statistics on 4487 catchments with a stationary streamflow-to-precipitation ratio, we investigate the influence of drought on fluctuations of streamflow sensitivity to precipitation. Our analysis shows that generally droughts with streamflow or soil moisture anomalies below the 15th percentile lead to around 20 % decrease in streamflow sensitivity to precipitation during drought compared to the historical norm, with up to a 2 % decrease one year after the drought. Negative NDVI anomalies are the only exception, resulting in a 3 % increase in sensitivity. These effects are more pronounced when droughts are longer and more severe. Most changes were found in arid and warm-temperate regions, whereas snow-influenced regions exhibit less sensitivity changes due to drought. In addition, we used step-change analyses on 1107 catchments with non-stationary streamflow-to-precipitation ratio to identify significant abrupt shifts on the timeseries, examining the role of drought in driving these shifts. This analysis revealed both positive and negative shifts in streamflow sensitivity after severe and persistent drought conditions regardless of climate and catchment characteristics. Positive shifts occur only when the drought propagated through the hydrological system after extended dry periods, while negative shifts are usually linked to shorter, intense dry periods. This study sheds light on the importance of considering climate characteristics in predicting dynamic catchment response to precipitation during and after persistent drought conditions.