Sensitivities of mean and extreme streamflow to precipitation variability across Europe

Understanding large-scale patterns in streamflow response to precipitation variability helps identifying places where precipitation changes most strongly affect streamflow. This study presents the sensitivity of annual streamflow of over 8,000 European catchments to annual and seasonal precipitation variability, as measured by observation-based streamflow elasticities. We extend the scope of the conventionally studied mean flows by incorporating annual maximum and minimum flows as well. As anticipated, both annual mean and extreme flows generally increased with higher annual mean precipitation. On average for Europe, a 1% change in annual precipitation on average resulted in an amplified flow response of 1.2% in annual mean flows, an even stronger amplification of 1.3% in annual maximum flows, and a dampened response of 0.9% in annual minimum flows. These elasticities exhibited distinct regional patterns. Northern Poland and the Baltic States featured remarkably insensitive mean and extreme streamflow. Furthermore, annual maximum flows in the mountainous Central Europe were highly sensitive to summer precipitation. In Spain, a high elasticity of mean and maximum flows to winter precipitation was observed. The elasticity of low flows appeared to be more localised and less related to precipitation variability. We then employed a random forest model that incorporated 20 climate and catchment characteristics to examine their relationship with streamflow elasticities and identify the climate characteristics exhibiting the strongest correlation. Despite the high number of characteristics included the model’s capacity to predict the elasticities based on the selected input variables was relatively low, suggesting that some key drivers remain unaccounted for. An important factor influencing streamflow elasticities that was not comprehensively addressed through the random forest input variables is human activity. To further explore the human influence on streamflow response to precipitation, we studied approximately 150 Dutch catchments with varying degrees of human influence. We used six hydrological signatures to group the catchments into typologies of similar behaviour and analysed whether these typologies are related to the degree of management. This research advances our understanding of mean and extreme streamflow responses across regional and large scales.