A comparison of annual streamflow sensitivities to vegetation change and climate variability in fourteen large watersheds along climate zones in China

Extensive studies have revealed the impacts of climate variability and vegetation change on annual streamflow. However, the response intensity of annual streamflow varies among watersheds owing to differences in climate and watershed properties, which have rarely been assessed, especially for streamflow sensitivity to forest change. This calls for studies to evaluate annual streamflow sensitivity, defined as the annual streamflow response intensity (%) per unit of external change (%), to better interpret variations in annual streamflow responses among watersheds as well as their associated driving mechanisms. In this study, we estimated and compared annual streamflow sensitivities to vegetation change (Sv) and climate variability (Sc) by applying a five-step framework in 14 large watersheds in China and disentangled the contributions of their associated key drivers. We found that Sv was significantly greater than Sc, suggesting that annual streamflow was more sensitive to vegetation change than to climate variability in 11 watersheds. Alpine watersheds have the lowest Sv because of water plays a minor supportive role in vegetation growth under low effective precipitation and leaf area index, whereas higher topsoil salinity, which largely promotes water movement, contributes to a high Sv in temperate watersheds. Temperate watersheds also have a large Sc because their climate is dry and the resilience of their topography to climate variability is low. The relative contributions of the associated key drivers showed that Sv was determined by topography (36.35%), soil (33.68%), landscape patterns (12.22%), vegetation background (9.26%), and climatic conditions (8.49%). In contrast, Sc was mostly controlled by topography (54.39%) and climatic conditions (33.08%), followed by vegetation background (12.53%). This study highlights that the management paradigm for maintaining sustainable water resources should focus on both climate and vegetation changes considering the differences in watershed properties in a changing environment.