Accelerated propagation from meteorological to hydrological drought under diminishing snow

Abstract

Understanding the spatial-temporal evolution of drought propagation is crucial for improving our monitoring and prediction of droughts. However, the impact of changing snow dynamics on drought propagation time (t_P) has rarely been assessed. Utilizing observed streamflow and reanalyzed climate data from ∼900 northern snow-affected catchments, here we provide a comprehensive investigation on temporal changes in t_P and underlying mechanisms in the context of diminishing snow. Results show that catchments with a higher fraction of precipitation falling as snow (f_s) exhibit a longer t_P compared to catchments with marginal snowfall. Over the past 70 years, t_P has significantly decreased following decreased f_s, indicating accelerated drought propagation in a snow-diminishing world. Specifically, for catchments with lower mean annual f_s ($\overline{f_{\text{s}}}$⩽ 30%), t_P is decreasing at a rate of −0.8 d per decade. In contrast, for catchments with higher $\overline{f_{\text{s}}}$ ($\overline{f_{\text{s}}}$> 50%), t_P is decreasing at a rate of −3.4 d per decade, four times faster than the rate observed in low-$\overline{f_{\text{s}}}$ catchments. This acceleration is attributed to a reduced total snowmelt and slower snowmelt rate during the drought propagation process, which decreases streamflow recharge from snowmelt and increases evaporation losses. These findings are important for enhancing drought prediction and risk management in snow-affected regions.