Changes in Snow Drought and the Impacts on Streamflow Across Northern Catchments

Snow drought, characterized by an anomalous reduction in snowpack, exerts profound hydrological and socioeconomic impacts in cold regions. Despite its significance, the influence of diverse snow drought types, including warm, dry, and warm-and-dry variants, on streamflow remains inadequately understood. Here we present the first hemispheric-scale, observation-based assessment of snow drought patterns and the impacts on seasonal and annual streamflow (Q) across 3049 northern catchments over 1950–2020. Our findings reveal that catchments with a lower mean annual snowfall fraction ($\overline{f_{\mathrm{s}}}$) exhibit a heightened prevalence and severity of warm and warm-and-dry snow droughts, whereas high-$\overline{f_{\mathrm{s}}}$ experience a more prevalent but less severe dry snow drought. This disparity arises from distinct sensitivities of snowpack to cold-season precipitation and temperature. In addition, dry and warm-and-dry snow droughts induce a reduction in Q during both cold and warm seasons, culminating in a significant decrease in annual Q. Conversely, warm snow drought increases annual Q in catchments with $\overline{f_{\mathrm{s}}}\le 0.3$ but decreases annual Q in catchments with , attributable to a trade-off between increased cold-season streamflow (Q_c) and decreased warm-season streamflow (Q_w). With ongoing climate warming, a continued reduction in snowfall is anticipated, which is expected to further increase the frequency and severity of warm and warm-dry snow droughts. These circumstances, particularly impactful under low $\overline{f_{\mathrm{s}}}$ conditions, are poised to present formidable challenges for water resources management in cold regions globally.