Earlier streamflow in a snow-dwindling world

Impacts of climate change on water resources tend to be significant in regions where streamflow is substantially sourced as snowmelt from snowpacks1,2. In these areas, as the climate warms and the fraction of precipitation falling as snow (snow fraction, f_s) shrinks, streamflow is generally shifting toward earlier in the year by way of earlier snowmelt and increased proportional rainfall1,3,4. In a recent Article, Han et al.5 call for revision of the ‘less snow equals earlier streamflow’ paradigm, because their analysis indicates that while such paradigm upholds for average annual high-snow-fraction catchments ( f_s>0.5), lower-snow-fraction catchments (0.1< f_s <0.4) experience later seasonal streamflow as snow fractions reduce. Here we use results generated by Han et al.5 to show that trends towards earlier streamflow are instead dominant across the entire defined range of low to high snow-fraction catchments (0.1< f_s<1), supporting the longstanding paradigm. In addition, we use catchment climatological data to demonstrate that comparing streamflow timing between low- and high-snow-fraction years, as used by Han et al.5, is a misleading analogy to study effects of climate-warming-induced snow changes and subsequent streamflow seasonality.