Asymmetry in snow-water nexus in mountain areas mainly governed by meteorological seasonal changes.

Despite the importance of snow cover and related streamflow changes in mountain catchments worldwide, hitherto the quantification of their mutual variability has not been addressed at this scale. This work utilizes satellite and ground observations spanning the last two decades to investigate the nexus between snow cover and streamflow across 548 mountain catchments globally. The results show that around 5% of these catchments are simultaneously affected by significant trends in both variables. This happened mainly in the Andes Cordillera, where snow season ends 28 days earlier, with a snow cover area reduction of about 15%, and a decrease in annual streamflow of 67 m3/s. Moreover, in 16% of the catchments, significant changes occur only in one of the variables. This asymmetric behaviour was connected with significant changes in a specific season. When the most affected season is summer, with marked temperature increase, snow changes are not reflected in streamflow, as the latter mainly depends on spring snowmelt, as observed in the European Alps. When there is an increase in winter solid precipitation, this may not be reflected in yearly snow cover changes but can impact the resulting streamflow, as shown in the western North American catchments.