Mountain snow cover typically develops in the autumn and grows to a maximum depth in early spring. As day length and sun angles increase, so do air temperatures, causing snow cover to warm and begin to melt. Snow cover balances the availability of water in mountain environments. Where winter precipitation falls as rain, surface runoff occurs almost immediately. In contrast, snow stores water during the winter and then melts in the spring and early summer, creating peak stream flows in the afternoon and an overall seasonal peak flow. In many semi-arid mountain environments, snow melt buffers the transition into the dry summer season. Mountain snow is also a key source of groundwater, since a significant portion of the snow melt enters the soil and drains downhill into valley sediments. The timing, spatial distribution, and volume of snow melt are critical for determining how much water flows as surface runoff into rivers and lakes and how much becomes groundwater. This figure presents the annual snowfall distribution for a typical mountain environment, exemplified by Columbine Pass in Colorado, USA. Snow water equivalent is a typical measure of snowfall and snowpack, where snow is measured as the amount of water it represents, when melted.
From collection: Global Outlook for Ice and Snow
Hugo Ahlenius, UNEP/GRID-Arendal