Though limited in extent, seasonal snowpacks in the Earth's mountain ranges account for the major source of the runoff for stream flow and groundwater recharge over wide areas of the mid-latitudes. In most alpine regions, snowmelt runoff is responsible for the annual maximum instantaneous discharge and most of the annual flow. It is therefore important to understand the processes controlling snowmelt runoff and its chemical composition for both water resources as well as ecological reasons.
Progress in snow hydrology over the past quadrennium has been heavily influenced by the availability and anticipated future availability of remote sensing data at times and spatial scales appropriate for addressing local, regional and global hydrologic issues [ Dozier, 1992]. Recent research has examined topics contributing to better estimation of snowpack properties, snow distribution, snowmelt, and related chemical and biological questions. This review focuses mainly on seasonally snow-covered alpine areas, but includes other research potentially applicable to alpine areas of the Earth.
Understanding the linkages between the processes controlling snow accumulation and melt is critical to developing a predictive ability to describe the response of a basin to changes in inputs of water, energy and chemicals. Due to their steep, variable topography, alpine catchments are characterized by a large degree of heterogeneity in the important properties controlling snow accumulation, snowmelt and meltwater runoff. In a recent National Research Council report [ National Research Council, 1991], it was emphasized that ``... one of the main obstacles in understanding surficial processes is the high spatial variability of surface features and hydrologic variables.'' The hydrology of snow-covered areas was one of the ``critical and emerging'' areas identified in the report for future research. The report also emphasized that chemical and biogeochemical processes in the watershed must be integrated with our knowledge of the snow hydrology.