Water Flow through Snow and Firn

Abstract Water flux through snow and firn has important implications for the timing and magnitude of runoff from seasonal snowpacks, glaciers, and ice caps. Studies conducted over the last few decades have greatly improved our understanding of water flux through snow and firn, including knowledge of the development of wetting fronts as meltwater enters dry snow, preferential flow paths, grain growth of wet snow, and the growth of ice layers and ice columns within the snowpack. Such studies have resulted in the development of a variety of analytical and numerical models for calculating runoff from melting snow and firn. Although our understanding of key processes continues to increase, there are major gaps in our knowledge that limit our ability to formulate comprehensive physically based models of snow metamorphism and water flux through snow and firn. Part of the problem is a lack of data, which is due to the great difficulty of conducting experiments on snow near 0°C and our inability to measure the properties of snow required for estimating the value of parameters needed for numerical simulations. In order to overcome these problems, there is a need for the development of new measurement techniques and carefully designed field and laboratory experiments. Comprehensive models are required for predicting not only melt runoff, but also the release of pollutants from the snowcover, the large‐scale properties of the snowcover necessary for understanding large‐scale energy‐balance and global‐change problems, and the release of meltwater from cold glaciers and icecaps under future climate scenarios.