Effect of melting at the snow-ground interface on the runoff during winter.

Abstract

The specific runoff in a snowy region is, in general, larger than that in a snow-free region. In a region with deep snow, the bottom layer of the snowcover melts by the conductive heat from the ground during the winter. We investigated the quantitative influence of the bottom-melt to the stream flow. We measured the bottom-melt and the river runoff in an experimental watershed under deep snow and severe coldness conditions during two winter seasons. The bottom-melt was measured by two different methods at our field station in the watershed. In one method the meltwater was measured directly by a lysimeter. And in the other, the heat flux in the ground and in the snowcover were measured to estimate the melting heat energy. The amount of bottom-melt was estimated by numerically calculating the heat flux in the snowcover from the air temperature and snow depth. Simulation of runoff amount was achieved successfully by using the tank model. We also calculated the runoff water in the case of no bottom melt. This calculated runoff amount was half of the observed one in March. The bottom-melt supplied about a half of the runoff water to the watershed. These results indicate that the bottom-melt of snow plays an important role in the water balance during the winter.