Permalink : http://hdl.handle.net/2115/49058

JaLCDOI : 10.14943/gbhu.75.59

In regions covered with a thick layer of snow, snow melting occurs at the snow-ground interface during the winter, a process we call snowpack bottom melting (SBM). To examine the spatial variation of the SBM rate and to estimate its watershed average value, field observations were made in a nival mountainous watershed in northern Hokkaido, Japan. Three different methods were adopted to determine the SBM rate, namely, heat flow calculation, snow lysimeter, and snow pit-wall observation methods, and we found the heat flow calculation method to be the most reliable among the three methods. SBM rates were measured using the heat flow calculation method at 7 sites in the watershed, where each site was selected by considering the slope or flatness, whether it was south- or north-facing, the vegetation, and the elevation. The SBM rate on the south-facing slope was larger than that on north-facing slope, and it was smallest in the forested site. Spatial differences in the SBR rate did not depend on the snowpack condition, but on the ground condition, especially on the gradient of soil temperature near the ground surface. Winter streamflow recession analysis taking into account a steady SBM input showed that 20 % to 30 % of SBM was supplied to the groundwater reservoir and contributed to winter streamflow.