The estimation of snowmelt runoff using the model considered the characteristics of snow distribution outside of forests.

Terumasa Nishihara, Makoto Nakatsugawa, Tomohide Usutani

Thursday 2 july 2015

11:15 - 11:30h at Central America (level 0)

Themes: (T) Water resources and hydro informatics (WRHI), (ST) Catchment hydrology

Parallel session: 11H. Water resources - Catchment

In snowy cold regions, the snow-melt water stored in dams in early spring meets the water demand for the summer season. However, snow-melt water can cause a snowmelt floods. For this reason, many snowmelt runoff models have been proposed for estimating the volume of runoff into dams. Given that snow distributions differ between inside of forests versus outside of forests, we developed a snowmelt runoff model that is able to correct the snow distribution by using observation data from snow surveys. This paper reports the results obtained when the model was applied to some dams in Hokkaido, which is the northernmost island of Japan. The Model consists of three sub-models, first, a snowmelt model and a snow permeation model are applied to meshes of about 1 km2; then, water supply to the ground is estimated for each mesh. After that, water supply to the ground for each mesh in the entire basin are lumped together, and the lumped value is applied to the runoff model to obtain dam inflow. With regard to the correction of snow water equivalent distribution, a correction method that considers topography is applied to meshes inside of forests, a correction method using overground openness as a parameter is applied to meshes outside of forests, and the coefficients for the correction formula are determined based on the results of the annual snow survey. Calculation was performed using the data of the five or the ten snow-melting seasons from 2002 to 2012. The accuracy is higher when this method is employed than when no correction is made; thus, the correction of snow distribution was found to be effective. Since there is no significant difference between when no correction was made and when this method was employed in the early snow-melt season, it is considered that the correction of snow distribution is very effective at high elevations, where snow-melting peaks in the late snow-melting season. At high altitudes above the forest limit, fallen snow tends to be redistributed by strong wind. The snow distribution corrected by means of overground openness gives consideration to the characteristics of snow distribution after redeposition, i.e., after the wind has redistributed the snow. From this, it is assumed that the snow distribution in the high-altitude range was properly corrected, thus contributing to improved accuracy of dam inflow calculation.