The influence of snow depth on the variation of vegetation activity and evapotranspiration

The influence of snow conditions on the seasonal variation of vegetation and evapotranspiration were investigated in a low snow year (1998), a normal snow year (1999) and a heavy snow year (2000). First, a NDVI (Normalized Difference Vegetation Index), evapotranspiration and a snow cover map were composed with NOAA/AVHRR data. The Warm Index (WI) was compiled with meteorological data. Secondly, seasonal variation of NDVI and evapotranspiration were evaluated considering WI and the snow area map. Finally, the spatial distribution of vegetation growth ratio to temperature increase was calculated with the proposed new index. The results indicate that vegetation activity and evapotranspiration in the snowmelt season are related to the area of the remaining snow-covered area because snow cover restrains plants from vegetating. Next, the vegetation growth ratio to temperature increase is greater in the low elevation area, less in the middle elevation area and greater in the high elevation area. This shows the relationship between snow condition and vegetation types.