Estimation of regional snow-line elevations in Norway. Testing a method for estimating RSLE and melt slope analysis in Norway.

Abstract

Snow plays an important part in the hydrology of high latitude and mountainous areas. In Norway about 30% of the annual precipitation falls as snow. Therefore it is important to properly quantify the seasonal snow cover in Norway. In this study a method to calculate regional snow-line elevations (RSLE) was evaluated in 70 catchments in Norway to see if the method is a viable option in the difficult conditions faced in Norway and if so can the results be used to study melt behavior in those same catchments. MODIS snow cover maps were used as input data when estimating the RSLE. An alternative approach used seNorge to calculate RSLE. The results from the seNorge RSLE calculations were used both to assess the reliability of the MODIS RSLE as well as for subsequent analysis regarding the climatology of the catchments. The two datasets were compared to see the effects of cloud cover has on them and if the RSLE would could provide a simple viable alternative to snow cover area (SCA) estimations as well as if the RSLE dataset could be used to identify melt periods and the factors driving variability in them. The method was implemented in all the catchments over the period from 2000 – 2016. Results show that when the SCA estimated using MODIS and seNorge data is compared, cloud cover within the catchments has significant effect on the fit between the two datasets while the clouds have hardly any effect on the RSLE estimated from the same datasets. Based on the seNorge RSLE melt slopes were estimated using the duration of melt period and elevation change in RSLE during melt period. Analysis of factors effecting variability in melt slopes suggest that, the elevation range, mean elevation and peak SWE are the factor that most affect melt slope variability. The effect of rain on snow events on melt slopes indicated that they had no significant effect on melt slopes as they are estimated in this study. The melt slopes estimated using RSLE data seem to give some indications of what drives melt rates but is not a very robust indicator. The RSLE method is promising and seems to work well in the conditions faced in Norway but needs further validation using observations.