A distributed temperature-index ice- and snowmelt model including potential direct solar radiation

Hourly melt and discharge of Storglaciaren, a small glacier in Sweden, were computed for two melt seasons, applying temperature-index methods to a 30 m resolution grid for the melt component. The classical degree-day method y ielded a good simulation of the seasonal pattern of discharge, but the pron ounced melt-induced daily discharge cycles were not captured. Modelled degr ee-day factors calculated for every hour and each gridcell from melt obtain ed from a distributed energy-balance model varied substantially, bath diurn ally and spatially. A new distributed temperature-index model is suggested, attempting to capture both the pronounced diurnal melt cycles and the spat ial variations in melt due to the effects of surrounding topography. This i s accomplished by including a radiation index in terms of potential clear-s ky direct solar radiation, and thus, without the need for other data beside s air temperature. This approach improved considerably the simulation of di urnal discharge fluctuations and yielded a more realistic spatial distribut ion of melt rates. The incorporation of measured global radiation to accoun t for the reduction in direct solar radiation due to cloudiness did not lea d to additional improvement in model performance.