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The effect of a hypothetical temperature increase of +4degreesC on snow cover and on year-round runoff is evaluated for the very humid basin Illecillewaet (1155 km(2), 509-3150 m a.s.l., British Columbia, Canada), the semi-humid basin of Kings River (3999 km(2), 171-4341 m a.s.l., California, USA), and the semi-arid basin of Rio Grande at Del Norte (3419 km(2), 2432-4215 m a.s.l., Colorado, USA). In contrast to current methods of evaluating the climate effect, a realistic seasonal snow cover from satellite monitoring is used to represent the present climate. The non-calibrated SRM model is applied to transform this snow cover under conditions of a warmer climate and to compute the climate-affected runoff.

The winter snow accumulation is particularly reduced in the Kings River basin which has the greatest elevation range. In absolute terms, the smallest snowpack reduction occurred in the semi-arid basin of Rio Grande at Del Norte. The decline of snow covered area in the snowmelt season in accelerated by about one month in all basins. The runoff in the winter half year is about doubled at the expense of the summer half year in the basins Illecillewaet and Kings River. This effect is smaller in the basin Rio Grande at Del Norte. Because the climate change was limited to a temperature increase, there is no significant change in the yearly runoff volume in the basins Kings River and Rio Grande. There is a yearly runoff increase in the Illecillewaet basin due to enhanced glacier melt.