The average areal water equivalent of the seasonal snow cover on 1 April in the basin of the Rio Grande at Del Norte, Colorado (3419 km³, 2432-4215 m a.s.l.) is evaluated from periodical snow cover mapping by Landsat. A dry, near-average and wet hydrological year are examined. Snow reserves in terms of water storage volumes are computed in three elevation zones for actual temperatures and for a projected climate change of +4°C. The decrease of snow accumulation in a warmer climate results in a significant increase of the winter runoff and a corresponding decrease of the summer runoff. The computed winter/summer proportions change from 24/76% to 29/71% in dry year 1977, from 13/87% to 28/72% in the average year 1976, and from 7.5/92.5% to 12/88% the wet year 1979. An assessment of the seasonal recession from winter to summer reveals that the actual climate effect is even greater.