The redistribution of runoff in response to global warming may vary in hydrological years of different character as reported by Rango and Martinec (1998). In the present paper, effects of global warming on snow accumulation, snowmelt and runoff are studied in three North American mountain basins with widely varying climate conditions. Although snowmelt is a result of a complex energy balance in mountain basins, the degree-day approach is used as an effective index of this snowmelt so that the Snowmelt RunoffModel (SRM) can be used to assess the effects of global warming. In order to get a clear picture of the effect of increased temperatures, the total precipitation is left unchanged except for conversion from snow to rain when the warmer temperatures dictate.