General-circulation-model simulations of future snowpack in the western United States

April 1 snowpack accumulations measured at 311 snow courses in the western United States (U.S.) are grouped using a correlation-based cluster analysis . A conceptual snow accumulation and melt model and monthly temperature and precipitation for each cluster are used to estimate cluster-average April 1 snowpack. The conceptual snow model is subsequently used to estimate futu re snowpack by using changes in monthly temperature and precipitation simul ated by the Canadian Centre for Climate Modeling and Analysis (CCC) and the Hadley Centre for Climate Prediction and Research (HADLEY) general circula tion models (GCMs). Results for the CCC model indicate that although winter precipitation is estimated to increase in the future, increases in tempera tures will result in large decreases in April 1 snowpack for the entire wes tern US. Results for the HADLEY model also indicate large decreases in Apri l 1 snowpack for most of the western US, but the decreases are not as sever e as those estimated using the CCC simulations. Although snowpack condition s are estimated to decrease for most areas of the western US, both GCMs est imate a general increase in winter precipitation toward the latter half of the next century. Thus, water quantity may be increased in the western US; however, the timing of runoff will be altered because precipitation will mo re frequently occur as rain rather than as snow.