Future changes in the distribution of daily precipitation totals across North America

[1] Shape and scale parameters of the two-parameter gamma distribution were estimated for daily distributions of precipitation at individual grid-points in two General Circulation Models (HadCM2 and CSM). Maps of changing parameter distributions under anthropogenic forcing show the extent to which future precipitation scenarios for North America are consistent with observed trends in the 20th century. The scale parameter is found to be more variable, both spatially and temporally, than the shape parameter. Patterns of changes in mean wet-day amounts are strongly correlated with changes in the scale parameter. While the two models show quite different results for the spatial patterns of change, both indicate that the proportion of total precipitation derived from extreme and heavy events will continue to increase relative to moderate and light precipitation events.