Spatial Distribution of Precipitation Seasonality in the United States

A detailed, long term portrait of the seasonality of precipitation over the United States is developed using a 90 year climate division record. Selected decadal maps of seasonality are also presented, and their variability over time considered. Relationships between significant changes in precipitation or temperature and seasonality were sought, but not found. Model output from four global climate models (GCMs) are analyzed with respect to precipitation seasonality over the same area, both for present conditions, and for a doubled CO2 climate. Comparison of model output to present patterns suggests that in most cases the models are doing reasonably well in matching regional details of seasonality. For the future climate, there is some agreement among models suggesting a trend toward a spring, rather than summer precipitation maximum in the midcontinental areas of the United States.