Moisture Budget of Precipitation Extremes in a Warming Climate

Climate ensembles with the Community Earth System Model (CESM) are presented both for the present and a projected future (2071-2080) climate with 40 ensembles in each group, investigating changes to the global moisture budget. Vertically integrated column water vapor (CWV) and moisture flux are analyzed and different terms in the moisture-budget equation separated. This analysis allows an investigation of how changes in precipitation in the future climate are attributable to changes in the moisture content of the atmosphere (the thermodynamic term) versus changes in the circulation (the dynamic term). To compensate for the greater moisture content in the future climate, the present and future climates are compared based on percentile of CWV in the respective climate, so that extremes in the present and future climates may be compared. There is no qualitative difference in results based on the percentile of precipitation, meaning that precipitation is near-monotonic increasing with CWV in the respective climate. In contrast to a comparison of the present and future climatologies, this analysis permits an investigation of how the mechanisms driving global precipitation extremes change in the future climate. Geographical regions are highlighted where changes in climatological precipitation do not match changes in extreme precipitation in the future climate. Precipitation-producing weather systems at specific times of year and locations, e.g., monsoons and extratropical cyclones, are analyzed separately with an eye to understanding how extreme precipitation in a given weather type is modified due to changes in moisture content as well as circulation.