Anticipated Changes in Precipitation Events over the 21st Century Using Community Climate System Model, version 4

Future global daily precipitation data from Community Climate System Model, version 4 (CCSM4) were analyzed to evaluate changes in a variety of precipitation parameters over the 21st century. Multiple ensemble members of 21st century Representative Community Pathways (RCP) radiative scenarios were included in the model to provide an array of potential future climate change results. Multiple ensembles of historic daily precipitation data from CCSM4 were compared with Global Precipitation Climatology Project (GPCP) V1DD daily precipitation data and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) monthly precipitation data. Annual average and 95th percentile precipitation values were averaged from 1997-2005 among the datasets, and correlation coefficients (R) are relatively high (0.8796 and 0.8530 for average precipitation and 0.8820 for 95th percentile values) between CCSM4 and observational data. Analysis of mid and end-of-21st century changes in average and 95th precipitation values, reveals large increases in most locations and slight decreases across a few regions. Nearly identical spatial patterns exist between the parameters, though the magnitude of change varies. Magnitudes of change in 95th percentile values exceed those of average precipitation, but the relative change is spatially similar. Extreme indices R95T and DA95 indicate widespread increases in the annual contribution of total precipitation from extreme events with a simultaneous increase in frequency of such events, while some locations show decreases. Regional analysis of the four precipitation parameters results in similar findings but provides additional temporal information. Increasing changes in all parameters occur under with increases in radiative forcing. Division of daily precipitation into categories based on intensities reveals sharp increases in annual precipitation contribution from the most intense precipitation events and a subsequent decreasing contribution from less intense events. Under the highest radiative forcing scenario (RCP 8.5), temporal comparison between the annual contribution from the six precipitation categories and atmospheric carbon dioxide concentration yields R values of -0.979, -0.977, -0.753, 0.830, 0.971, and 0.969, respectively. These results indicate a direct relationship between anthropogenic greenhouse gas emissions and global precipitation trends, stressing the need to adapt to and mitigate impacts of climate change.