Observed decadal mean seasonal precipitation change

Observed decadal mean precipitation change (deviations from the 1901-1960 average, %) for the Southwest U.S. for winter (top left, blue line), spring (top right, green line), summer (bottom left red line), and fall (bottom right, orange line). Based on a new gridded version of COOP data from the National Climatic Data Center, the CDDv2 data set (R. Vose, personal communication, July 27, 2012). Gray lines indicate 20th and 21st century simulations from 15 CMIP3 models, for the high (A2) emissions scenario. Observed seasonal precipitation variations generally show greater variability than the model simulations for all seasons except summer.