Summer rainfall variability over the southeastern united states and its intensification in the 21st century as assessed by cmip5 models

The variability of Southeastern (SE) United States (U.S.) summer precipitation in the current and future climate is analyzed using Coupled Model Intercomparison Project-Phase 5 (CMIP5) models. By comparing simulated historical precipitation variability with observations, we categorize CMIP5 models into two groups: Group 1 (G1) models that simulate the summer precipitation variability reasonably well and Group 2 (G2) models that need further improvements. Our analysis suggests that the relatively higher skill of G1 models is attributable to their ability to accurately represent the dynamical linkage between SE U.S. summer precipitation variability and North Atlantic Subtropical High (NASH) western ridge position. In contrast, the inability of G2 models to represent such linkage leads to their biases in simulating SE U.S. summer precipitation variability. According to our analysis, the ensemble projection of CMIP5 models suggests that under the Representative Concentration Pathway (RCP) 4.5 scenario, SE U.S. summer precipitation variability will intensify and that this intensification is more pronounced among G1 models. Our analysis further suggests that this intensification is most likely due to the projected pattern shift of the NASH western ridge in a warming climate. Under the RCP4.5 scenario, the NASH western ridge will extend further westward leading to more frequent occurrences of the northwestward and southwestward ridge patterns that are respectively related to dry and wet summers in the SE U.S. Consequently, more frequent occurrence of summer precipitation extremes would be expected over the SE U.S. in the future.