Changes in Intense Rainfall Events over the Central United States in AOGCM-Driven Regional Climate Model Simulations

We have evaluated trends in extreme precipitation frequency for the central United States (Groisman et al. 2012) using atmosphere-ocean global climate model (AOGCM) driven regional climate simulations. Nested regional climate model simulations were conducted using RegCM4.4 over the CORDEX-North America domain with 50 km grid spacing. Initial and lateral boundary conditions are taken from the HadGEM2-ES and GFDL-ESM2M AOGCMs (for RCP8.5 emissions scenario) to simulate present and future climate (1951-2098). For each run, RegCM4 uses three different convection schemes: Emanuel scheme, Grell scheme, and Mixed scheme which uses the Emanuel scheme over water and Grell over land.

Current findings show the regional climate simulations are of the same magnitude of average frequency for heavy ( 25.4-76.2 mm/day), and extreme (154.9+ mm/day) precipitation events while very heavy events (76.2+ mm/day) were less frequent by an order of magnitude. For current and recent past climate (1951-2005), frequency of precipitation events is similar in both HadGEM2-ES and GFDL-ESM2M AOGCM-driven regional climate simulations with most variation due to the convection scheme being used. Initial results seem to exhibit similar trends in the increase of frequency for each precipitation event as is seen in observations. In accordance with Groisman et al. (2012), preliminary findings also show months during the cold season had more frequent heavy events in comparison to very heavy and extreme events while months during the warm season had more frequent very heavy and extreme events in comparison to heavy events. Further analysis will better determine the correlation and accuracy of these regional climate simulations.