Assessing climate change impacts for DoD installations in the Southwest United States during the warm season: Progress toward characterizing the historical record

The Southwest U.S. is strategically important in that it houses some of the most spatially expansive and important military installations in the country. Though the main climate change concern in the Southwest from the civilian perspective is future water resource availability, the greater concern from the perspective of the Department of Defense is the possible increase in extreme weather events. A likely consequence of climate change is an increase in frequency and/or intensity of thunderstorms during period of the North American monsoon in late summer. Current global climate models or global atmospheric reanalyses projection are inadequate to represent the monsoon as a climatological feature, much less individual thunderstorms that would cause severe weather. High resolution dynamical downscaling is a viable approach to address the precipitation intensity issue. In this research, we dynamically downscale an atmospheric reanalysis and select "well performing" IPCC global climate models used in CMIP3 and CMIP5 with a regional climate model (RCM). Severe weather events are first identified in long-term RCM simulations (at a 35-km grid spacing) by consideration of thermodynamic and dynamic criteria used by operational forecasters. Next, these identified severe weather events are simulated at a convective-resolving (2-km) grid spacing, as in a short-term numerical weather prediction model. At this stage of the project, we have developed the methodology for identifying severe weather events in the RCM simulations and have simulated severe weather events within the historical record (1950-present). In particular, we emphasize how the model is representing organized, propagating convection.