Image courtesy of Washington University in St. Louis
Distribution of the wintertime differences in the westerly transient moisture flux – From Gao Y, LR Leung, EP Salathé Jr, F Dominguez, B Nijssen, and DP Lettenmaier, 2012. “Moisture Flux Convergence in Regional and Global Climate Models: Implications for Droughts in the Southwestern United States under Climate Change.” Geophysical Research Letters 39:L09711. [DOI: 10.1029/2012GL051560].
Regional climate models (RCM) simulate greater transport of moisture eastward over the mountains because the air flow over the topographically complex mountains is better resolved. This enables the RCMs to capture a response that allows more moisture to converge on the windward side of the mountains.
Regional Climate Models, with their sharper topographic relief, more accurately simulate enhanced moisture convergence and indicate that the southwest is less susceptible to experience drought compared to predictions from General Circulation Models (GCMs).
Getting an accurate projection of water cycle changes for the southwestern United States (SW) is becoming increasingly more urgent in light of regional drought trends and changes in the Colorado River flow. A research team, including a DOE scientist from Pacific Northwest National Laboratory, analyzed the future climate from four pairs of regional and global climate models (RCMs and GCMs). The water cycle of the region is dominated by winter storms that maintain a positive annual net precipitation (precipitation minus evapotranspiration). The analysis shows that compared to GCMs, RCMs simulate enhanced transient moisture convergence in the SW, although both robustly simulate large-scale drying due to enhanced moisture divergence by the divergent mean flow in a warmer climate.
Dr. Dennis Lettenmaier
Washington University in St. Louis
Basic Research: DOE Office of Science, Office of Biological and Environmental Research
Gao Y, LR Leung, EP Salathé Jr, F Dominguez, B Nijssen, and DP Lettenmaier, 2012. “Moisture Flux Convergence in Regional and Global Climate Models: Implications for Droughts in the Southwestern United States under Climate Change.” Geophysical Research Letters 39:L09711. DOI: 10.1029/2012GL051560. http://www.agu.org/pubs/crossref/2012/2012GL051560.shtml.
University, DOE Laboratory