Regional Models Project Greater Drought Resilience in U.S. Southwest in Warmer Climate
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’s 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 region’s water cycle is dominated by winter storms that maintain a positive annual net precipitation (precipitation minus evapotranspiration). The research team found that the regional models simulate greater transport of moisture eastward over the mountains because the air flow over the topographically complex mountains is better resolved. Under global warming, this enables the RCMs to capture a response that allows more moisture to converge on the windward side of the mountains. 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. Because the RCMs with their sharper topographic relief more accurately simulate enhanced moisture convergence, they indicate that the SW is less susceptible to experience drought compared to GCMs.
Gao, Y., L. R. Leung, E. P. Salathé Jr., F. Dominguez, B. Nijssen, and D. P. 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.