Department Seminar: Alex Hall

Title: Thermodynamic Control of Hydroclimate Change in the Western United States and Its Consequences

Abstract: Regional hydroclimate projections are often viewed as deeply uncertain due to differences in simulated atmospheric circulation responses, yet many key features of projected change in the Western United States, including extreme precipitation intensification, snowpack loss, and shifts in runoff timing, are remarkably robust across models and downscaling approaches. In this talk, I argue that this robustness arises because the forced response of the regional hydroclimate system is primarily thermodynamically controlled. Using dynamical downscaling experiments that isolate thermodynamic and dynamical contributions, along with moisture budget diagnostics, I show that much of the regional response can be reproduced from thermodynamic forcing alone, with circulation changes playing a secondary, modulating role. I then synthesize results across multiple components of the water cycle to show how this framework explains both robust signals and key uncertainties. I suggest that similar thermodynamic constraints may govern hydroclimate responses in other regions, even where evidence remains more limited. Finally, I discuss implications of this framework for water resources and wildfire, where thermodynamically driven changes in moisture availability and variability propagate through the system to shape risks.