Regional modeling of surface-atmosphere interactions and their impact on Great Lakes hydroclimate

Abstract:

Land and water surfaces play a critical role in hydroclimate by supplying moisture to the atmosphere, yet the ability of climate models to capture their feedbacks with the atmosphere relative to large-scale transport is uncertain. To assess these land-lake-atmosphere feedbacks, we compare the controls on atmospheric moisture simulated by a Regional Climate Model (RegCM) with observations and reanalysis products for the Great Lakes region. Three 23-year simulations with different boundary conditions are performed to capture the hydroclimatic variability with synoptic conditions. RegCM simulates wetter winters and drier summers than observed by up to 31 and 21%, respectively. Moisture advection exhibits similar biases, suggesting the contribution of external sources, yet land surface fluxes account for nearly one third of summer precipitation. RegCM underestimates reanalysis evapotranspiration by nearly 50%; however, the reanalyses overestimate measurements at three flux towers by up to a factor of two. Neither RegCM nor the reanalyses capture the spatial variability in observed land evaporation, indicating a source of model uncertainty. In addition, RegCM underestimates the observed evaporation response to its atmospheric drivers such as vapor pressure deficit and temperature. Over the lakes, one model member overestimates convective precipitation caused by enhanced evaporation under warm lake surface temperatures, highlighting the need for accurate representation of lake temperature in the surface boundary condition. We conclude that climate models, including those driving reanalyses, underestimate the observed surface-atmosphere feedbacks and their influence on regional hydroclimate.