Evaluating the water cycle over CONUS at the watershed scale for the Energy Exascale Earth System Model version 1 (E3SMv1) across resolutions
The water cycle is an important component of the earth system and it plays a key role in many facets of society, including energy production, agriculture, and human health and safety. Earth system models have been an important tool for deepening our understanding and testing hypotheses related to the water cycle. Continued advances in computing power have enabled earth system models to resolve features important to the water cycle that lower resolution models often fail to capture. In this study, the Energy Exascale Earth System Model (E3SM) is run with low- and high-resolution configurations --- as established by the HighResMIP protocol --- to evaluate the atmospheric and terrestrial water budgets over the conterminous United States (CONUS) at the watershed scale. The water cycle slows down in the HR experiment relative to the LR, with decreasing fluxes of precipitation, evapotranspiration, atmospheric moisture convergence, and runoff. The reductions in these terms exacerbate biases for some watersheds, while reducing them in others. The most pronounced changes to the water cycle come from reductions in evapotranspiration and precipitation. The current simulations do not allow for disentangling responses to the remote resolution increase from responses owing to the local resolution increase, but future E3SM research directions are well-suited for follow-up analyses. Additional exploratory metrics are examined to better understand features anticipated to have sensitivity to resolution such as snowpack, and precipitation and streamflow extremes.