Evaluating the water cycle over CONUS at the watershed scale for the
Energy Exascale Earth System Model version 1 (E3SMv1) across resolutions
Abstract
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. In this study, the Energy
Exascale Earth System Model version 1 (E3SMv1) is run with
low-resolution (roughly 110 km) and high-resolution (roughly 25 km)
configurations — as established by the High Resolution Model
Intercomparison Project protocol — to evaluate the atmospheric and
terrestrial water budgets over the conterminous United States (CONUS) at
the large 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. For example, precipitation biases are
exacerbated at HR over the Eastern and Central CONUS watersheds, while
precipitation biases are reduced at HR over the Western CONUS
watersheds. The most pronounced changes to the water cycle come from
reductions in precipitation and evapotranspiration, the latter of which
results from decreases in evaporative fraction. While the HR simulation
is warmer than the LR, moisture convergence decreases despite the
increased atmospheric water vapor, suggesting circulation biases are an
important factor. Additional exploratory metrics show improvements to
water cycle extremes (both in precipitation and streamflow), fractional
contributions of different storm types to total precipitation, and
mountain snowpack.