Unravelling groundwater contributions to evapotranspiration and constraining water fluxes in a high-elevation catchment

We used the eddy covariance method to estimate ET from years 2017 through 2019 at a saturated, riparian end-member site. Owing to complexities in near surface atmospheric structure such as stable boundary layers over snowpack and shallow terrain driven flow from surrounding landscape features, energy flux and ET estimates were limited to the warm season when energy closure residuals from the eddy-covariance system were reliably less than 30%, a threshold commonly used in eddy covariance energy flux estimation.

The resulting ET estimations are useful for constraining water budget estimates at this energy-limited site, which uses groundwater for up to 84% of ET in the summer months. We also compared East River ET magnitudes and seasonality to two other flux towers (Niwot Ridge, CO and Valles Caldera, NM), located in the Rocky Mountains. These data are useful for constraining ET estimates in similar end-member locations across the East River Catchment.

Our results show that groundwater-fed ET is a significant component of the water balance and groundwater may supply riparian ET even during low-snow years.