Essential Site Maintenance: Authorea-powered sites will be updated circa 15:00-17:00 Eastern on Tuesday 5 November.
There should be no interruption to normal services, but please contact us at [email protected] in case you face any issues.

loading page

The age of evapotranspiration: continental-scale lower-bound constraints from distributed water fluxes
  • +2
  • W. Jesse Hahm,
  • Dana Lapides,
  • Daniella Rempe,
  • Erica McCormick,
  • David N Dralle
W. Jesse Hahm
Simon Fraser University

Corresponding Author:[email protected]

Author Profile
Dana Lapides
Simon Fraser University
Author Profile
Daniella Rempe
University of Texas at Austinn
Author Profile
Erica McCormick
University of Texas at Austin
Author Profile
David N Dralle
Pacific Southwest Research Station, United States Forest Service
Author Profile

Abstract

Unlike streamflow, which can be sampled in aggregate at the catchment outlet, evapotranspiration (ET) is spatially dispersed, challenging large-scale age estimation. Here, we introduce an approach for constraining the age of ET via mass balance and present the minimum flux-weighted age of ET across the continental US using distributed, publicly available water flux datasets. The lower-bound constraint on ET age can be calculated by assuming that ET is preferentially sourced from the most recent precipitation through a last-in, first-out algorithm. From 2012-2017, ET was at least several months old across large areas of the western continental US, including in Mediterranean and (semi-)arid climate zones and shrub and evergreen needleleaf plant communities. The primary limitation of this approach is that it provides only a minimum flux-weighted average age to satisfy mass balance of outgoing fluxes; true ET fluxes are composed of distributions of ages and may be composed of much older water. The primary advantage of the approach is that flux timeseries of precipitation and ET are sufficient to constrain ET age, and model parameterization is unnecessary. ET ages can be used to validate tracer-aided and modeling approaches and inform studies of biogeochemistry, water-rock interactions, and plant water sourcing under drought.