Remotely sensed soil moisture can capture dynamics relevant to plant water uptake

Authors: FELDMAN, A.F. - National Aeronautics And Space Administration (NASA) - Johnson Space Center; SHORT GIANOTTI, D.J. - Massachusetts Institute Of Technology; DONG, J. - Massachusetts Institute Of Technology; AKBAR, R. - Massachusetts Institute Of Technology; Crow, Wade; MCCOLL, K.A. - Harvard University; KONINGS, SA.G. - Stanford University; NIPPERT, J.B. - Kansas State University; TUMBER-DÁVILA, S.J. - Harvard University; HOLBROOK, N.M. - Harvard University; ROCKWELL, F.E. - Harvard University; Scott, Russell - Russ; REICHLE, R - National Aeronautics And Space Administration (NASA); CHATTERJEE, A. - Jet Propulsion Laboratory; JOINER, J. - Jet Propulsion Laboratory; POULTER, B. - National Aeronautics And Space Administration (NASA); ENTEKHABI, D - Massachusetts Institute Of Technology

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2023
Publication Date: 2/15/2023
Citation: Feldman, A., Short Gianotti, D., Dong, J., Akbar, R., Crow, W.T., McColl, K., Konings, S., Nippert, J., Tumber-Dávila, S., Holbrook, N., Rockwell, F., Scott, R.L., Reichle, R.H., Chatterjee, A., Joiner, J., Poulter, B., Entekhabi, D. 2023. Remotely sensed soil moisture can capture dynamics relevant to plant water uptake. Water Resources Research. 59(2). Article e2022WR033814. https://doi.org/10.1029/2022WR033814.
DOI: https://doi.org/10.1029/2022WR033814

Interpretive Summary: A common viewpoint across the Earth science community is that global soil moisture estimates from satellite measurements represent moisture only in the shallow soil layers (0-5 cm) and are of limited value for studying global land ecosystems because plants use water from deeper root zones. Here, we argue that such a viewpoint is flawed for two reasons. First, the theory behind satellite soil moisture measurements indicate that measurements are typically representative of soil moisture within at least the top 15-25 cm, or 3-5 times deeper than commonly thought. Second, in reviewing studies of plant water uptake, we find a global prevalence of vegetation that primarily draws moisture from these upper soil layers. This is especially true for grasslands and croplands covering more than a third of global vegetated surfaces. While shrub and tree species tend to draw deeper soil moisture, these plants often still preferentially or seasonally draw water from the upper soil layers. Therefore, satellite soil moisture estimates are more relevant to global vegetation water uptake than commonly appreciated, and we encourage their application across hydrological studies.

Technical Abstract: A common viewpoint across the Earth science community is that global soil moisture estimates from satellite L-band (1.4 GHz) measurements represent moisture only in the shallow soil layers (0-5 cm) and are of limited value for studying global terrestrial ecosystems because plants use water from deeper rootzones. Here, we argue that such a viewpoint is flawed for two reasons. First, microwave soil emission theory and statistical considerations of vertically correlated soil moisture information together indicate that L-band measurements are typically representative of soil moisture within at least the top 15-25 cm, or 3-5 times deeper than commonly thought. Second, in reviewing isotopic tracer field studies of plant water uptake, we find a global prevalence of vegetation that primarily draws moisture from these upper soil layers. This is especially true for grasslands and croplands covering more than a third of global vegetated surfaces. While shrub and tree species tend to draw deeper soil moisture, these plants often still preferentially or seasonally draw water from the upper soil layers. Therefore, L-band satellite soil moisture estimates are more relevant to global vegetation water uptake than commonly appreciated, and we encourage their application across terrestrial hydrosphere and biosphere studies.