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Detecting forest response to droughts with global observations of vegetation water content

Konings, Alexandra G. and Saatchi, Sassan S. and Frankenberg, Christian and Keller, Michael and Leshyk, Victor and Anderegg, William R. L. and Humphrey, Vincent and Matheny, Ashley M. and Trugman, Anna and Sack, Lawren and Agee, Elizabeth and Barnes, Mallory L. and Binks, Oliver and Cawse‐Nicholson, Kerry and Christoffersen, Bradley O. and Entekhabi, Dara and Gentine, Pierre and Holtzman, Nataniel M. and Katul, Gabriel G. and Liu, Yanlan and Longo, Marcos and Martinez‐Vilalta, Jordi and McDowell, Nate and Meir, Patrick and Mencuccini, Maurizio and Mrad, Assaad and Novick, Kimberly A. and Oliveira, Rafael S. and Siqueira, Paul and Steele‐Dunne, Susan C. and Thompson, David R. and Wang, Yujie and Wehr, Richard and Wood, Jeffrey D. and Xu, Xiangtao and Zuidema, Pieter A. (2021) Detecting forest response to droughts with global observations of vegetation water content. Global Change Biology, 27 (23). pp. 6005-6024. ISSN 1354-1013. doi:10.1111/gcb.15872.

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Droughts in a warming climate have become more common and more extreme, making understanding forest responses to water stress increasingly pressing. Analysis of water stress in trees has long focused on water potential in xylem and leaves, which influences stomatal closure and water flow through the soil-plant-atmosphere continuum. At the same time, changes of vegetation water content (VWC) are linked to a range of tree responses, including fluxes of water and carbon, mortality, flammability, and more. Unlike water potential, which requires demanding in situ measurements, VWC can be retrieved from remote sensing measurements, particularly at microwave frequencies using radar and radiometry. Here, we highlight key frontiers through which VWC has the potential to significantly increase our understanding of forest responses to water stress. To validate remote sensing observations of VWC at landscape scale and to better relate them to data assimilation model parameters, we introduce an ecosystem-scale analog of the pressure–volume curve, the non-linear relationship between average leaf or branch water potential and water content commonly used in plant hydraulics. The sources of variability in these ecosystem-scale pressure-volume curves and their relationship to forest response to water stress are discussed. We further show to what extent diel, seasonal, and decadal dynamics of VWC reflect variations in different processes relating the tree response to water stress. VWC can also be used for inferring below-ground conditions—which are difficult to impossible to observe directly. Lastly, we discuss how a dedicated geostationary spaceborne observational system for VWC, when combined with existing datasets, can capture diel and seasonal water dynamics to advance the science and applications of global forest vulnerability to future droughts.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemData
Konings, Alexandra G.0000-0002-2810-1722
Saatchi, Sassan S.0000-0001-8524-4917
Frankenberg, Christian0000-0002-0546-5857
Keller, Michael0000-0002-0253-3359
Anderegg, William R. L.0000-0001-6551-3331
Humphrey, Vincent0000-0002-2541-6382
Matheny, Ashley M.0000-0002-9532-7131
Trugman, Anna0000-0002-7903-9711
Sack, Lawren0000-0002-7009-7202
Agee, Elizabeth0000-0002-2331-3056
Barnes, Mallory L.0000-0001-8528-6981
Binks, Oliver0000-0002-6291-3644
Cawse‐Nicholson, Kerry0000-0002-0510-4066
Christoffersen, Bradley O.0000-0002-4890-9999
Entekhabi, Dara0000-0002-8362-4761
Gentine, Pierre0000-0002-0845-8345
Holtzman, Nataniel M.0000-0002-0585-9928
Katul, Gabriel G.0000-0001-9768-3693
Liu, Yanlan0000-0001-5129-6284
Longo, Marcos0000-0001-5062-6245
Martinez‐Vilalta, Jordi0000-0002-2332-7298
McDowell, Nate0000-0002-2178-2254
Meir, Patrick0000-0002-2362-0398
Mencuccini, Maurizio0000-0003-0840-1477
Mrad, Assaad0000-0003-4922-4446
Novick, Kimberly A.0000-0002-8431-0879
Oliveira, Rafael S.0000-0002-6392-2526
Siqueira, Paul0000-0001-5781-8282
Steele‐Dunne, Susan C.0000-0002-8644-3077
Thompson, David R.0000-0003-1100-7550
Wang, Yujie0000-0002-3729-2743
Wehr, Richard0000-0002-0806-9390
Wood, Jeffrey D.0000-0001-6422-2882
Xu, Xiangtao0000-0002-9402-9474
Zuidema, Pieter A.0000-0001-8100-1168
Additional Information:© 2021 The Authors. Global Change Biology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Issue Online: 01 November 2021; Version of Record online: 25 September 2021; Accepted manuscript online: 03 September 2021; Manuscript accepted: 23 August 2021; Manuscript received: 19 April 2021. We are grateful to Kara Skye Gibson for assisting Victor Leshyk with the creation of Figures 1, 3, and 5. We also thank our many collaborators for discussions. The outlines of this work were developed in the “Sensing Forest Water Dynamics from Space: Towards Predicting the Earth System Response to Droughts” study, which was initiated and supported by the W.M. Keck Institute for Space Studies. LS was supported by NSF grant DEB-2017949. AGK was supported by NASA Terrestrial Ecology award 80NSSC18K0715. EA was supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. The research carried out at the Jet Propulsion Laboratory, California Institute of Technology, was under a contract with the National Aeronautics and Space Administration. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-100800OR22725. Data Availability Statement: QuikScat data shown in Figure 2 are available from the NASA PODAAC at The authors declare no conflicts of interest.
Group:Keck Institute for Space Studies
Funding AgencyGrant Number
Keck Institute for Space Studies (KISS)UNSPECIFIED
Department of Energy (DOE)DE-AC05-100800OR22725
Subject Keywords:drought response; drought-induced tree mortality; microwave remote sensing; pressure–volume; vegetation optical depth; vegetation water content; water potential
Issue or Number:23
Record Number:CaltechAUTHORS:20211117-215532673
Persistent URL:
Official Citation:Konings, A. G., Saatchi, S. S., Frankenberg, C., Keller, M., Leshyk, V., Anderegg, W. R. L., Humphrey, V., Matheny, A. M., Trugman, A., Sack, L., Agee, E., Barnes, M. L., Binks, O., Cawse-Nicholson, K., Christoffersen, B. O., Entekhabi, D., Gentine, P., Holtzman, N. M., Katul, G. G., … Zuidema, P. A. (2021). Detecting forest response to droughts with global observations of vegetation water content. Global Change Biology, 27, 6005–6024.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111936
Deposited By: Tony Diaz
Deposited On:17 Nov 2021 23:35
Last Modified:17 Nov 2021 23:35

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