Estimating Global Ecosystem Isohydry/Anisohydry Using Active and Passive Microwave Satellite Data

Yan Li, Kaiyu Guan, Pierre Gentine, Alexandra G. Konings, Frederick C. Meinzer, John S. Kimball, Xiangtao Xu, William R.L. Anderegg, Nate G. McDowell, Jordi Martinez-Vilalta, David G. Long, Stephen P. Good

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The concept of isohydry/anisohydry describes the degree to which plants regulate their water status, operating from isohydric with strict regulation to anisohydric with less regulation. Though some species level measures of isohydry/anisohydry exist at a few locations, ecosystem-scale information is still largely unavailable. In this study, we use diurnal observations from active (Ku-Band backscatter from QuikSCAT) and passive (X-band vegetation optical depth (VOD) from Advanced Microwave Scanning Radiometer on EOS Aqua) microwave satellite data to estimate global ecosystem isohydry/anisohydry. Here diurnal observations from both satellites approximate predawn and midday plant canopy water contents, which are used to estimate isohydry/anisohydry. The two independent estimates from radar backscatter and VOD show reasonable agreement at low and middle latitudes but diverge at high latitudes. Grasslands, croplands, wetlands, and open shrublands are more anisohydric, whereas evergreen broadleaf and deciduous broadleaf forests are more isohydric. The direct validation with upscaled in situ species isohydry/anisohydry estimates indicates that the VOD-based estimates have much better agreement than the backscatter-based estimates. The indirect validation with prior knowledge suggests that both estimates are generally consistent in that vegetation water status of anisohydric ecosystems more closely tracks environmental fluctuations of water availability and demand than their isohydric counterparts. However, uncertainties still exist in the isohydry/anisohydry estimate, primarily arising from the remote sensing data and, to a lesser extent, from the methodology. The comprehensive assessment in this study can help us better understand the robustness, limitation, and uncertainties of the satellite-derived isohydry/anisohydry estimates. The ecosystem isohydry/anisohydry has the potential to reveal new insights into spatiotemporal ecosystem response to droughts.

Original languageEnglish
Pages (from-to)3306-3321
Number of pages16
JournalJournal of Geophysical Research: Biogeosciences
Issue number12
StatePublished - Dec 2017


Y. L. and K. G. acknowledge the support from the NASA New Investigator Award (NNX16AI56G). P. G. acknowledge the NASA funding (NNX15AB30G). N. G. M. was sup ported by the Department of Energy, Office of Science, Next Generation Ecosystem Experiment-Tropics and Laboratory Directed Research and Development from Pacific Northwest National Laboratory. Y. L. would like to thank Jin Wu for providing com ments on the early version of the manuscript and also Jinyang Du for providing guidance of the VOD data. Y. L. thanks Bin Peng for giving com ments on the revised manuscript. We also thank three reviewers and the Editor for their insightful comments that significantly improved the manuscript. This paper was written in Authorea which is a cloud-based collaborative editor for research, and the manuscript is available at articles/189538. Data of this study are available at figshare (https://figshare. com/projects/Estimating_global_ ecosystem_iso_anisohydry_using_ active_and_passive_microwave_ satellite_data/19492). K. G. and Y. L. designed this study. Y. L. performed the study, and Y. L. and K. G. analyzed the data. W. R. L. A. provided idea of the GBIF analysis. P. G., A. G. K., F. C. M., J. S. K., X. X., W. R. L. A., N. G. M., J. M-V., D. G. L., and S. P. G. provided insights to interpreting the analysis and discussion. Y. L. and K. G. wrote the first draft of the manuscript, and all authors contributed to editing the manuscript.

FundersFunder number
National Aeronautics and Space AdministrationNNX16AI56G


    • AMSR-E
    • QuikSCAT
    • isohydry/anisohydry
    • radar backscatter
    • vegetation optical depth


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