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Global Relationships Among Traditional Reflectance Vegetation Indices (NDVI and NDII), Evapotranspiration (ET), and Soil Moisture Variability on Weekly Time ScalesMonitoring the effects of water availability on vegetation globally using satellites is important for applications such as drought early warning, precision agriculture, and food security as well as for more broadly understanding relationships between water and carbon cycles. In this global study, we examine how quickly several satellite-based indicators, assumed to have relationships with water availability, respond, on timescales of days to weeks, in comparison with variations in root-zone soil moisture (RZM) that extends to about 1 m depth. The satellite indicators considered are the normalized difference vegetation and infrared indices (NDVI and NDII, respectively) derived from reflectances obtained with moderately wide (20–40 nm) spectral bands in the visible and near-infrared (NIR) and evapotranspiration (ET) estimated from thermal infrared observations and normalized by a reference ET. NDVI is primarily sensitive to chlorophyll contributions and vegetation structure while NDII may contain additional information on water content in leaves and canopy. ET includes both the loss of root zone soil water through transpiration (modulated by stomatal conductance) as well as evaporation from bare soil. We find that variations of these satellite-based drought indicators on time scales of days to weeks have significant correlations with those of RZM in the same water-limited geographical locations that are dominated by grasslands, shrublands, and savannas whose root systems are generally contained within the 1 m RZM layer. Normalized ET interannual variations show generally a faster response to water deficits and enhancements as compared with those of NDVI and NDII, particularly in sparsely vegetated regions.
Document ID
20190002331
Acquisition Source
Goddard Space Flight Center
Document Type
Accepted Manuscript (Version with final changes)
External Source(s)
Authors
Joanna Joiner ORCID(Goddard Space Flight Center Greenbelt, Maryland, United States)
Yasuko Yoshida ORCID(Science Systems and Applications (United States) Lanham, Maryland, United States)
Martha Anderson (United States Department of Agriculture Washington D.C., District of Columbia, United States)
Thomas Holmes ORCID(Goddard Space Flight Center Greenbelt, Maryland, United States)
Christopher Hain (Marshall Space Flight Center Redstone Arsenal, Alabama, United States)
Rolf Reichle ORCID(Goddard Space Flight Center Greenbelt, Maryland, United States)
Randal Koster (Goddard Space Flight Center Greenbelt, Maryland, United States)
Elizabet Middleton (Goddard Space Flight Center Greenbelt, Maryland, United States)
Fan-Wei Zeng (Science Systems and Applications (United States) Lanham, Maryland, United States)
Date Acquired
April 11, 2019
Publication Date
October 24, 2018
Publication Information
Publication: Remote Sensing of Environment
Publisher: Elsevier
Volume: 219
Issue Publication Date: December 1, 2018
ISSN: 0034-4257
e-ISSN: 1879-0704
DOI: doi:10.1016/j.rse.2018.10.020
Subject Category
Earth Resources And Remote Sensing
Report/Patent Number
GSFC-E-DAA-TN67177
ISSN: 0034-4257
E-ISSN: 1879-0704
Report Number: GSFC-E-DAA-TN67177
Funding Number(s)
CONTRACT_GRANT: NNG17HP01C
PROJECT: SCMD-PlanetaryScience_982745
Distribution Limits
Public
Copyright
Use by or on behalf of the US Gov. Permitted.
Technical Review
NASA Peer Committee

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