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Open AccessArticle

Tracking Ecosystem Water Use Efficiency of Cropland by Exclusive Use of MODIS EVI Data

1
Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
2
State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 100101, China
3
Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN 55108, USA
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Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
5
Key Laboratory of Poyang Lake Wetland and Watershed Research (Jiangxi Normal University), Ministry of Education, Nanchang 330022, China
*
Authors to whom correspondence should be addressed.
Academic Editors: Pablo J. Zarco-Tejada, Yoshio Inoue and Prasad S. Thenkabail
Remote Sens. 2015, 7(9), 11016-11035; https://doi.org/10.3390/rs70911016
Received: 28 July 2015 / Revised: 13 August 2015 / Accepted: 20 August 2015 / Published: 26 August 2015
One of the most important linkages that couple terrestrial carbon and water cycles is ecosystem water use efficiency (WUE), which is relevant to the reasonable utilization of water resources and farming practices. Eddy covariance techniques provide an opportunity to monitor the variability in WUE and can be integrated with Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Scaling up in situ observations from flux tower sites to large areas remains challenging and few studies have been reported on direct estimation of WUE from remotely-sensed data. This study examined the main environmental factors driving the variability in WUE of corn/soybean croplands, and revealed the prominent role of solar radiation and temperature. Time-series of MODIS-derived enhanced vegetation indices (EVI), which are proxies for the plant responses to environmental controls, were also strongly correlated with ecosystem WUE, thereby implying great potential for remote quantification. Further, both performance of the indirect MODIS-derived WUE from gross primary productivity (GPP) and evapotranspiration (ET), and the direct estimates by exclusive use of MODIS EVI data were evaluated using tower-based measurements. The results showed that ecosystem WUE were overpredicted at the beginning and ending of crop-growth periods and severely underestimated during the peak periods by the indirect estimates from MODIS products, which was mainly attributed to the error source from MODIS GPP. However, a simple empirical model that is solely based on MODIS EVI data performed rather well to capture the seasonal variations in WUE, especially for the growing periods of croplands. Independent validation at different sites indicates the method has potential for broad application. View Full-Text
Keywords: water use efficiency; cropland; MODIS; vegetation index; GPP; ET water use efficiency; cropland; MODIS; vegetation index; GPP; ET
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Tang, X.; Li, H.; Griffis, T.J.; Xu, X.; Ding, Z.; Liu, G. Tracking Ecosystem Water Use Efficiency of Cropland by Exclusive Use of MODIS EVI Data. Remote Sens. 2015, 7, 11016-11035.

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