Accuracy of the Temperature-Vegetation Dryness Index using MODIS under water-limited vs. energy-limited evapotranspiration conditions

Monica Garcia, N. Fernández, L. Villagarcía, F. Domingo, J. Puigdefábregas, Inge Sandholt

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    Abstract

    Water deficit indices based on the spatial relationship between surface temperature (Ts) and NDVI, known as triangle approaches, are widely used for drought monitoring. However, their application has been recently questioned when the main factor limiting evapotranspiration is energy. Even though water is the main control in dryland ecosystems, these can also undergo periods of energy and temperature limitation. In this paper we aimed to: (i) evaluate the TVDI (Temperature-Vegetation Dryness Index) to estimate water deficits (e.g. ratio between actual and potential evapotranspiration), and heat surface fluxes using MODIS data; and (ii) provide insights about the factors most affecting the accuracy of results. Factors considered included the type of climatic control on evapotranspiration, λE, (i.e. water-limited vs. energy-limited), the quality of Tair estimates, the heterogeneity of land cover types and climatic variables in the region, or the algorithm to extract hydrological boundaries from the images. The TVDI was compared with eddy covariance (EC) data from two shrublands with different climatic controls for λE in South Spain. Evaluations showed that it could be used to estimate the water deficit when water was the main limiting factor (R=0.81-0.88; Mean Average Error, MAE=0.16-0.17) but not in energy-limited situations (R
    Original languageEnglish
    JournalRemote Sensing of Environment
    Volume149
    Pages (from-to)100-117
    Number of pages18
    ISSN0034-4257
    DOIs
    Publication statusPublished - 2014

    Keywords

    • Triangle approach
    • Ecohydrology
    • Water stress
    • Evapotranspiration
    • Surface energy balance
    • Ecosystem controls
    • Land surface temperature
    • Eddy covariance
    • Algorithms
    • Atmospheric temperature
    • Ecosystems
    • Energy balance
    • Estimation
    • Heat flux
    • Interfacial energy
    • Radiometers
    • Surface measurement
    • Vegetation
    • Eco-hydrology
    • Ecosystem control

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