Comparing Evapotranspiration from Eddy Covariance Measurements, Water Budgets, Remote Sensing, and Land Surface Models over Canada

Shusen Wang Canada Centre for Mapping and Earth Observation, Natural Resources Canada, Ottawa, Ontario, Canada

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Ming Pan Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey

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Qiaozhen Mu College of Forestry and Conservation, University of Montana, Missoula, Montana
Department of Geographical Sciences, University of Maryland, College Park, College Park, Maryland

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Xiaoying Shi Environmental Sciences Division, and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, Tennessee

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Jiafu Mao Environmental Sciences Division, and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, Tennessee

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Christian Brümmer Thünen Institute of Climate-Smart Agriculture, Braunschweig, Germany

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Rachhpal S. Jassal Biometeorology and Soil Physics Group, The University of British Columbia, Vancouver, British Columbia, Canada

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Praveena Krishnan Atmospheric Turbulence and Diffusion Division, NOAA, Oak Ridge, Tennessee
Oak Ridge Associated Universities, Oak Ridge, Tennessee

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Junhua Li Canada Centre for Mapping and Earth Observation, Natural Resources Canada, Ottawa, Ontario, Canada

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T. Andrew Black Biometeorology and Soil Physics Group, The University of British Columbia, Vancouver, British Columbia, Canada

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Abstract

This study compares six evapotranspiration ET products for Canada’s landmass, namely, eddy covariance EC measurements; surface water budget ET; remote sensing ET from MODIS; and land surface model (LSM) ET from the Community Land Model (CLM), the Ecological Assimilation of Land and Climate Observations (EALCO) model, and the Variable Infiltration Capacity model (VIC). The ET climatology over the Canadian landmass is characterized and the advantages and limitations of the datasets are discussed. The EC measurements have limited spatial coverage, making it difficult for model validations at the national scale. Water budget ET has the largest uncertainty because of data quality issues with precipitation in mountainous regions and in the north. MODIS ET shows relatively large uncertainty in cold seasons and sparsely vegetated regions. The LSM products cover the entire landmass and exhibit small differences in ET among them. Annual ET from the LSMs ranges from small negative values to over 600 mm across the landmass, with a countrywide average of 256 ± 15 mm. Seasonally, the countrywide average monthly ET varies from a low of about 3 mm in four winter months (November–February) to 67 ± 7 mm in July. The ET uncertainty is scale dependent. Larger regions tend to have smaller uncertainties because of the offset of positive and negative biases within the region. More observation networks and better quality controls are critical to improving ET estimates. Future techniques should also consider a hybrid approach that integrates strengths of the various ET products to help reduce uncertainties in ET estimation.

Denotes Open Access content.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JHM-D-14-0189.s1.

Earth Science Sector Contribution Number 20140252.

Corresponding author address: Shusen Wang, Canada Centre for Mapping and Earth Observation, National Resources Canada, 560 Rochester St., Ottawa ON K1A 0E4, Canada. E-mail: shusen.wang@nrcan.gc.ca

Abstract

This study compares six evapotranspiration ET products for Canada’s landmass, namely, eddy covariance EC measurements; surface water budget ET; remote sensing ET from MODIS; and land surface model (LSM) ET from the Community Land Model (CLM), the Ecological Assimilation of Land and Climate Observations (EALCO) model, and the Variable Infiltration Capacity model (VIC). The ET climatology over the Canadian landmass is characterized and the advantages and limitations of the datasets are discussed. The EC measurements have limited spatial coverage, making it difficult for model validations at the national scale. Water budget ET has the largest uncertainty because of data quality issues with precipitation in mountainous regions and in the north. MODIS ET shows relatively large uncertainty in cold seasons and sparsely vegetated regions. The LSM products cover the entire landmass and exhibit small differences in ET among them. Annual ET from the LSMs ranges from small negative values to over 600 mm across the landmass, with a countrywide average of 256 ± 15 mm. Seasonally, the countrywide average monthly ET varies from a low of about 3 mm in four winter months (November–February) to 67 ± 7 mm in July. The ET uncertainty is scale dependent. Larger regions tend to have smaller uncertainties because of the offset of positive and negative biases within the region. More observation networks and better quality controls are critical to improving ET estimates. Future techniques should also consider a hybrid approach that integrates strengths of the various ET products to help reduce uncertainties in ET estimation.

Denotes Open Access content.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JHM-D-14-0189.s1.

Earth Science Sector Contribution Number 20140252.

Corresponding author address: Shusen Wang, Canada Centre for Mapping and Earth Observation, National Resources Canada, 560 Rochester St., Ottawa ON K1A 0E4, Canada. E-mail: shusen.wang@nrcan.gc.ca

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