EGU General Assembly 2020
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Evaluating Validity of Bouchet-Morton Complementary Relationship at Regional Scale through Terrestrial Evapotranspiration derived using Remote Sensing Platform and Land Surface Models

Swapan Kumar Masanta1 and Srinivas Venkata Vemavarapu1,2
Swapan Kumar Masanta and Srinivas Venkata Vemavarapu
  • 1Department of Civil Engineering, Indian Institute of Science, India (
  • 2Interdisciplinary Center for Water Research (ICWaR), Indian Institute of Science, India (

Evapotranspiration is one of the most important components of the terrestrial hydrological cycle, which depicts atmospheric water demand and accounts for loss of more than 60% land-surface precipitation globally. Decrease in potential/reference evapotranspiration (ETp), despite significant increase in near-surface air temperature is reported at many locations across the world in the recent decades. This counter-intuitive phenomenon known as evaporation-paradox could be attributed to decrease in net solar radiation and/or wind speed and/or increase in terrestrial evapotranspiration (ETa). Gaining insight into evaporation-paradox requires understanding complex interaction between land-plant-atmosphere systems. Bouchet–Morton complementary relationship (CR) hypothesizes that at regional scale there exists a feedback mechanism between ETa and ETp for homogeneous surfaces having low advection of heat and moisture. It postulates that increase in regional ETa consumes energy thereby cooling and humidifying the overpassing air, which would result in reduction of regional ETp. Similarly, available excess energy which is not used for evapotranspiration (due to decrease in regional ETa) would result in an increase of regional ETp through warming and drying of the atmosphere. Recent improvements in remote sensing technology provide scope to quantify ETa and use it for evaluating validity of CR at regional scale to discern the possible cause for evaporation-paradox. If the CR is valid for a region, models could be developed to estimate regional ETa using ETp estimated using regional values of its predictor hydro-climate variables. Prior studies on Indian subcontinent found evidence of evaporation-paradox at various sites scattered widely in space. But there is lack of attempts to establish existence of the paradox at regional scale and discern possible cause(s) for the same. In this backdrop, research is envisaged to (i) form homogeneous ETa and ETp regions in India using a novel dynamic fuzzy clustering approach, (ii) investigate existence of evaporation-paradox in each of those regions, and (iii) identify validity of CR and discern possible cause(s) for the paradox, if evident. ETa is typically estimated from eddy covariance flux towers, remote sensing techniques, or computed from land surface models which often suffer from limitations of scale and data. Uncertainty arising due to the use of (i) two different hydro-climate re-analysis datasets for ETp estimation, and (ii) one remote sensing based and three land surface model derived ETa products is assessed. The dynamic clustering approach yielded 18 homogeneous ETp regions and 30 homogeneous ETa regions in India. The role of CR on evaporation-paradox was evident in eight regions. The effect of vegetation and climate on CR is studied at regional scale using NDVI (normalized difference vegetation index). In addition, existence of CR hypotheses is verified in 405 major river basins of different sizes located in diverse climate regions across the globe using combination of several model derived and remotely sensed ETa and ETp datasets. This study is of significance, as evidence of the effect of location, vegetation and climate on CR at regional scale gives scope for developing region-specific models to arrive at ETa estimates directly from ETp which could be estimated/forecasted from hydro-climate variables.

How to cite: Masanta, S. K. and Venkata Vemavarapu, S.: Evaluating Validity of Bouchet-Morton Complementary Relationship at Regional Scale through Terrestrial Evapotranspiration derived using Remote Sensing Platform and Land Surface Models , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-910,, 2019

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