Evap’Eau project: Estimating actual evapotranspiration from remote sensing in Senegal and Niger

This project, financed by ICIREWARD UNESCO center of Montpellier, is part of his WP2 "Large-scale hydrosystem processes to assess changes in the availability and quality of water resources caused by climate change" of the UNESCO centre's project. It also includes a skills transfer component for permanent or future researchers and training for doctoral students and students.

Evapotranspiration (ET) is a surface process that ensures the recycling of water and the redistribution of incident energy to the near atmosphere. In this way, it links the major continental water and energy cycles and is a major variable of interest for studies on the management and monitoring of hydro(geo)logical and plant resources (closure of water balances, monitoring of water tables, irrigation management, crop forecasting, etc.). This is all the more the case in West Africa, where ET accounts for more than 85% of rainfall (Velluet et al., 2014) and where the human pressures on the environment in terms of land use and occupation are real societal issues. These significant changes in the territory, coupled with the current and future effects of climate change, exacerbate the pressures on sensitive ecosystems where the balance of natural resources is already fragile. The proposal of methodologies to monitor and anticipate changes in green water resources (including ET) is therefore a major scientific challenge.

Satellite data acquired in the thermal infrared range provide access to a key energy balance variable, i.e. the surface temperature (ST). This variable is correlated, depending on the intensity of water stress, with ET. Over the last few decades, several algorithms have been proposed to exploit this link, and consequently to estimate ET from ST. In spite of this popularity, the current challenge is the ability of these algorithms to generate sufficiently robust, accurate and frequent products to establish annual-scale balances.

This project aims to assess the potential of the different types of satellite-based ET approaches currently applied in West Africa, not only by comprehensively reviewing and testing the ET products available in the region, but also by actively contributing to the generation of new and more reliable products.