INFLLUNCE OF IRRIGATION ON THE BIAS BETWEEN ORCHIDEE AND FLUXCOM EVAPOTRANSPIRATION PRODUCTS

Terrestrial Evapotranspiration (ET) is a key component of the surface energy balance and it is the second largest component of an intensified global hydrological cycle. In this study, we evaluated ORCHIDEE ET simulations with different configurations: three offline simulations with different forcing datasets and one simulation coupled to LMDz atmospheric model. The ORCHIDEE simulations were compared to the satellite-based FLUXCOM ET products. Within this evaluation, we also investigated the impact of irrigation on the biases between ORCHIDEE and the FLUXCOM ET values during the 1981 to 2010 period. While the ORCHIDEE offline simulations underestimated the FLUXCOM ET products over almost all latitudes, the ORCHIDEE simulation coupled with LMDz generally overestimated the FLUXCOM over the southern hemisphere. A structure of systematic negative bias over regions largely irrigated was found for all simulations. This deficiency in evapotranspiration seems not sensitive to the forcing datasets whether for ORCHIDEE or the FLUXCOM product over small and moderately irrigated areas except over highly irrigated areas where ORCHIDEE with GSWP3 forcing had larger bias than other offline configurations but similar to the coupled simulation. Our study highlights the importance of taking into account human activities such as irrigation in order to improve models simulation and therefore long or short-term forecasts.