Land surface models and vertical gradient estimation of evapotranspiration and other turbulent fluxes

The Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) campaign took place in Catalonia near Lleida, in the northeastern part of the Iberian Peninsula. It lasted from April to October with an intensive measurement period for the last half of July, 2021, when surface conditions between a large irrigated area and the much drier surroundings was maximum. Measurements of surface energy fluxes and atmospheric and soil conditions were made over several locations which comprised several crop types in irrigated, drip irrigated and non irrigated areas. These data were used to test the quality of the approximations made when modeling in semi-arid environments.
 
Turbulent fluxes can be estimated using two measurements at different heights of the relevant atmospheric variable with statistically-based methods like Monin-Obukhov theory or simulated from LSMs (Land Surface Models). For latent heat flux, the first approach is limited by the lack of development of the necessary functions when they are used in locations with different conditions from which they were originally developed. The second requires the determination of many parameters which depend on large scale databases or a derived land cover classification to be accurate, together with an appropriate parameterization of the physical processes. Furthermore,  evapotranspiration (ET) estimates for the LIAISE sites are affected by more complex interactions such as the heterogeneity of the region, with areas irrigated by flooding (mainly corn and alfalfa) or drip irrigation (e.g. fruit trees, vineyards) verses relatively dry rain-fed surfaces (natural grass or low vegetation, bare soil), and sudden man-induced changes such as flooding or harvest.  
    
The relationship between the lower atmospheric vertical gradients and fluxes is explored and the LSM SURFEX (Surface Externalisée in French) is evaluated with field data of LIAISE to test its ability to simulate the key processes modulating the surface fluxes (notably the impact of irrigation) over several contrasting sites.