Influence of irrigation on land-surface interactions and the atmospheric boundary layer in a semi-arid region – Results from the LIAISE campaign

Irrigation is still widely neglected in land surface models which are used for numerical weather prediction. However, with the general improvement of coupled surface-atmosphere models and the evolution towards kilometer or hectometer grids, this omission is beginning to be reconsidered. Better understanding the links between the strong surface heterogeneity and local meteorology is one of the objectives of the LIAISE (Land surface Interactions with the Atmosphere In Semi-Arid Environment) project. The work presented here focuses on two clear and warm days of the special observation period of the LIAISE campaign that took place during the summer of 2021 in northeastern Spain. The coupled surface-atmosphere model Surfex-MesoNH is used to model two days of interest with and without an irrigation parameterization. The model outputs are then compared to multiple surface-based and airborne observational data. A clear improvement is provided by the irrigation representation. In particular, the modeled sensible and latent heat fluxes are reconciled with the observations, the temperature biases at 2m are corrected up to 5°C, and the specific humidity is increased by about 50% around noon near the surface. It is also shown that irrigation leads to changes in the structure and height of the atmospheric boundary layer. A breeze-like, non-classical mesoscale circulation induced by the surface contrasts between the irrigated area and the surrounding semi-arid area is highlighted.