Irrigation strongly influences near-surface conditions and induces breeze circulation: Observational and model-based evidence

Irrigation is becoming increasingly common in agriculture and is essential to meet the growing demand for food. Studies of the impact of irrigated areas on local meteorology reveal a strong influence on near-surface conditions, although the extent of this influence varies considerably between locations. In addition, though theoretical evidence suggests that irrigation can create breeze-like atmospheric boundary-layer circulations, observational evidence is still lacking. This study investigates the effects of irrigation on the surface and atmospheric boundary layer in the Ebro basin, an intensively irrigated area with a semi-arid climate in northeastern Spain. Observational data from the international field campaign Land Surface Interactions with the Atmosphere over the Iberian Semi-arid Environment are analysed together with coupled surface-atmosphere model output to better understand and quantify the impact of irrigation on the lower atmosphere. A simple parametrization of irrigation is shown to improve the accuracy of the model. Results demonstrate that irrigation increases the average latent heat flux by over 200 W<middle dot>$$ \cdotp $$m -2$$ {}<^>{-2} $$, reduces air temperature by 4.7 degrees C, and increases specific humidity by 50% at 2 m during the day over the irrigated region of the domain. Moreover, irrigation limits convection and strongly stabilizes the atmospheric boundary layer. Notably, the study provides evidence for an irrigation-induced breeze from the irrigated area to the semi-arid area. These findings highlight the importance of considering irrigation in numerical models for weather forecasting, climate modelling and sustainable agricultural planning. Thanks to the combined use of mesoscale simulations and observations, the impact of irrigation on the atmospheric boundary layer in northeastern Spain is quantified. It is shown that irrigation reduces air temperature and increases specific humidity at 2 m during the day over the irrigated region of the area. It also limits convection, stabilizes the atmospheric boundary layer, and induces a breeze from the irrigated area to the semi-arid area. image