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Abstract This paper analyzed observations from the Great Plains Irrigation Experiment (GRAINEX) to better understand L-A interactions and PBL evolution. This study is focused on a day when the largest forcing on the boundary layer originated from the land surface/land use. To examine these impacts, we also applied the Weather Research and Forecasting (WRF) model. Results from the observations show that compared to non-irrigated areas, air temperature, wind speed, and PBL height were lower while dew point temperature and latent heat flux were higher over irrigated areas. Findings suggest that entrainment layer drying and differences in energy partitioning over irrigated and non-irrigated areas played an important role in PBL evolution. In the final hours of the day, the PBL collapsed faster over non-irrigated areas compared to irrigated. The WRF model simulations agree with these observations. They also show that the extent of irrigation (expressed as irrigation fraction or IF) in an area impacts L-A response. Under ∼60% IF, the latent heat flux and mixing ratio reach their highest value while temperature and PBLH are at their lowest, and sensible heat flux is near its lowest value. Results are reversed for ∼2% IF. It is concluded that irrigation notably impacts L-A interactions and PBL evolution.