Climate change is altering crop water demand and production efficiency, yet its impacts on irrigation water requirements (IWR) and crop water productivity (WP_c) remain insufficiently understood at the regional scale. Here, we quantified long-term climate impacts on irrigated maize and wheat systems across the Yellow River Basin (YRB) during 1975–2024, with a coupled agro-hydrological model (EPIC-SWBM). Climate-driven changes were attributed to shifts in three pathways, including atmospheric water supply, evaporative demand, and temperature-related crop response, using Shapley value analysis. IWR showed increasing trends across all maize sub-regions with no statistically significant trends detected, while maize WP_c declined significantly in the central, southern, and southeastern basin by up to 0.03 kg m⁻³ decade⁻¹. Wheat WP_c also declined in parts of the western and central basin, whereas wheat IWR increased significantly in the western and north-central basin, at rates of 9.4 and 11.8 mm decade⁻¹, respectively. Rising evaporative demand was the dominant driver of increasing irrigation pressure and declining WP_c in most regions, whereas precipitation increases partly offset irrigation pressure in wetter areas, especially in the southeastern basin. Based on the combined trends of IWR and WP_c, 32.9% of maize-growing areas and 33.3% of wheat-growing areas were classified as high risk. These findings highlight the growing imbalance between water demand and production efficiency under climate change and underscore the need for pathway-specific adaptation, including soil moisture conservation in demand-driven regions and crop adaptation where thermal stress becomes a key constraint.