Recent advances in hydrological modeling have quantified unsustainable irrigation water consumption (UIWC), underscoring its impacts on freshwater stocks depletion and environmental flows impairment. However, the long-term sustainability of irrigation under different climate change scenarios remains insufficiently explored. Here, we assess future trajectories of UIWC using an ensemble of simulations under a sustainable development pathway (SSP1-2.6) and a high-emissions pathway (SSP5-8.5), projecting changes through each decade until 2100. The baseline estimate of global UIWC is 458 km3 yr−1. Global UIWC is projected to increase under climate change, but multi-model projections show substantial uncertainty. By 2100, estimates range from 458 to 546 km3 yr−1 under the low-emission SSP1-2.6 scenario, and from 456 to 638 km3 yr−1 under the high-emission SSP5-8.5 scenario, highlighting divergent future outcomes depending on emissions pathways and model assumptions. Under baseline conditions, the Ganges, Sabarmati, and Indus basins have the highest UIWC. Climate change scenarios show divergent regional trends, with the SSP5-8.5 scenario projecting larger increases in UIWC—especially in the Ganges, Indus, and US High Plains—compared to SSP1-2.6. These increases reflect both greater climate impacts and higher model uncertainty. Normalizing UIWC by irrigated area reveals hotspots of irrigation pressure, particularly in South Asia and the Nile Delta, where per-area UIWC exceeds 50 mm yr−1, and is projected to rise further under both scenarios. By assessing multi-model water scarcity risks in irrigated croplands, these findings provide crucial insights for guiding climate change adaptation strategies in agriculture.

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