In arid and semi-arid regions, irrigation demand across crop growth stages is highly sensitive to climatic variability, posing growing challenges for water management under climate change. This study investigates the spatiotemporal dynamics and climate sensitivity of irrigation water requirements (IWR) across maize phenological stages in the West Liao River Basin (WLRB)-the agro-pastoral ecotone of northern China. Historical meteorological data (1981-2020) and future climate projections from four CMIP6 scenarios (SSP126, SSP245, SSP370, SSP585) were used to assess both past trends and scenario-based shifts in IWR. Results show a significant upward trend in IWR over the past four decades, with peak demand concentrated during the tasseling-silking and grain-filling stages. IWR sensitivity varies by hydrological year type: maximum temperature dominates under dry and wet years, while precipitation is more influential during normal years. Spatial patterns reveal a central basin hotspot of high irrigation demand. Future projections under high-emission scenarios (particularly SSP585) suggest a substantial intensification of irrigation demand, with localized increases in IWR surpassing 20% by the late 21st century. Conversely, under low-emission pathways such as SSP126, the projected increases are comparatively moderate, underscoring the critical role of climate mitigation in alleviating irrigation stress. These findings highlight the importance of stage-specific and climate-responsive irrigation planning to ensure agricultural resilience in semi-arid regions under future climate uncertainty.