Climate impacts on agricultural water use revealed by multi-cropping irrigation dynamics in the Poyang Lake basin

Future climate change is expected to modify the magnitude and timing of agricultural irrigation demand, but the mechanisms remain uncertain in humid monsoon regions where increased precipitation may offset warming-induced evapotranspiration. This study assesses future irrigation water use (IWU) over the Poyang Lake basin, China, using a previously developed NOAH-HMS land surface–hydrological model coupled with a crop-specific irrigation (CDI) scheme that distinguishes paddy rice and non-rice crops. Simulations are driven by bias-corrected CORDEX–East Asia climate projections under RCP2.6 and RCP8.5 for the mid-century (2031–2060) and late-century (2065–2094) periods. Results show that basin-mean IWU decreases in most future scenarios by about 3%–9%, mainly because projected precipitation increases largely offset warming-enhanced evapotranspiration. However, this basin-scale decline conceals seasonal and spatial heterogeneity. Regional IWU exhibits a “summer decline–autumn increase” pattern, with reductions in July–August and increases in October–November. Although rice IWU decreases, its within-season rise during the growing period becomes steeper. Non-rice IWU remains concentrated in late autumn and shows stronger sensitivity to warming and drying. Precipitation–temperature quadrant analysis shows that IWU in Dry–Hot years is generally higher than in wetter states, with the strongest increase occurring in the mid-century. Precipitation remains the primary driver of interannual IWU variability, but temperature exerts increasing influence toward the late century. These results demonstrate that basin-mean IWU changes alone could underestimate future irrigation risks, emphasizing the need to consider seasonal redistribution, crop-specific responses, local hotspots, and compound extremes in agricultural water management.