From Present-Day Validation to Future Projections: AR6 SSP Scenario Assessment of Water Availability, Irrigation Demand, and Paddy Rice Yield in the Zhuoshui River Basin Using a Water–Crop Model

In recent decades, climate change has intensified hydrometeorological extremes and altered seasonal water availability, posing growing challenges to irrigated agriculture in subtropical river basins. Taiwan has experienced a sustained warming trend over the past century, and projected changes in precipitation seasonality under IPCC AR6 scenarios may further amplify uncertainty in irrigation supply and rice production.

This study develops and validates a basin-specific Water–Crop modeling framework for the first rice cropping season in the Zhuoshui River Basin, Taiwan. Historical meteorological data (precipitation and temperature) and hydrological observations (river discharge as a proxy for water availability) are integrated to quantify the coupled dynamics of water availability, irrigation demand, and paddy rice yield. The crop-yield component is implemented using a long short-term memory (LSTM) model to capture nonlinear responses, lag effects, and interactions among hydroclimatic drivers, while the water module represents basin-scale constraints that regulate irrigation supply.

Based on the validated model outputs, we further derive a basin-specific drought–yield indicator that uses yield anomalies as an integrated measure of agricultural drought impacts, complementing conventional indices based solely on precipitation or streamflow. Finally, AR6 climate projections (SSP2-4.5 and SSP5-8.5) are used to force the modeling framework to assess future changes in water availability, irrigation demand, drought–yield risk, and yield outcomes under contrasting socio-economic pathways.

The proposed framework provides a physically and data-informed tool for diagnosing how climate-driven shifts in basin hydrology translate into irrigation constraints and rice yield risks. The results support decision-making for irrigation allocation, drought preparedness, fallow planning, and adaptation strategies in the Zhuoshui River Basin.