Deficit Irrigation in a Warming World: Integrating Crop Physiology, Water Productivity and Climate-Risk Management for Sustainable Agriculture
Irrigated agriculture consumes the largest share of global freshwater withdrawals, and this dependence is intensifying as rainfall variability and evaporative demand increase under a warming climate. Deficit irrigation, defined as the deliberate application of water below full crop evapotranspiration requirements at selected growth stages, has emerged as a central strategy for reconciling food production with water scarcity. This review synthesises evidence on the physiological basis of crop responses to water deficit, the modelling frameworks used to predict yield and water productivity outcomes, and the performance of deficit irrigation across field crops, orchard and vine systems, and vegetables. The economic and behavioural dimensions of farmer adoption, the interaction between deficit irrigation and soil salinisation under changing climatic conditions, and emerging genetic and computational tools that support precision water management are also examined. Findings indicate that regulated and sustained deficit irrigation strategies can improve water productivity substantially, often between eight and thirty per cent relative to full irrigation, although yield penalties vary widely by crop, growth stage sensitivity and environmental context. Climate change is projected to alter the reliability of these gains, particularly where warming erodes the compensatory physiological mechanisms that underpin moderate water stress benefits. Economic viability depends strongly on relative water and commodity prices, and farmer adoption remains constrained by risk aversion and limited technical support. The review concludes that deficit irrigation should be understood not as a fixed prescription but as an adaptive, crop- and context-specific component of climate-risk management, requiring closer integration of physiological monitoring, crop modelling and economic decision support.