Assessment of Crop Water Requirements and Irrigation Scheduling under Climate Change Scenarios using the FAO-CROPWAT Model: A Review

Abstract

Efficient agricultural water management is increasingly important under conditions of climate variability, climate change and growing sectoral competition for water resources. This review synthesizes 22 peer-reviewed studies published between 1994 and 2024 that applied the FAO–CROPWAT model to estimate evapotranspiration, seasonal crop water demand and irrigation planning across diverse agro-climatic regions. Studies were selected based on the application of the FAO Penman–Monteith method for reference evapotranspiration estimation and systematic assessment of field- and command-area–scale water requirements, including climate change scenarios. The reviewed literature demonstrates substantial regional variability in seasonal water demand influenced by crop type, growth stage, climatic conditions, soil properties and irrigation efficiency. A consistent stage-wise pattern was observed across crops, with minimum demand during the initial stage, increasing through development, peaking at mid-season and declining toward maturity. Effective rainfall significantly reduced irrigation dependence in humid regions, whereas semi-arid areas exhibited greater reliance on supplemental irrigation due to high evaporative demand. Climate projections consistently indicate rising evapotranspiration and increased future irrigation requirements under warming scenarios and altered precipitation regimes. Overall, the FAO–CROPWAT model is confirmed as a reliable decision-support tool for irrigation scheduling and climate-resilient water management, supporting sustainable agricultural production and long-term food security.