The Impact of Climate Change on Crop Water Requirements Using Climate Models in Moghan Irrigation Network

Document Type : Research Paper

Authors

Department of Water Engineering and Management, Faculty of Agriculture, the University of Tarbiat Modares, Tehran, Iran.

10.22059/jwim.2025.393855.1222

Abstract

The impact of climate change on crop water requirement and irrigation water demand is crucial for evaluating agricultural productivity especially in semi-arid regions. This study investigates crop water requirement (CWR) and irrigation water requirement (IWR) in Moghan irrigation network, focusing on forecasting future irrigation water demands. Daily temperature and precipitation data from climate models under three scenarios (optimistic, intermediate, and pessimistic) were downscaled. Model results indicate that in the future, maximum temperature will increase by 0.68 to 2.05 °C, minimum temperature by 1.21 to 3.12 °C, and annual precipitation will change between -21.06% and +27.14%. These changes will increase seasonal climate variability and instability in the region. Crop water requirements and net irrigation needs will rise in all seasons. Uncertainty in model estimates for seasonal changes in crop water requirement and net irrigation demand is lower in summer and autumn compared to spring and winter. This study estimated water requirements for main crops in the Moghan network—including wheat, alfalfa, peanut, cotton, and vegetables—using the FAO 56 method. Results show that irrigation water needs and total water demand will increase by 12.77% to 13.76%. The irrigation adequacy index in the Moghan network for the 2025–2044 period will be decreased by 15%, and is far below one, indicating that the volume of water delivered to farms will be insufficient to meet estimated net irrigation demand. This shortage is driven by increased water demand due to higher temperatures and evapotranspiration, and reduced effective rainfall. Consequently, water stress, reduced crop yields, and increased vulnerability of farmers are expected. This situation highlights the need to revise water allocation, modify cropping patterns, and improve irrigation network efficiency for sustainable agricultural water management.

Subsequently, the water requirements of crops such as wheat (46%, 26848 hectares), alfalfa (15%, 8539 hectares), cotton (6%, 3468 hectares), peanuts (5%, 2915 hectares), other cereals (15%, 8771 hectares), vegetables (12%, 7116 hectares), and legumes (1%, 645 hectares) were calculated. Initially, using the method recommended by FAO 56 for calculating reference crop evapotranspiration in the absence of data, reference evapotranspiration was calculated based on the mentioned models and scenarios. Finally, considering the effective daily precipitation, the crop water requirements were estimated.

Assuming no change in the cropping pattern, and cultivated area of the irrigation network, the net irrigation water requirement of the network was calculated. The results show that under the mentioned scenarios for the period 2025-2044, the average water requirement, and water demand volume of the network, will increase by 3.05%-6.72% and 13.85%-20.69% per year, respectively. The irrigation adequacy index in the Moghan network for the 2025–2044 period will be decreased by 15%, and is far below one, indicating that the volume of water delivered to farms will be insufficient to meet estimated net irrigation demand. This shortage is driven by increased water demand due to higher temperatures and evapotranspiration, and reduced effective rainfall. Consequently, water stress, reduced crop yields, and increased vulnerability of farmers are expected. This situation highlights the need to revise water allocation, modify cropping patterns, and improve irrigation network efficiency for sustainable agricultural water management.

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References

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Water and Irrigation Management
Volume 15, Issue 2
October 2025
Pages 355-377

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