Hakami-Kermani et al. (2025) Evapotranspiration and water requirement changes of main crops under climate change conditions in a semi-arid region

Identification

• Journal: Applied Water Science
• Year: 2025
• Date: 2025-11-27
• Authors: Avin Hakami-Kermani, Hossein Babazadeh
• DOI: 10.1007/s13201-025-02696-8

Research Groups

• Department of Water Science and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Short Summary

This study projects future changes in evapotranspiration and water requirements for major crops (barley, wheat, alfalfa, cotton) in Iran's semi-arid Garmsar Plain under various climate change scenarios (2025-2100), finding a general increase in temperatures, reference evapotranspiration, and crop water demands, particularly for alfalfa and cotton.

Objective

• To assess the changes in evapotranspiration for key crops (barley, wheat, alfalfa, and cotton) in the Garmsar Plain due to uncertainties in climate model outputs during the period 2025–2100. This involves analyzing climate change impacts on temperature and precipitation variables through statistical downscaling of GCM outputs under different Shared Socioeconomic Pathways (SSPs) and quantifying the uncertainty in future evapotranspiration estimates.

Study Configuration

• Spatial Scale: Garmsar Plain, western part of Iran (37,570 hectares, 51° 53’ to 52° 55’ E longitude and 34° 28’ to 35° 30’ N latitude).
• Temporal Scale:
  • Baseline: 1986–2014
  • Future periods: 2025–2100, divided into 2025–2050, 2051–2075, and 2076–2100.

Methodology and Data

• Models used:
  • Global Circulation Models (GCMs): CanESM5, MPI-ESM1-2-HR, NorESM2-MM (from CMIP6).
  • Downscaling Model: Statistical Downscaling Model (SDSM) version 6.1.
  • Reference Evapotranspiration (ETo) Model: Hargreaves–Samani (H-S) method.
  • Crop Evapotranspiration (ETc): FAO56 crop coefficient (Kc) method.
  • Effective Precipitation (Peff): Soil Conservation Service (SCS) method.
• Data sources:
  • Local climatic variables: Daily precipitation, minimum, maximum, and mean temperatures from Garmsar synoptic station (1986–2014).
  • Predictor variables for SDSM: 26 atmospheric variables from the National Centers for Environmental Prediction (NCEP) dataset.
  • GCM outputs: CMIP6 under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5).

Main Results

• Both maximum and minimum temperatures are projected to increase consistently across all scenarios and periods, with the highest rises in autumn and minimal changes in winter.
• Precipitation shows a generally increasing trend in most months, but with significant seasonal and monthly variability. Spring and summer are projected to have the highest relative precipitation increases, while autumn is expected to experience the most significant declines.
• Reference evapotranspiration (ETo) shows an overall increasing trend across all scenarios and periods, with greater increases in later periods (2076-2100). The most pronounced increases are in autumn and summer, and the least in winter. Annual ETo increases range from 5.12% (2025-2050, SSP3-7.0) to 6.4% (2076-2100, SSP5-8.5).
• Crop water requirements (ETc) for barley, wheat, alfalfa, and cotton are projected to increase. Alfalfa and cotton show the most significant increases in water use (7.7-8.61% and 7.05-9.28% respectively) due to their longer growing seasons, while wheat shows the lowest increase.
• The average range of variation in ETo uncertainty decreases by 64.7% compared to the baseline, indicating increased certainty in future ETo projections due to rising temperatures.
• The projected increases in temperature and ETo, coupled with decreased autumn precipitation, will lead to increased irrigation demands and significant water stress in the Garmsar Plain, particularly towards the end of the century.

Contributions

• Provides a comprehensive assessment of climate change impacts on reference evapotranspiration and crop water requirements in the semi-arid Garmsar Plain, Iran.
• Incorporates uncertainty analysis from multiple CMIP6 GCMs and SSP scenarios across three distinct future periods (2025-2100) for local-scale projections.
• Quantifies specific changes in water requirements for key regional crops (barley, wheat, alfalfa, cotton), highlighting those most vulnerable to increased water demand.
• Emphasizes the critical need for adaptive agricultural planning, optimized cropping patterns, and efficient water resource management strategies in semi-arid regions facing climate change impacts.

Funding

• The authors received no financial support for the research, authorship, and/or publication of this article.

Citation

@article{HakamiKermani2025Evapotranspiration,
  author = {Hakami-Kermani, Avin and Babazadeh, Hossein},
  title = {Evapotranspiration and water requirement changes of main crops under climate change conditions in a semi-arid region},
  journal = {Applied Water Science},
  year = {2025},
  doi = {10.1007/s13201-025-02696-8},
  url = {https://doi.org/10.1007/s13201-025-02696-8}
}