Pary et al. (2026) Trends of rainfed and irrigated crop yield influenced more by increased cultivated area than drought in Iran

Identification

• Journal: Regional Environmental Change
• Year: 2026
• Date: 2026-02-16
• Authors: Atefeh Torkaman Pary, Pejvak Rastgoo, Dirk Zeuss, Temesgen Alemayehu Abera
• DOI: 10.1007/s10113-025-02499-2

Research Groups

• Department of Environmental Informatics, Faculty of Geography, Philipps-Universität Marburg, Germany.
• Earth Change Observation Laboratory, Department of Geosciences and Geography, University of Helsinki, Finland.

Short Summary

This study quantifies the drivers of wheat and barley yield trends in Iran from 1995 to 2022, revealing that the expansion of cultivated area had a significantly larger influence (71–87%) on total production than drought (12–29%). While irrigation provided a buffer, rainfed systems—particularly wheat—remained highly vulnerable to climatic stressors.

Objective

• To evaluate the spatio-temporal impacts of drought severity and changes in cultivated area on wheat and barley yields in both rainfed and irrigated agricultural systems across Iran over a 27-year period.

Study Configuration

• Spatial Scale: National level (Iran), encompassing 31 provinces across diverse arid and semi-arid climatic zones.
• Temporal Scale: 1995–2022 (Annual agricultural data; monthly drought indices).

Methodology and Data

• Models used: Non-parametric Mann–Kendall (MK) trend test, Theil–Sen slope estimator, linear regression, and non-linear Boosted Regression Tree (BRT) models.
• Data sources:
  • Annual crop yields and cultivated area data from the Ministry of Agriculture Jahad of Iran.
  • 12-month Standardized Precipitation Evapotranspiration Index (SPEI) derived from a global high-resolution (5 km) dataset (CEDA/NERC), utilizing CHIRPS v2, MSWEP v2.8, and GLEAM v3.7a.
  • Topographic data from the USGS 30 m Digital Elevation Model.

Main Results

• Yield Trends: Overall crop yields increased by 0.26 $t/ha/yr$ in irrigated systems and 0.075 $t/ha/yr$ in rainfed systems.
• Area Expansion: Total cultivated area increased by up to 40% in irrigated systems and 38% in rainfed systems.
• Relative Contribution: Cultivated area expansion was the dominant driver of yield trends, explaining 71% to 87% of variability, whereas drought explained only 12% to 29%.
• Drought Impact: Drought severity accounted for yield reductions of 12–29% across systems. Rainfed wheat was the most sensitive, with drought explaining up to 34% of yield anomalies in specific provinces.
• System Resilience: Irrigated systems showed higher stability but faced declining yields in central and southern provinces due to groundwater depletion and soil salinity.

Contributions

• Provides the first nationwide comparative assessment of both rainfed and irrigated systems across Iran’s diverse climatic zones.
• Quantifies the "masking effect" of land expansion, showing that policy-driven increases in cultivated area have historically buffered the national food supply against the negative impacts of intensifying droughts.
• Highlights the critical threshold where area expansion can no longer compensate for climatic stressors, emphasizing the need for sustainable intensification over land expansion.

Funding

• Publication fund from the Philipps-Universität Marburg.
• Open Access funding enabled and organized by Projekt DEAL.

Citation

@article{Pary2026Trends,
  author = {Pary, Atefeh Torkaman and Rastgoo, Pejvak and Zeuss, Dirk and Abera, Temesgen Alemayehu},
  title = {Trends of rainfed and irrigated crop yield influenced more by increased cultivated area than drought in Iran},
  journal = {Regional Environmental Change},
  year = {2026},
  doi = {10.1007/s10113-025-02499-2},
  url = {https://doi.org/10.1007/s10113-025-02499-2}
}

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