Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye

Eray Harman; Belgin Çakmak

doi:10.15832/ankutbd.1827599

Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye

Abstract

Accurate estimation of seasonal crop water use is critical for irrigation planning in semi-arid regions. This study benchmarks net irrigation water requirement (NIWR) and crop evapotranspiration (ETc) for a Central Anatolian scheme (Eskişehir, Türkiye) over 2016–2022 using three approaches: the institutional Blaney–Criddle (General Directorate of State Hydraulic Works-DSI) baseline, Food and Agriculture Organization (FAO) CROPWAT 8.0 (Penman–Monteith, monthly climate), and SuET (Penman–Monteith, daily climate with locally tuned parameters). A drought year was additionally constructed from historically dry seasons to assess stress conditions. Across irrigated crops, DSI systematically calculates less NIWR relative to the PM-based tools: mean biases are ~130–170 mm for wheat, ~190–240 mm for potato/onion/sugar beet, ~230–250 mm for maize, ~300 mm for sunflower/melon, and ~550 mm for alfalfa, with RMSE (Root mean square error) values closely tracking these biases. CROPWAT and SuET display strong cross-method coherence—very high year-wise correlations (r ≈ 0.90–0.99) and crop wise agreement that is strong to moderate for most crops—indicating that both capture interannual climate variability consistently when parameterized with harmonized crop calendars and effective rainfall procedures. Under the drought scenario, both ETc and NIWR increase markedly for high-demand crops, underscoring elevated deficit risk if allocations rely on temperature-only norms. Overall, the findings indicate that the traditional DSI Blaney–Criddle values substantially less calculation actual crop water requirements—particularly in dry years— and that Penman–Monteith–based tools such as CROPWAT and SuET should be systematically integrated into regional irrigation planning to improve water-use efficiency and drought resilience. Where legacy DSI tables must be retained, applying crop-specific correction factors derived here can reduce allocation shortfalls and better align deliveries with climatic demand.

Keywords

Supporting Institution

Institutional support was provided by the Republic of Türkiye General Directorate of State Hydraulic Works (DSİ), 3rd Regional Directorate (Eskişehir), and Ankara University, Graduate School of Natural and Applied Sciences. The authors declare that the study received no specific funding.

Ethical Statement

The authors confirm that this research did not involve experiments on humans or animals and did not require ethics committee approval. The study relies on institutional irrigation planning records and publicly available/official meteorological datasets. All data were used in compliance with institutional and national regulations. The authors declare that there is no conflict of interest to disclose. This article is derived from the doctoral dissertation of Eray Harman at Ankara University, Graduate School of Natural and Applied Sciences.

Thanks

The authors gratefully acknowledge the Republic of Türkiye State Hydraulic Works (DSİ), 3rd Regional Directorate (Eskişehir) for institutional support and access to planning records, and Ankara University, Graduate School of Natural and Applied Sciences for academic guidance during the doctoral study. This publication is derived from the doctoral dissertation of Eray Harman under superviser Prof. Belgin Çakmak conducted at Ankara University.

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Details

Primary Language

English

Subjects

Agricultural Water Management

Journal Section

Research Article

Authors

Eray Harman ^*
0009-0007-4114-2928
Türkiye

Belgin Çakmak
0000-0003-3557-8411
Türkiye

Publication Date

July 28, 2026

Submission Date

November 20, 2025

Acceptance Date

March 3, 2026

Published in Issue

Year 2026 Volume: 32 Number: 3

DOI

https://doi.org/10.15832/ankutbd.1827599

IZ

https://izlik.org/JA85LP95MU

Cite

RIS / Bibtex

APA

Harman, E., & Çakmak, B. (2026). Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye. Journal of Agricultural Sciences, 32(3), 776-792. https://doi.org/10.15832/ankutbd.1827599

AMA

1.Harman E, Çakmak B. Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye. J Agr Sci-Tarim Bili. 2026;32(3):776-792. doi:10.15832/ankutbd.1827599

Chicago

Harman, Eray, and Belgin Çakmak. 2026. “Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye”. Journal of Agricultural Sciences 32 (3): 776-92. https://doi.org/10.15832/ankutbd.1827599.

EndNote

Harman E, Çakmak B (July 1, 2026) Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye. Journal of Agricultural Sciences 32 3 776–792.

IEEE

[1]E. Harman and B. Çakmak, “Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye”, J Agr Sci-Tarim Bili, vol. 32, no. 3, pp. 776–792, July 2026, doi: 10.15832/ankutbd.1827599.

ISNAD

Harman, Eray - Çakmak, Belgin. “Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye”. Journal of Agricultural Sciences 32/3 (July 1, 2026): 776-792. https://doi.org/10.15832/ankutbd.1827599.

JAMA

1.Harman E, Çakmak B. Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye. J Agr Sci-Tarim Bili. 2026;32:776–792.

MLA

Harman, Eray, and Belgin Çakmak. “Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye”. Journal of Agricultural Sciences, vol. 32, no. 3, July 2026, pp. 776-92, doi:10.15832/ankutbd.1827599.

Vancouver

1.Eray Harman, Belgin Çakmak. Comparison of Crop Irrigation Water Requirement Estimation Methods under Drought Conditions in a Semi-Arid Region of Türkiye. J Agr Sci-Tarim Bili. 2026 Jul. 1;32(3):776-92. doi:10.15832/ankutbd.1827599