Sensitivity analysis of rainfed wheat yield to climatic indices using the interpretable XGBoost–SHAP model under climate change conditions: Zanjan Province case study

Articles in Press

Document Type : Research Paper

Authors

1 irrigation and reclamation engineering, agricultural and forest meteorology, University of tehran

2 Associate Prof., Irrigation & Reclamation Engrg. Dept. University of Tehran Karaj, Iran.

Abstract

This study aimed to assess the sensitivity of rainfed wheat yield to climatic indices over the period 1990–2023 across three representative stations in Zanjan Province, Iran —Zanjan, Khodabandeh, and Khorramdarreh. The Extreme Gradient Boosting (XGBoost) algorithm, interpreted via SHapley Additive exPlanations (SHAP) values, was employed to identify the most influential climatic variables and to determine their optimal and yield-limiting thresholds. The methodological framework integrated four key approaches that have been seldom considered simultaneously in previous research: (i) estimating the length of the growing period (LGP) based on updated FAO guidelines, (ii) aligning climatic data with the actual crop growing period, (iii) focusing on the temporal distribution patterns of climatic indices rather than solely on their cumulative or seasonal means, and (iv) performing interactive and interpretable climatic analysis. The results indicated increasing trends in both yield and LGP across all three sites, although the LGP trend in Zanjan was statistically non-significant (P > 0.1). SHAP analysis revealed that moisture-related variables were the primary determinants of yield in all sites. Specifically, effective rainfall (ERGP: 1.8–2.9 mm/day) in Khodabandeh, the number of precipitation days (N_pr^GP: 4–31 days) in Zanjan, and uniform rainfall distribution (URGP: 11.2–31 mm) in Khorramdarreh emerged as the most influential positive drivers. Conversely, yield limitations were associated with shortened growing periods (LGP: 50–68 days) in Khodabandeh, poorly distributed rainfall (UR/ER: 5.4–10 mm) in Khorramdarreh, and a low number of precipitation days in Zanjan.

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Iranian Journal of Soil and Water Research

Articles in Press, Accepted Manuscript
Available Online from 07 February 2026

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