Long-term trends in consecutive dry days and the decline of Zagros Forests in Kermanshah and Khorramabad Provinces

Mirzaei, Somayeh; Attarod, Pedram; Pourhashemi, Mehdi; Arghavani, Abbas; Beiranvand, Samira

doi:10.22059/jrwm.2026.407983.1860

Document Type : Research Paper

Authors

¹ Department of Forestry and Forest Economics, Faculty of Natural Resources, University College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

² Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

³ Kashan Meteorological Bureau, Esfahan, Iran

10.22059/jrwm.2026.407983.1860

Abstract

The aim of the study was to evaluate long-term trends in precipitation and consecutive dry days (CDD), and their association with the decline in Zagros forests. Daily meteorological data were obtained from Kermanshah and Khorramabad synoptic weather stations and analyzed for a 49-year period (1975-2023). The Mann-Kendall (MK) test was used to assess the trends in precipitation and CDD, and the t-test was applied to compare the mean values. For this purpose, precipitation values less than 0.1 mm for rainy days and less than 1 mm for dry days were excluded, respectively. The mean annual precipitation (±SD) was 418±104 in Kermanshah and 485±130 in Khorramabad, and no significant trend was detected. Before the decline, mean annual precipitation was 438 ± 107 mm and 501 ± 121 mm in Kermanshah and Khorramabad, respectively. In the period after the decline, annual precipitation reduced to 390±95 mm in Kermanshah and 465±143 mm in Khorramabad, with no significant trend detected. The mean annual number of dry days exhibited a significant increasing trend in both Kermanshah (Z_MK = 4.54) and Khorramabad (Z_MK = 4.25). The mean maximum annual CDD was 142 days (maximum: 202) in Kermanshah and 145 days (maximum: 195) in Khorramabad. We detected statistically significant increasing trends in the mean annual CDD at both stations (Z_MK=4.15 in Kermanshah and 3.04 in Khorramabad). Annual precipitation changes are not the main driver of oak decline in the Zagros. Longer and more constant dry periods, reflected in the CDD index, along with rising temperatures, have increased water stress and reduced forest resilience.

Keywords

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Journal of Range and Watershed Managment

Long-term trends in consecutive dry days and the decline of Zagros Forests in Kermanshah and Khorramabad Provinces

References

References

Volume 79, Issue 2
July 2026
Pages 205-220

Long-term trends in consecutive dry days and the decline of Zagros Forests in Kermanshah and Khorramabad Provinces

References

References

Volume 79, Issue 2July 2026Pages 205-220

Volume 79, Issue 2
July 2026
Pages 205-220