Document Type : Research Paper
Authors
1 Department of Forestry and Forest Economics, Faculty of 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, Kashan, Iran
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 (ZMK = 4.54) and Khorramabad (ZMK = 4.25). The mean maximum annual CDD was 142 days (maximum: 202) in Kermanshah and 145 days (maximum: 195) in Khorramabad. Across the before and after decline, no significant trend was identified for mean maximum annual CDD trend. Despite a slight increase in CDD in Kermanshah (141→144) and Khorramabad (144→146), the annual series showed no significant trend over before and after decline. The degradation of the Zagros Forests cannot be attributed solely to declining rainfall, as concurrent changes in other climatic factors have also contributed to accelerating this decline.
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