Are precipitation characteristics and patterns impacting oak trees decline in the Zagros region of western Iran?

The objective was to investigate if changes in annual, monthly, and seasonal precipitation are associated with emergence of declining oak trees in Iran. Daily precipitation data were obtained from ۲۰ synoptic stations distributed over the Zagros area from ۱۹۸۸-۲۰۱۹. Non-parametric Mann-Kendall (MK) test and Sen's Slope estimator (Qmed value) were applied to identify significant trends in the precipitation data. ‘‘De Martonne’’ climate classification (i.e., De Martonne aridity index (IDM) was used for climate classification. Although most stations showed decreasing trends in annual precipitation during the studied period (۱۹۸۸-۲۰۱۹), these trends were statistically significant at only two stations. The mean number of events per year pre- and post- oak decline was not significantly different (۶۸ events before against ۷۱ events after decline). Most of the annual precipitation in the Zagros region falls in winter and spring (۸۰% in total). However, this ratio decreased after the year ۲۰۰۰ by ۶% (not significant) compared with before. The difference between the average annual precipitation, before (۱۹۸۸-۲۰۰۰) and after (۲۰۰۰-۲۰۱۹) the emergence of the oak decline phenomenon, were not statistically significant in any of the climate types (semi-arid: ۴۰۶ mm vs. ۳۷۸ mm), Mediterranean (۵۳۰ mm vs. ۴۸۹ mm), and humid (۹۲۴ mm vs. ۹۱۲ mm) as well as in whole Zagros region (۵۳۷ mm vs. ۵۰۸ mm). Although our data suggested insignificant trends in precipitation for most stations, future research should investigate if rising temperature in the Zagros area has resulted in higher evaporation and drier soil thereby accelerating the oak tree decline.

کلیدواژه ها:

Climate Change ، Mann–Kendall test ، Quercus brantii