تغيير اقليم در جنوب و جنوب غربي ايران از ديدگاه مشاهدات بارش ، بر همكنش با پديده النينيو نوسات جنوبي

Climate Change in Southern and Southwestern Iran From Precipitation Observation: Interaction with El Nino-Southern Oscillation Phenomenon

The study of climate change is pre-requisite for preparedness and mitigating the costs of such a change. In Iran, there is a little literature dealing with the identification of climate change in percipitation time series. Moreover, literature investigating the relationship between change point in climatic time series and Oceanic-Atmospheric Phenomenon was not found for Iran. The Mann-Whitney and cumulative sum tests were, therefore, conducted to reveal possible change point in percipitation (annual, biannual and seasonal) time series over southern and southwestern parts of Iran for the period 1951-1999. The results have indicated that the change point is mostly centered over the first half of the 1970s. It was shown that compared to the era before 1975, annual rainfall has increased for the period after this year for all sites studied. While rainfall in Shabankareh, Bandar Abbas and Bandar Lengeh has experienced the highest percentage of increase, the lowest increase rate has occurred in Boushehr and Shoushtar. In seasonal scale, although the percipitation has considerably increased during cold seasons (autumn and winter), the decline in spring and summer rain is a notable feature of climate change over the studied sites. In monthly scale, the highest increase rate (after 1975) was found for March. It has been found that the change point is SOI data is approximately coincided with the point in percipitation time series. The study has concluded that the recent increase in the frequency and duration of warm ENSO (El Nino Southern Oscillation) events is associated with positive trend in cold season percipitation over central south and southwestern parts of Iran.