Statistical Study of Dry and Wet Years in the Middle-West of Iran

One of the main characteristics of the Earth's system is climate change on short and long time-scales which imposes fluctuations in climatic parameters such as temperature and precipitation. These fluctuations are severe in some parts of the world and cause disturbances in natural ecosystems.
Drought is a climate fluctuation that affects many of the arid and semi-arid regions of the world with different intensity. The mountainous region of the west of Iran has severe precipitation fluctuations due to having a semi-arid to semi-humid climate regime, which causes increasing damage in years of drought.
In this research, air temperature and rainfall variations in the Middle-west region of Iran were determined using statistical methods and data from synoptic stations in Arak, Ilam, Khorramabad, Zanjan, Sanandaj, Kermanshah and Hamedan, and the frequency of dry and wet years and the statistical relationship between the two phenomena were studied and evaluated.
Statistical calculations were made on the monthly and annual rainfall and temperature data of the studied stations. Moreover, according to the results, it seems that on average a four-year fluctuation is predominant in the precipitation regime of the region, and the trend of precipitation changes indicate regular fluctuations in dry and wet years.