Climatic elements, discharge and groundwater trends over time using Mann-Kendall Test in the Mighan Sub-basin of Arak

This study was an analytical research across 84 meteorological stations, performed in the Mighan sub-basin over a fifty-year study period (1961–2011).This research seeks to answer the basic question of how declining streamflow, increasing temperatures, and fluctuation in precipitation have impacted water resource allocation in the Mighan sub-basin. The research method is analytical based on Mann-Kendall method. Analysis of independent flow measures (discharge and groundwater levels) using the Mann-Kendall trend test suggests evidence for climate change trends for many of the 84 stations. The results highlighted a mix of positive (increasing) and negative (decreasing) trends (monthly, seasonal, and annual) in the Mighan sub-basin. The results showed that during the 10-year period (1961-70), the minimum temperature occurrence in the first decade at -33.5 ° C (1973) and the maximum temperature event in the same decade at 57 ° C (1974) made this decade one of the most volatile decades in a fifty year period. Despite the inter-annual climatic fluctuations, results revealed that the Mighan Sub-basin has encountered many severe fluctuations of precipitation and average annual discharge during the five decades.