Investigation of the trend of hydroclimatology changes using non-parametric tests in the Kasilian watershed of Mazandaran Province

Significant reductions in runoff have created severe challenges and complexities in water resources development projects. Protecting the rights of stakeholders and investments in dams and other water facilities requires recognizing hydro climatological changes. This study aimed to investigate the changes in precipitation and temperature on the 60-year discharge trend of the Kasilian watershed by non-parametric Mann-Kendall and Sen's Slope tests. In these studies, the discharge of Kasilian station, rainfall and temperature of 16 stations have been analyzed. Using non-parametric Mann-Kendall and Sen's Slope tests, the increasing or decreasing trend was tested monthly, seasonally, and annually at 5%. The results show that the annual discharge has a significant negative trend. Also, all seasons are faced with a decrease in discharge, the trend of which is significant in spring, summer, and autumn. However, the precipitation of the Kasilian basin does not have a significant trend at the level of 5%. The average maximum temperature in three months of the year also the average annual maximum have a significant positive trend. The average minimum temperature of the basin in all months of the year has a significant upward trend. The highest temperature increase is also observed in autumn. One of the most important reasons for the decrease in discharge, despite being almost safe from development factors and upstream compared to most of the country's watersheds, is the increase in the average minimum temperature, which is one of the essential factors in reducing discharge in this area.