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Dams are studied not only for the benefits of construction but also for their environmental impacts. Providing drinking and agricultural water, flood control and power plant construction are some benefits of dams. Due to large evaporation area behind dams, their environmental impacts on local climatic parameters or regional ecosystem, affects the benefits of their construction. In this study, the most important methods of non-parametric statistical analysis, including common Mann-Kendall test and the Sen's slope estimator due to their appropriateness for the time series of meteorological observational data were used. The effects of the Gotvand Dam construction on three climatic parameters i.e. humidity, temperature and precipitation, have been investigated and evaluated by using data from five meteorological stations in the Dam area from 2001 to 2017, by time-series trend analysis on monthly and annual scales using non-parametric method of Sen's slope estimator and Mann- Kendall test. Evaluating the data of three stations near the Dam location and comparing them with the data of two control stations away from the Dam, showed that after Dam impoundment i.e. in August 2011, relative humidity and average temperature factors have increased and the annual precipitation has decreased in the area. A combination of significant increasing and decreasing trends at 95% confidence level was observed at various stations. In July, the average monthly temperature showed an increasing trend in Masjed Soleiman and Shushtar stations, but in other months or during the annual period at the stations under study, at a 95% confidence level, a significant trend for the average temperature was not observed. The average relative humidity trend analysis showed that Dezful Airport (in September and November), Shushtar station (in September) and Lali station (in June) had a significant increasing trend and Gotvand station (in July) showed a significant decreasing trend at a 95% confidence level. However, in other months or during the annual period at the stations under study, at this level of confidence, there was no significant trend for relative humidity. Only Dezful Airport station showed a significant decreasing trend at 95% confidence level for total rainfall on annual scale. In other months or during the annual period in other stations, no significant trend was recorded for total rainfall at 95% confidence level. Further studies are needed to determine exactly whether these changes are absolutely due to the Dam or caused by global climate change contributes. [ABSTRACT FROM AUTHOR]