Although all the reasons of climate changes or no changes are unknown, discussing about climate changes has always been the center of researchers' attention. The objective of this research is trend analysis of temperature and rainfall parameters in 35 synoptic stations of Iran . In this study time series of rainfall consist of: Number of rainy days, number of rainy days with equal to or greater than 1 mm, number of rainy days with equal to or greater than 10 mm, greater daily of precipitation, monthly and yearly rainfall, and time series of temperature consist of: Average of maximum temperature, average of minimum temperature, absolute maximum temperature and absolute minimum temperature. In addition relative humidity in 3, 9 and 15 utc and fastest wind speed per annum and monthly for 35 synoptic stations were analyzed to assess climate variability in Iran . In this study for determination of trend the parametric and non-parametric tests were used (Mann-Kendall, Mann-Whitney (non-parametric) and t-test (parametric)). The results of monthly rainfall trends by Mann-Kendall test showed that most of synoptic stations have no significant trends in spring, summer, autumn and winter. Analyzing the annual rainfall trends also showed that there are no significant trends in more than 80% of synoptic stations. Analyzing the number of rainy days by Mann-Kendall test showed that most of the areas in Iran have no significant trends in March but nearly half of Iran has significant negative trends in April. Almost all of the synoptic stations have no significant trends in summer, autumn and winter. About 63% of synoptic stations have increasing trends in the number of rainy days yearly. Significant trends in time series of number of rainy days and number of rainy days with equal to or greater than 1 mm mostly occur during spring and then in summer. But number of days with equal to or greater than 10 mm occurs mostly during these 3 seasons: summer, spring and winter. The greater daily of precipitation mostly occurs during summer. Results of studying average maximum temperature parameter in monthly scale showed an increasing significant trend in most of west, south west, and east stations of Iran for spring, summer and autumn. Also most of Iran shows increasing trend for annual average maximum temperature.
