Investigation of Precipitation and Temperature Trend Across the North West of Iran in Recent half of the Century

Temperature and precipitation are two main factors of climate and their variation may lead to change the climate of every region. For this reason¡ investigation of rainfall and temperature trend¡ in different temporal and spatial scales¡ forms a large part of climatology and water resources engineering researches. In this study¡ trends of temperature and precipitation of the NW of Iran (10 synoptic stations) were examined in monthly¡ seasonal and annual time scales in the period of 1961-2010 using the Mann-Kendall method after the removal of the effect of all significant autocorrelation coefficients. The Sen''s slope estimator was used for determining the slope of temperature and precipitation trend line. Results showed that there is a positive trend in the most of months for the NW of Iran''s temperature. The most numbers of stations with significant positive trend were observed in April and September. In the case of precipitation¡ the monthly series showed a decreasing trend. In seasonal time scale¡ summer¡ winter and autumn seasons have experienced the highest increase in temperature¡ respectively¡ and spring and winter seasons have the highest negative rate in precipitation. In annual time scale¡ 60% of stations have experienced a significant positive trend in temperature which it led to a negative trend in precipitation of 70% of considered stations. In average¡ across the North West of Iran in the recent half of the century¡ the temperature increased about .20 °C and the precipitation decreased about -88.9 mm.