Identify Trend in the Annual Temperature and Precipitation in Karkheh River Basin

Temperature and precipitation are the main components of climate forming which their variation can change the climate structure of each site. This study investigated the temporal and spatial variations of temperature and precipitation in the Karkheh Basin, located in the West of Iran. For this purpose, after checking thehomogeneity and accuracy of data, 22 synoptic and meteorological stations over the 1971-2011 periods were selected. The objective of this study is evaluating the changes in temperature and precipitation time series by Mnn-Kendall, Spearman tests and Sen’s slope estimator. Results showed significant increasing and decreasing trends in the annual temperature and precipitation, respectively, with significant levels of 1 and 5 percent for most of the stations. The magnitude of the significant positive trends of annual temperature changed from (+) 0.12 °C/decade at Khrromabad to (+) 0.61 °C/decade at Kermanshah. The maximum and minimum annual precipitation decreasing trend was observed at Ghourbaghestan station located in the Kermanshah province and Dehnoud station, with slope of (-) 8/77 mm/year and (-) 1/27 mm/year, respectively. In special pattern, almost all stations in the eastern part of the Karkheh basin showed non-significant trend in precipitation. The most significant decreasing changes was observed in the West and South parts of Karkheh basin although the decreasing of precipitation in central and eastern parts was seen but this trend was not significant. Generally, the detection trend changes, except for exceptional cases, are consistent with recent findings of global studies.