Climate Change Detection and Green House Gases Attribution to it Using AOGCMs Models and Two-Dimensional Normal Distribution (Case Study; Large Karoon River Basin)

In most climate change studies, the first step is to detect climate change and to attribute the causes. In this study we attempt firstly to detect the trends of temperature and precipitation of Large Karoon basin in and secondly discover the main cause(s) of the detected trends (e.g. trends due to internal forcing or greenhouse gasses). Then the range of variability due to internal forcing such as interactions between each elements of climate system (e.g. atmosphere, biosphere, cryosphere and …). The temperature and precipitation of control runs of two different AOGCMs (HadCM3 and CGCM3) were extracted from IPCC website that contains 1000-year of monthly data. Based on these data, the range of internal variability of temperature and precipitation of the basin were calculated using two-dimensional normal distribution. Results showed that, with 95% confidence the temperature anomaly of the basin is less than 1.5oc and the precipitation anomaly is less than 70%. The range of internal variability was compared with the observed temperature and precipitation analomies of Karoon basin in past periods. The results showed that for the past 50 years, the trend of temperature is positive and the trend of precipitation is negative. On the other hand the recent years are located outside the range of internal variability which means the impact of climate change on Karoon basin is meaningful for these years.