Determining the temporal trend in annual maximum flood series in the Large Karoun river (Iran)

Annual maximum flood series in two main stations of Large Karoun river in Iran, measured during 1958 2009 period were examined to identify the temporal changes. Two approaches were used to evaluate the temporal changes in flood series during the period 1958-2009. The first approach is based on an analysis of standardized departures, and the second one is based on the multiple trend tests through varying the beginning and ending dates of the time series. Results indicate a noticeable step of increase in annual maximum flood series around 1983 relative to the gradual trend. The identification of an abrupt increase in annual maximum flood series rather than a gradual increasing trend is important because the implications of a step change are different from those of a gradual trend. The interpretation of a gradual trend is that the trend is likely to continue into the future, whereas the interpretation of a step change is that the climate system has shifted to a new regime that will likely remain relatively constant until a new shift or step change occurs.