ABSTRACT
Frequency analysis is an important method in hydrological statistics, which has been applied in uncertainty assessment of hydrological process extensively, such as flood control, drought resistance, and safety design of water conservancy project (Franks and Kuczera, 2002; Saf, 2009; Xu et al., 2010; Yoo et al., 2005). This method serves many purposes in statistical data analysis by fitting a Probability Distribution Function (PDF) to a series of observations. Then, the fitted PDF provides summary information about the data, and allows predictions beyond the range of data used for parameter estimation. This prediction is based on the information of past events in order to define the probabilities of future events. Therefore, the prediction is attached a risk of failure. The frequency analysis does not predict the future with certainty, but it provides good models for explaining and making efficient use of the events that had occurred in the past (Khaliq et al., 2006; Smakhtin, 2001; Yang et al., 2010).
