Estimation of Changes in Empirical Probability and Cumulative Distribution Function of Annual Maximum Instantaneous Flood Peak Discharge

Annual maximum discharge time series is a very important series for hydrological planning and design. Various factors such as changes in climate, land use and land cover as well as other human affected activities can affect the characteristics of this series, therefore estimation of changes of its characteristics is an applied research. The objective of this study is evaluation of changes in empirical probability distribution function (EPDF) and the empirical cumulative distribution function (ECDF) of annual maximum discharge time series on the basis of a novel approach. For this purpose, three annual maximum instantaneous flood peak discharge time series belonging to Araz-Kouseh, Lazoureh and Tamer hydrometry stations with 43 years recorded data located in Golestan province are used. The results indicate that estimated changes in the studied series occurred in upper quantiles. It is clear the changes pattern of EPDF and ECDF curves were different during their periods. The Araz-Kouseh ECDF curve of last year did not show certain change in comparison with its first year curve while Tamer and Lazoureh series show a lot of changes in upper level of maximum discharge respectively. Comparison of first and last years EPDF curves show the domains of Araz-Kouseh EPDF curves are relatively constant but they experienced significant increase in Tamer and Lazoureh series. In addition the last year EPDF modes increase relative to the corresponding values in first year EPDF in all of three series. The probability values corresponding to the modes had limited changes for Araz-Kouseh series while experienced considerable increase for other two series.