Analysis of the Changes of Return Period under the Nonstationary Conditions

Frequency analysis for nonstationary hydrologic data due to climate change has been growing for the last several decades. However, little attention has been given to analysis for the return period under the nonstationarity. This paper is intended to analyze the change of return periods for hydrologic extreme events under nonstationary conditions. There are two definitions of return period under nonstationarity. One is the expected waiting time and the other is the expected number of an exceedance event. In this study, the nonstationary Gumbel models are used in order to perform nonstationary frequency analysis. The change of return period with two definitions of the return period is analyzed under nonstationary conditions. As a result, there are differences of return periods between stationary and nonstationary conditions. In addition, there are also differences between two definitions of return period.