Frequency analysis assumes that extreme rainfall and flood values are generated from independent and identically distributed random variables. If a data series is nonstationary with trend or step change, the fundamental assumption for frequency analysis will be seriously challenged, and this will have tremendous implications for probability assessments of the magnitude and frequency of future floods. There are several statistical tests available for identifying the nonstationarities in the rainfall or flow records.
Keywords: time series, nonstationarity, trend test, step change test, periodic test