Extreme Rainfall Nonstationarity Investigation and Intensity-Frequency-Duration Relationship

Nonstationary behavior of recent climate increases concerns among hydrologists about the currently used design rainfall estimates. Therefore, it is necessary to perform an analysis to confirm stationarity or detect nonstationarity of extreme rainfall data to derive accurate design rainfall estimates for infrastructure projects and flood mitigation works. An extreme rainfall nonstationarity analysis of the storm durations from 6min to 72h was conducted in this study using data from the Melbourne Regional Office station in Melbourne, Australia, for the period of 1925-2010. Stationary generalized extreme value (GEV) models were constructed to obtain intensity-frequency-duration relationships for these storm durations using data from two time periods, 1925-1966 and 1967-2010, after identifying the year 1967 as the change-point year. Design rainfall estimates of the stationary models for the two periods were compared to identify the possible changes. Nonstationary GEV models, which were developed for storm durations that showed statistically significant extreme rainfall trends, did not show an advantage over stationary GEV models. There was no evidence of nonstationarity according to stationarity tests, despite the presence of statistically significant extreme rainfall trends. The developed methodology consisting of trend and nonstationarity tests, change point analysis, and stationary and nonstationary GEV models was demonstrated successfully using the data from the selected station.