DDF-curves updating in climate change scenarios for Southern Italy

Abstract

Recently trends in extreme rainfall were investigated on the global, regional and local scales. On the global scale, there is robust observational evidence that the frequency and intensity of extreme events significantly changed over the last decades. For this reason, climate change effects on extreme rainfall should be accounted in the design of hydraulics infrastructures, in particular in the definition of rainfall depth-duration-frequency (DDF) curves. The purpose of this study is to provide an assessment of the effects of statistically significant trends in extreme rainfall on the rainfall depth-duration-frequency (DDF) curves for the return periods typically used in the design of urban drainage systems. The methodology proposed in this study was applied in Southern Italy, specifically in Sicily. Firstly, the detection and quantification of trends in the annual maximum rainfall series of different durations, recorded in 65 rain gauges over the 1950-2008 period, were carried out. For each duration, the moving averages were computed and then the Mann-Kendall test was applied. Results showed that, for all the durations, increasing and decreasing trends occurred over the examined period. The generalized extreme value distribution (GEV) has been employed to compute extreme rainfall with return periods equal to 5, 10 and 20 years. The magnitude of statistically significant trends were used in order to modify the GEV parameters and define the DDF curves in some climate scenarios. The study highlighted the need to revise and update design criteria to account for potential future variations of extreme rainfall due to climate change.