Uncertainty Analysis in the Evaluation of Extreme Rainfall Trends and Its Implications on Urban Drainage System Design

Vincenza Notaro,Goffredo La Loggia,Gabriele Freni,Lorena Liuzzo

doi:10.3390/w7126667

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https://doi.org/10.3390/w7126667

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Abstract

Future projections provided by climate models suggest that the occurrence of extreme rainfall events will increase and this is evidence that the climate is changing. Because the design of urban drainage systems is based on the statistical analysis of past events, variations in the intensity and frequency of extreme rainfall represent a critical issue for the estimation of rainfall. For this reason, the design criteria of drainage systems should take into account the trends in the past and the future climate changes projections. To this end, a Bayesian procedure was proposed to update the parameters of depth–duration–frequency (DDF) curves to assess the uncertainty related to the estimation of these values, once the evidence of annual maximum rainfall trends was verified. Namely, in the present study, the historical extreme rainfall series with durations of 1, 3, 6, 12 and 24 h for the period of 1950–2008, recorded by the rain gauges located near the Paceco urban area (southern Italy), were analyzed to detect statistically significant trends using the non‐parametric Mann‐Kendall test. Based on the rainfall trends, the parameters of the DDF curves for a five‐year return period were updated to define some climate scenarios. Finally, the implications of the uncertainty related to the DDF parameters estimation on the design of a real urban drainage system was assessed to provide an evaluation of its performance under the assumption of climate change. Results showed that the future increase of annual maximum precipitation in the area of study would affect the analyzed drainage system, which could face more frequent episodes of surcharge.

Highlights

Changes in the hydrologic cycle due to the increase in atmospheric greenhouse gas concentrations cause variations in intensity, duration, and frequency of precipitation events [1,2]
The main purpose of the present study is to provide a methodology to incorporate the effects of extreme rainfall variations on DDF curve evaluation and to assess the uncertainty related to the estimation of these curves
The results obtained from the analysis of the extreme rainfall data are summarized in Table 1, where the level of significance of trend α, the magnitudes β and the p‐values have been reported for each duration and rain gauge

Summary

Introduction

Changes in the hydrologic cycle due to the increase in atmospheric greenhouse gas concentrations cause variations in intensity, duration, and frequency of precipitation events [1,2]. The potential effects of climate change on rainfall extremes widely affect the design of storm water management structures. This issue is critical because variations in extreme rainfall may be larger than those of average estimates [3]. In the context of climate change occurring, rainfall intensities could be increased, which would lead to an additional impact on drainage systems, due to the alteration of magnitude and frequency. Considering the potential effects of climate change on extreme rainfall can improve the results of the several methodologies aimed at evaluating potential flood risk and related damages in urban areas [5,6,7] or at supporting decision making for flood risk management [8]

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