UNCERTAINTIES AND TRENDS IN EXTREME RAINFALL SERIES IN TUSCANY, ITALY- EFFECTS ON URBAN DRAINAGE NETWORKS DESIGN

Sound basin management at urban or greater scale needs reliable design storm definition. A statistical analysis is carried out on extreme an nual. rainfall series for durations of 1, 3, 6 and 12 hours occurring at two gauges in Tuscany, Italy. Kendall's test is applied to the extr emal series to detect a definite increasing (or decreasing) trend. A s pecial form of an ARIMA model is also fitted to the series to quantify possible linear trends and their respective significance. Results sho w a clearly increasing trend at shortest duration at both gauges, no t rend at longer ones. Time evolution of design storms for all durations and return periods up to 25 years is derived and analysed based on Gu mbel distribution. Applications are presented concerning impacts of un certainties for the design of urban drainage networks. (C) 1998 Publis hed by Elsevier Science Ltd. All rights reserved.