Precipitation intensity trends in northern Italy

Recent studies on changes in precipitation intensity encompassing North Ame rica have found evidence for an increase in the relative amount of precipit ation contributed by heavy and extreme rainfall events in the last 80 years . Within this context, the purpose of this paper is to verify whether such a signal can also be detected in northern Italy, where daily precipitation data are available from the beginning of the 19th century. The analysis is performed by applying the non-parametric Mann-Kendall test to mean anomaly series obtained through averaging the anomalies of some precipitation inten sity statistics over five stations: Genoa (1833-1998), Milan (1858-1998), M antova (1868-1997), Bologna (1879-1998) and Ferrara (1879-1996). It provide s evidence that in northern Italy, the number of rainy days has a stronger and more significant negative trend than the corresponding precipitation am ount, both on a yearly basis and in all of the seasons. As a consequence, p recipitation intensity has a positive trend. The increase in precipitation intensity causes a significant positive trend in the proportion of total pr ecipitation contributed by heavy precipitation events (i.e. daily precipita tion > 25 mm and daily precipitation > 50 mm). The trend is mainly caused b y the last 60-80 years, and is particularly evident in the periods of 1930- 1945 and 1975-1995. The increase in precipitation intensity is connected to a modification of the distribution of daily precipitation values in a year , with trends that grow from the lower to the upper percentiles, and up to 4 mm/100 years for the 95th percentile. Copyright (C) 2000 Royal Meteorolog ical Society.