Trends in the daily intensity of precipitation in Italy from 1951 to 1996

An analysis of 67 sites of daily precipitation records over the 1951-1996 p eriod for Italy is presented. Seasonal and yearly total precipitation (TP), number of wet days (WDs) and precipitation intensity (PI) are investigated , and the trends both for the single station records, and for some differen t area average series are studied. PI is analysed by attributing precipitat ion to ten class-intervals, removing the influence of variations in the num ber of WDs to yield changes in the underlying shape of the WD amount distri bution. The results show that the trend for the number of WDs in the year i s significantly negative throughout Italy, stronger in the north than in th e south: this trend is mainly a result of the winter. Moreover, they show t hat there is a tendency toward an increase in PI. This increase is globally less strong and significant than the decrease in the number of WDs. It is not concentrated in one specific season, but changes from area to area, and is generally weak in winter, due to a significant decrease of winter TP. I n northern Italy, the increase in PI is mainly owing to a strong increase i n the heaviest events, while in central-southern Italy, it depends on a lar ger part of the distribution of WD amounts. The analysis of the evolution o f the class-interval contributions shows that the positive trend of the hea viest events starts in the 1970s, as does the negative trend of lightest ev ents. Copyright (C) 2001 Royal Meteorological Society.