Changes in daily precipitation frequency and distribution in Italy over the last 120 years

A new data set of 45 daily precipitation series, covering quite uniformly Italian territory for the period 1880–2002, was recovered. The series have been homogenized on daily basis, completed by means of statistical methods and grouped into five regions by a Principal Component Analysis. Seasonal and yearly total precipitation, number of wet days, and precipitation intensity were analyzed for each station record and averaged into five regional series for a synthetic description of the results. Proportion and frequency of daily rainfall amounts, belonging to six precipitation class-intervals, defined on the basis of some percentiles of the precipitation distribution, were also analyzed. The results show a negative significant trend in the number of wet days all over Italy, and a positive trend in precipitation intensity, which is significant only in the northern regions. The negative trend in wet days has persisted since the end of 19th century and is due to the marked decrease in the number of low intensity precipitation events. An increase in the number of events belonging to the highest intensity class interval was observed too, but only in northern regions.