Precipitation changes from two long-term hourly datasets in Tuscany, Italy

Over the last decades many studies revealed worldwide modifications in precipitation regimes and an increase in frequency and/or severity of extreme rainfall events. In central-northern Europe an increase in total rainfall amount and in the frequency of occurrences as well as in the amount of extreme daily precipitation was found. In the Mediterranean area, despite a decrease in rainfall amount, an increase in the fraction due to severe events was highlighted. Most studies used daily rainfall datasets to document temporal changes in precipitations, while few were carried out using hourly datasets. Investigating precipitation data at hourly rather than daily time scale can be important in terms of social, agriculture and hydrological/hydraulic impacts. Two long-term hourly rainfall datasets, collected at the sites of Viareggio and Vallombrosa in Tuscany, Italy, respectively over the periods 1948-2009 and 1930-2009, were digitalized and analysed to look for temporal changes in precipitation amount, frequency and intensity. Some hourly/daily climatic indices were calculated either at annual or seasonal scale; a quantile regression method was implemented and applied to look for trends and/or systematic changes in the data distribution. The main results showed a tendency to a decrease of total rainfall and wet hours, occurring in winter and spring, and to an increase of hourly average precipitation during wet hours. The percentage of hours with rainfall 75th percentile and <98th percentile and the precipitation fraction due to these events showed an increase, especially due to spring and autumn seasons. No significant changes were observed in the percentage of heavy rain hours (>98th percentile), even though a prevalence of positive trends was found.