ACQUISITION AND ANALYSIS OF HISTORICAL SERIES OF HOURLY PLUVIOMETRIC DATA

The present research can represent a significant step forward due to the acquisition and analysis of historical time series of higher than usual frequency data (hourly), which allows to perform far more robust and significant statistical analysis of the variability and tendencies of the extreme storms, as well as the droughts. Two long historical series of hourly precipitation data were digitalized starting from analogical records, collected in Tuscany, Italy, one next to the coastline, the other over the inland mountains, covering 1945-2002 and 1930-2005, respectively. Data quality as well as homogeneity were checked by means of few statistical tests, such as the run test, including the comparison with data colleted at nearby rain gauges. The analysis of the overcomes of specific hourly thresholds, computed on the basis of the reference period 1961-1990, has shown significant increases at both sites in the latest 15 years with regards to the previous times, as well as an increased seasonality, resulting in the concentration of the most intense and extreme rainfalls in September-November. A significant decrease of the number of rainy hours was observed at both sites , mainly due to winter drying and, limited to the mountainous gauge, a relevant increase of the average hourly precipitation intensity. The analysis of reference percentiles for the hourly precipitation, such as, 99°, 99,5° e 99,9°, has shown positive trends at both sites, as well as the precipitation series consisting of 3, 6, 12 and 24 consecutive hours events. As a preliminary attempt to understand the findings, the tendencies of heavy sub-daily rainfalls was compared to the sea surface temperature (SST) time series, leading to partially significant outcomes and paving the way to further research.