Trends of Mean and Extreme Precipitation in Southern Italy

A modification in water cycle is one of the most noticeable consequences of global atmospheric warming. Precipitation is a key point in the hydrological process and the distribution of extreme rainfall is particularly important because it may impact on water management, soil erosion and flash floods. In this paper, an analysis of mean and extreme rainfall over a region of southern Italy (Calabria) has been carried using a daily homogeneous precipitation dataset of 129 rain gauges with more than 50 years of observation for the period 1916-2006. First, a statistical analysis was performed through the Mann-Kendall test in order to detect possible trends at annual, seasonal and monthly scale. Then, a set of indices derived from the daily homogeneous rainfall time series was defined and used to examine changes in extreme rainfall through nonparametric techniques. Results show a decreasing trend for annual and winter-autumn precipitation and an increasing trend for summer precipitation. Moreover, a prevailing decreasing trend of the various indices has been detected. These results appear to be in contrast with previous large scale studies which evidenced an increase in extreme rainfall and a decrease in the yearly totals, in other areas of Southern Europe. These differences in the behaviour of extreme rainfall suggest that a detailed regional analysis is always necessary because the distribution of extreme precipitation is often linked to the morphological settings of a territory (proximity to the sea, presence of reliefs, etc.).