Changes in daily precipitation extremes in the Mediterranean from 1951 to 2010: the Basilicata region, southern Italy

Changes in precipitation extremes for the Basilicata region, southern Italy, have been analyzed using data from 55 precipitation stations with complete daily time series during the period 1951-2010. All the series were submitted to quality control assessment and homogenization. To detect possible trends the time series analysis was performed with the Mann-Kendall non-parametric test. The annual and seasonal total precipitation underwent a general downward trend over the period 1951-2010 mainly due to the autumn-winter decrease of precipitation, although the tendency for the last decade is clearly positive. The precipitation intensity shows a general positive trend, mainly due to the upward trend of spring. The dry spell mean has increased throughout the region over 1951-2010, even if a really important opposite trend characterizes the last decade. The wet spell mean has decreased throughout the region from 1951 to 2010, although a strong inversion of tendency has been recorded in the last 10years. Trends in the extreme daily precipitation have indicated a general downward tendency, mainly during the summer season. The analysis of multi-day sequences of moderate to heavy rainfall has indicated a corresponding increase in their frequency and intensity, especially in the last decade. The overall results indicate a present hydroclimatic regime characterized by an increase in total rainfall and precipitation intensity and a small decrease in dry spell lengths. The positive change in precipitation magnitude is due to multi-day extreme precipitation rather than to single-day precipitation. This last observation is very important for its huge hydrological impact on the environment. In Basilicata, the increase in intensity/frequency of multi-days extreme events has led to the growth of severe flooding and landsliding events, not only in autumn and winter, but even in the early spring.