Trend analysis of precipitation and drought in Basilicata from 1923 to 2000 within a southern Italy context

Series of annual, monthly and seasonal precipitation from 50 stations, distributed all over the Basilicata territory (southern Italy), were studied for the period 1923-2000. All the series were checked for homogeneity using MASH v. 1.0.1 software and the time series analysis was performed with the Mann-Kendall nonparametric test in order to detect possible trends. The results show that the annual total rainfall decreased by about 156 mm during the period investigated; the decrease becomes stronger in the last 30 years. There are considerably different trends for the different seasons. In particular, only the winter trend, which is downward, is statistically significant. In this season the total rainfall has decreased by about 133 mm. For this same period the standardized precipitation index (SPI) for multiple time scales of 12, 24 and 48 months has been computed. It appears that periods of drought have been quite frequent starting from 1975, with SPI ranging from about -1 to about -3. Copyright (C) 2004 Royal Meteorological Society.