Modelling drought severity at different timescales using Standardized Precipitation Index and Geostatistics: an application in southern Italy

A deficit in precipitation has different impact on ground water, reservoir storage, soil moisture, snowpack, and streamflow. In this study, spatial and temporal drought patterns in a region of southern Italy (Calabria) have been analysed by means of a homogenous monthly precipitation data set of 129 daily rain gauges for the 1917-2006 period, with no lack in the data. First, both the short-time (3, 6 and 9 months) and the long-time (12 and 24 months) Standardized Precipitation Index (SPI) were estimated to analyse drought especially from an agricultural point of view. Then, in order to characterize the SPI spatial pattern, index data of a severe event were interpolated and mapped using a geostatistical approach. Finally, a time series analysis was performed with the Mann-Kendall non-parametric test to detect possible trends. Results showed that several heavy drought episodes have widely affected the Calabria region and, among the most recent events, the drought occurred after 1980 was the worst in terms of spatial extent. A generally negative trend has been detected and the running trend analysis, carried out for the long-time SPI, revealed that the tendencies previously discussed were not persistent throughout the series length, but depended on the period examined.