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

A deficit of precipitation has different impacts on the ground water, reservoir storage, soil moisture, snowpack, and streamflow. In this study spatial and temporal patterns of drought in a region of southern Italy (Calabria region) have been analysed. First, the original database was homogenised and the gaps filled in for 129 daily rain gauges for the 1916-2006 period. Then both the short-time (3, 6 and 9 months) and long-time (12 and 24 months) Standardized Precipitation Index (SPI) was estimated to analyse drought especially from the agricultural point of view. A time series analysis was performed with the Mann-Kendall nonparametric test to detect possible trends. A generally negative trend has been detected. Running trend analysis, carried out for long-time SPI, revealed that the previously discussed tendencies were not persistent throughout the series length, but depended on the period examined. SPI data were interpolated and mapped using a geostatistical approach. Moreover, both the short- and long-time SPI data were analysed by using Factor Kriging Analysis (FKA) to identify and map regionalized factors at different spatial scales from the point of view of SPI.