Spatial variability of drought: An analysis of the SPI in Sicily

An analysis of drought in Sicily from 1926 to 1996 is presented. In identifying drought over the region, both the NCEP/NCAR reanalysis precipitation data and those observed in 43 gauges, located quite uniformly over the territory of the Island, are used. Drought occurrence is estimated by means of the Standardized Precipitation Index (SPI). To study long-term drought variability, a Principal Component Analysis was applied to the SPI field. Results suggest that the entire Island is characterised by a drought variability with a multi-year fluctuations and a tendency towards drier periods from the seventies onward. A preliminary comparison between results obtained using the meteorological large-scale analysis and that derived from actual observations on the ground shows a general good agreement, although further efforts are needed to get a better downscaling of the large-scale precipitation fields. Furthermore, by applying orthogonal rotations to the principal component patterns, it has been found that three distinct areas having coherent climatic variability may be identified. Finally, the sensitivity of the SPI values on the calibration period is also investigated.