Meteorological drought characteristics in the historical period and in future climate model projections - a regional analysis

Droughts are a natural phenomenon and occur when there is a more or less prolonged period with minimal precipitation, either due to a decrease in the amount of rainfall or a change in the timing of rainfall events, from a "normal" value (meteorological droughts). It is essential to study the present and future characteristics of mete-orological droughts on a regional scale, taking into account both natural climate variability and climate change, for assessing their impact on the availability of water resources. This study presents findings on the identification and quantification of droughts in the northern part of the Tus-cany region (Italy) using the Standardized Precipitation Index (SPI) at different time scales. The analyses were carried out by considering the longest available historical rainfall datasets from stations in the study area, as well as climate projections generated by General Circulation Models (GCMs) and Regional Climate Models (RCMs). The rainfall data were processed to determine the normalized values of the cumulative rainfall over various time windows (SPI). The study confirmed that the SPI index well reflected the historical water shortages observed in the area of interest. The analysis of the historical precipitation showed an increase in the frequency, duration and severity of droughts during the thirty-year period 1983-2012 when compared to the period 1938-2012; the decade 2003-2012 was identified as particularly concerning. By statistically analysing the rainfall data provided by the RCM models, this study found that the frequency, severity and duration of drought episodes were similar to those that occurred during the critical decade 2003-2012. Thus, it is likely that in the future the area will experience comparable episodes of rainfall deficit both in the medium- and long-term, and for both the analysed climate scenarios: RCP4.5 and RCP8.5. However, exceptional drought events in terms of severity and duration cannot be excluded.