WCRP Global Drought Information System Workshop (Frascati, 11-13 April 2012)
Poster on “Use of the multiple time scales SPI index for monitoring and forecasting drought events over the Mediterranean Basin”
Drought is a recurrent feature of climate and can affects areas with different climate regimes; its impacts depend on the duration, intensity and extent of precipitation deficiency and on the interaction between this extreme event and water demand for several purposes.
Due to the complexity of this phenomenon, several indices were developed to monitor the different types of drought, also according to the data availability.
In this study, the Standardized Precipitation Index (SPI) is selected in order to evaluate trends of drought events over the Mediterranean Basin interested by an increasing reduction of available water resources, for multiple time scales (1, 3, 6, 12 months).
This index is particularly suitable both because it requires only precipitation data and the standardization of the values permits a comparison between areas climatically and geographically different.
To obtain a spatiotemporal homogeneity of the SPI, the analysis is carried out using daily E-OBS (Ensamble Observational) gridded dataset from the ECA&D (European Climate Assessment & Dataset) project, covering the period from 1950 to the first half of 2011, with a resolution of 0.25 degree lat-lon grid.
A frequency computation of the SPI classes for each time scale gives information on the spatial distribution of these extreme events over the Basin and allows to highlight the most vulnerable areas. Furthermore the 3-month SPI are selected to point out potential seasonal trends; the analysis is made by calculating the frequency of the three negative SPI classes (moderately, severely and extremely dry) over sub-periods of 30 years, using a moving window method and comparing the number of occurrences of each sub-period.
This interannual study is crucial not only for understanding if exists an intensification of the drought phenomenon, but also for assessing if this intensification is focused on seasons of groundwater recharge.
Finally, the SPI can be used as a tool for drought forecast; after calculating the 1-month and 3-month SPI an “adaptive multi-regressive method” is applied to obtain monthly outlooks for the next 1-6 months, selecting potential predictors among a list of physical atmospheric indices and Sea Surface Temperature (SST) anomalies.
Magno R.1, Pasqui M.2, Guarnieri F.1,2, Gaetani M.2
1LaMMA – Environmental modelling and monitoring laboratory for sustainable development.
2IBIMET-CNR (Institute of Biometeorology of the National Research Council).
