Spatio-temporal validation of the Standardized Precipitation Index of the VAMOS atlas of extremes, with emphasis in drought events in Southern South America

OLGA PENALBA; JUAN ANTONIO RIVERA

San Francisco

Encuentro; American Geophysical Union Fall Meeting; 2011

American Geophysical Union

The aim of this research is to validate the spatio-temporal variability of droughts in Southern South America (south of 20°S) depicted by the VAMOS atlas of extremes trough the Standardized Precipitation Index (SPI). In the study region, droughts are a recurring climatic phenomenon, with periodicities that vary regionally. Monitoring of these extreme events and the development of early warning systems provide information necessary to make timely decisions on the management of water resources. The SPI quantifies the number of standard deviations that the accumulated rainfall in a given time scale deviates from the average value of a location in a particular period. This drought index has been used to quantify deficits in water resources and as a drought monitoring tool in several regions of the world. In order to build this index, monthly rainfall data were obtained from the CLARIS LPB Data Base for 81 of its stations, which were subjected to quality control procedures and have less than 10% of missing values. We used the 1981-2008 common comparison period. This allows comparing the performance of the SPI based on both CDC and CPC gridded observations and the MERRA and CFSR reanalysis. The validation was performed for the time scales used in the atlas (3, 6, 12 and 24 months), which gives a broad approach of the different precipitation shortages. We focused the comparison on the extreme events of 1988-89 and 1995-96. The SPI maps and time series of the atlas of extremes are consistent with the results based on non-gridded precipitation data. The spatial behavior of the SPI during the selected drought events is quite accurate and captures much of the variability shown in the observations. The performance of the SPI in the Patagonia region is remarkable. The time series of East Argentina and Uruguay & Southeastern Brazil regions shows similar behaviors, but high frequency variabilities are missed. These variabilities could be important for the forecasting of droughts on seasonal scales. Moreover, the observations at the time scales of 12 and 24 months indicate for both regions that the 1988-89 drought was more severe than the 1995-96 event. This was verified for the Uruguay & Southeastern Brazil region but for the East Argentina region CPC and CFSR reanalysis shows an opposite behavior. We also plan to use these results for the validation of model outputs and other global and continental monitoring systems based in gridded precipitation data.