Drought severity-duration relationships in Northern Argentina during the last 50 years

Due to the increasing demand on surface water resources, it is necessary an assessment of the rainfall deficit conditions. Particularly, northeastern Argentina is part of the La Plata Basin, environment of great economic and demographic significance, and the impacts of droughts on hydrology and agriculture are immediate. The main goal of this research is to present an analysis of the severity-duration relationships of the dry periods occurred during the last 50 years. These dry periods were identified by an index that considers the monthly anomalies in the number of dry days filtered using a moving average with a 12-month window. This index was applied to each of the 51 rainfall stations used, whose daily rainfall data were provided by the CLARIS LPB Data Base and has less than 10% of missing values. The behavior of the dry episodes was analyzed during the sub-periods 1960-1974, 1975-1990 and 1991-2008 by severity-duration curves. It was verified that the decadal variability plays an important role in modulating the dry periods. An analysis of the temporal variabilities of the annual number of dry days showed that, in some regions, periodicities between 8 and 24 could be associated with the changes observed in the severity-duration relationships. The maximum values of duration were recorded during the 1960-1974 period for a great portion of the region, while the major extension of the maximum severity values were observed during the 1975-1990 period. Also, the 1991-2008 period showed a trend towards drier conditions, which was verified by the regional analysis of the annual number of dry days. The drought of 2008-09 was the most extreme in several stations of the country, which warrants a continuous regional monitoring of the evolution of these adversities and its long term trend.