Regional aspects of drought in southern South America

JUAN ANTONIO RIVERA; OLGA PENALBA

Montevideo

Conferencia; WCRP Conference for Latin America and the Caribbean: Developing, linking and applying climate knowledge; 2014

World Climate Research Programme

Droughts are regional in nature and commonly cover large areas and extend for long time periods. Therefore, it is important to study such events within a regional context. This study aims assess the regional aspects of drought temporal variabilities in southern South America (SSA) for the period 1961-2008. In order to define drought conditions, we used the standardized precipitation index (SPI), which is a simple, powerful and flexible index that was widely used in SSA. The SPI was calculated at time scales of 3 (SPI3) and 12 months (SPI12), which represents short- and long-term droughts, respectively. Rotated principal components analysis was used to identify spatially homogeneous regions with different precipitation temporal variabilities. We obtained for both time scales seven homogeneous regions, which are climatically consistent. Based on the regional SPI, drought mayor events were identified in the decades of 1960 and 1970 in most of the regions, although some record breaking events were recorded during recent decades. Spectral and wavelet analysis were used to identify the main modes of variability for each region. The regional SPI3 time series are characterized with significant seasonal variabilities; while the SPI12 time series possess significant inter-annual variabilities in the range of 1 to 5 years. In order to identify the regional influence of El Niño and La Niña events on the SPI time series, we calculated the mean SPI values for the El Niño and La Niña years and assessed its significance through bootstrap analysis. We found coherent and significant SPI responses to ENSO phases in most of the seven regions, mainly for the SPI12 time series. The precipitation response to La Niña events is characterized with precipitation deficits, identified with negative values of the SPI, although the signal is not as clear as in the cases of El Niño events. Lagged correlations between the SPI regional time series and the Niño 3.4 index were performed in order to identify the potential of the ENSO signal for seasonal forecasting. The ENSO related indices can be useful for seasonal and inter-annual drought forecasts, and together with a regional drought monitoring system will be extremely helpful for drought preparedness and early warning.