Impact of climate variability and change on meteorological droughts over Southern South America

JUAN ANTONIO RIVERA; OLGA PENALBA; DIEGO ARANEO

Paris

Conferencia; Our Common Future Under Climate Change International Scientific Conference; 2015

Centre National de la Recherche Scientifique (CNRS)

Droughts are perceived as one of the costliest and least understood natural disasters, given the difficulty in defining its beginning and end, its slow development and its multiple regional aspects. Southern South America (SSA) was no exception to this hazard, whose impacts were evident in the reduction in crop yields, reduced cattle products, streamflow deficiencies and consequently problems for hydroelectric power generation. This research addresses the observed spatial and temporal variability of precipitation and meteorological drought over SSA during the 20th century, and the expected impacts of climate change on these variables. The Standardized Precipitation Index (SPI) was used as a short- and long-term drought indicator, given its suitability for the study region. Observed trends in the area affected by drought conditions were assessed through a non-linear approach based on the residual of the empirical mode decomposition, a recently proposed methodology which is robust in presence of non-stationary data. Trends indicate the existence of a low-frequency variability that modulates regional precipitation patterns at different temporal scales, and warns about possible future consequences in the social and economic sectors if trends towards an increase in the drought affected area continue. This non-linearity was also evident on the temporal behavior of other hydrometeorological variables, like the annual number of dry days over Argentina, and on the streamflow deficiencies over the central Andes and Patagonia. Moreover, links with decadal oscillations as the PDO were identified in the modulation of the decadal component of the annual cumulated deficit volume in the central Andes of Argentina. The future assessment of precipitation and meteorological drought conditions was performed through a CMIP5 multi-model ensemble based on 15 Global Circulation Models (GCMs) forced under two future scenarios (RCP4.5 and RCP8.5). Changes in meteorological drought characteristics were identified by the difference for early (2011-2040) and late (2071-2100) 21st century values with respect to the 1979-2008 baseline. Future climate conditions are expected to modify the regional characteristics of meteorological droughts over SSA, but the range of uncertainty in the expected changes is high. A significant increase in the number of drought events for most of the 21st century sub-periods and scenarios is projected for the multi-model ensemble outputs. The mean duration of drought events will be shorter, with no significant changes in the severity of droughts and the occurrence of multi-decadal changes in the number of critical dry months is likely, although the significance in the changes depends on the region, future time horizon and scenario. These results overlap with a projected increase in precipitation over most of the regions, which has a strong seasonality and, therefore, will have some implications upon the future meteorological drought developments and the agricultural and hydrological practices in SSA. It is expected that the outcomes of this study will provide a measure of the likelihood of further drought changes under the CMIP5 framework, which was a key factor of the IPCC?s AR5.