Assessing the severity and duration of the recent hydrological drought (2010-2015) across the Central Andes of Argentina in a climate change context.

JUAN ANTONIO RIVERA; OLGA PENALBA; RICARDO VILLALBA; DIEGO ARANEO

Canmore

Conferencia; 8th GEWEX Open Science Conference: Extremes and Water on the Edge; 2018

World Climate Research Programme

During the period 2010?2015, the semi-arid Central Andes in Argentina (CAA, located between 28 and 38°S) experienced one of the most severe and long-lasting hydrological droughts on record. Since the snowmelt is the most important source of water, the reduced snowfall over the mountains propagated the drought signal through the streamflows in the adjacent foothills east of the Andes ranges. Motivated by the widespread impacts on the socio-economic activities in the region, this study aims to characterize the recent hydrological drought in terms of streamflow deficits. Based on streamflow data from 20 basins, we used the standardized streamflow index (SSI) to characterize hydrological droughts during the period 1971?2017. We found that the regional extent of the 2010?2015 hydrological drought was limited to the basins located north of 38° S, with mean duration of 67 months and maximum drought severity exhibiting a heterogeneous pattern in terms of spatial distribution and time of occurrence. The drought event reached extreme conditions in 14 of the 15 basins in the CAA, being record-breaking drought in six of the basins. This condition was likely driven by a cooling in the tropical Pacific Ocean resembling La Niña conditions, which generated a decrease in snowfall over the Andes due to suppressed frontal activity.The comparison of this drought with major droughts of the past century shows that, in terms of duration, the 2010-2015 hydrological drought was the longest on record (1909-2017) along the CAA. Regarding drought severity, this event had record-low streamflow levels recorded in several basins of the region. During the winters of 2016 and 2017, snow accumulation over the Andes was below average, triggering again hydrological drought conditions in 6 of the 15 basins in the CAA (up to July 2017), a value that is expected to increase considering the time lag of the drought propagation through the hydrological cycle.The assessment of future drought conditions based on a CMIP5 multi-model ensemble forced under two scenarios (RCP4.5 and RCP8.5) shows an expected increase in the number of drought events, with a decrease in the mean drought duration and non-significant changes in mean drought severity, although these results have a high range of uncertainty and are dependent on the future time horizon and selected scenario. Moreover, projected temperature trends will shift the streamflow peak from summer to late spring, in combination with a decrease in snow accumulation that will decrease the annual cycle amplitude. Both factors will likely change the hydroclimate of the semi-arid CAA, calling for new and improved water management practices over the region.