Linking climate variations with the hydrological cycle over the semi-arid Central Andes of Argentina. Past, present and future, with emphasis on streamflow droughts.

4. RIVERA J.A., ARANEO D.C., PENALBA O.C., VILLALBA R

Viena

Congreso; EGU General Assembly 2017; 2017

In the Central Andes of Argentina (CAA, located between 28◦ and 38◦S), an arid to semi-arid region, the ir-rigation and a variety of socio-economical activities are highly dependent on river streamflows. Permanent andsemi-permanent rivers originate mainly from snowmelt and glacier ablation, enabling the development of largeagricultural oasis and the construction of numerous dams and reservoirs for irrigation and power generation. Mostof its 2.5 million inhabitants and the main economic activities are located in a small irrigated fraction of the ter-ritory, where the variations in the timing and amount of water resources largely determine the socio-economicvulnerability of the region. In this context, the links between climatic variability and the hydrological cycle wereassessed considering daily streamflow records from 21 streamgauges in the main rivers of the study area. Princi-pal component analysis of annual hydrographs from 1931 to 2015 allowed to discriminate between precipitation-and temperature-related components associated with variations in snow accumulation (51% of variance) and ad-vances/delays of the streamflow annual peak (16% of variance), respectively. The components related to intrasea-sonal variability account for 7% and 6% of variance, respectively, mixing both precipitation and thermal factors.The contribution of the precipitation-related component was the main driver of the 2010-15 streamflow droughtconditions, although the thermal contribution was relevant during specific seasonal drought events. Based on anempirical decomposition methodology we identified the main modes of streamflow drought variability, which arelinked to El Niño-Southern Oscillation on interannual time scales and the Pacific Decadal Oscillation (PDO) for thedecadal variations. This result shows the influence of the tropical Pacific Ocean in the development of streamflowdrought conditions and its relevance for potential predictability of hydroclimatic variations over the region. Nev-ertheless, recent studies indicate that, besides the contribution of La Niña and PDO signals, anthropogenic climatechange could be responsible for the development of regional extreme drought conditions. In fact, reconstructionof CAA hydroclimate based on centennial-long tree-ring records shows a recent declining precipitation trend thatis also evident over North Patagonia (38◦-45◦S) reconstructions, unprecedented in the last ∼400 years. This de-creasing trend can be linked to the broadening of the sub-tropical dry zones as a displacement of the descendingarm of the Hadley Cell circulation, a phenomenon likely forced by increased greenhouse gas concentrations, al-though its underlying mechanisms still not well understood. The assessment of future drought conditions basedon a CMIP5 multi-model ensemble forced under two scenarios (RCP4.5 and RCP8.5) shows an expected increasein the number of drought events, with a decrease in the mean drought duration and non-significant changes inmean drought severity, although these results have a high range of uncertainty and are dependent on the futuretime horizon and selected scenario. Moreover, projected temperature trends will shift the streamflow peak fromsummer to late spring, in combination with a decrease in snow accumulation that will decrease the annual cycleamplitude. Both factors will likely change the hydroclimate of the semi-arid Andes, calling for new and improvedwater management practices over the region.