Hydrological drought assessment over the Argentinean Andes. Links with intra-seasonal to inter-decadal climate variations

RIVERA J, PENALBA O.C, ARANEO D.,

Simposio; International Expert Symposium: ?Coping with Droughts? - ?Building a Community of Practice on Drought Management Tools?; 2014

The periods of time when streamflows are below a critical level are extreme adverse conditions that may have significant implications for society, economy and environment. In order to characterize these events at the regional level, we conducted a climatological study of hydrological droughts over the Andean rivers of Argentina. Monthly and daily streamflow data were used from 21 gauging stations distributed between latitudes 30°S and 50°S, from the San Juan River to the Santa Cruz River, with measurement periods ranging from 40 to 110 years. Two methodologies were applied at monthly and daily basis in order to depict the main characteristics of streamflow droughts and deficiencies, respectively. The Standardized runoff index (SRI) was applied to the monthly streamflow time series in order to characterize hydrological droughts during the 1961-2006 period. The SRI quantifies the number of standard deviations that the monthly streamflow on a given time scale deviates from the average value of a location during a particular period. It identifies extreme wet/dry (SRI>=2.0 / SRI<=-2.0), severe wet/dry (1.5<=SRI<2.0 / -2.0<SRI<=-1.5), and moderate wet/dry (1.0<=SRI<1.5 / -1.5<SRI<=-1.0) conditions. Opposite behaviors were found in the Patagonia and Cuyo basins regarding the main drought characteristics (number of droughts, mean duration and mean severity). A large number of streamflow drought events were recorded in the Patagonian basins, with short duration and higher severity in comparison with Cuyo basins. This pattern is also observed in the long-term trends, with significant increases ?i.e. trends towards wet conditions- in the Cuyo SRI time series and decreases ?i.e. trends towards dry conditions- in the Patagonia time series. The second methodology was based on a daily threshold level for the streamflow equaled or exceeded the 70% (Q70), 80% (Q80) and 90% (Q90) of the time. Based on the difference between the observed streamflow and the threshold, we calculated statistical indicators of low flows e.g the annual number of days with low flows and the annual and seasonal streamflow deficits. These statistics indicate the presence of inter-annual and inter-decadal fluctuations, which differ from Cuyo and Patagonian basins and agrees with the observed patterns based on the SRI. Seasonal deficiencies