Inter-annual variability of the Cuyo rivers' streamflow in the Argentinean Andean mountains and ENSO events

Abstract

The main source of the Cuyo rivers' water volume is the melting of winter accumulated snow over the Andes subtropical high mountains. Particularly between 30 and 40°S, Andean winter precipitation (April–September) shows both spatial coherence and significant correlations with the Santiago precipitation. That is why this zone, which corresponds to the Cuyo rivers' basin areas, is homogeneous with respect to the streamflow's inter-annual variability. The streamflows of the rivers in this region are highly correlated to each other. Therefore, the Mendoza river, which is one of the Cuyo rivers is taken as reference for all these rivers to study the summer streamflow inter-annual variability (October–March) and the association with ENSO events. This river exhibits behaviour associated with equatorial Pacific Ocean anomalies. Above average streamflow is more likely to occur during a mature phase of El Nino event in the southern summer. This implies abundant and frequent snowfalls during the previous winter over the high subtropical Andes. Abundant and frequent snowfalls in the winter after an El Nino year, and the subsequent high flows during the following summer, are less likely to occur. This teleconnectivity is not absolute since some warm events were recorded and simultaneous flows remained below average. Instead, values under the mean flow are more likely during cold event years, with exceptions being quite rare. This atmospheric circulation study involves principal component analysis of daily surface pressure fields from 1972 to 1983. It reveals identifiable characteristics for Andean winters with above average precipitations. Wet winters are charecterized by both less explained variance by the first principal component, whose pattern corresponds to a high zonal flow component, and more explained variance of those patterns matching low pressure systems and cold frontal passages which have a high meridional flow component. The inverse occurs in dry winters. Generally, patterns corresponding to post-frontal anticyclones show no significant correlation with the precipitation over the high subtropical Andes. © 1998 Royal Meteorological Society