El Niño Southern Oscillation (ENSO)-induced hydrological anomalies in central Chile

Abstract

Abstract. The El Niño Southern Oscillation (ENSO) is a major driver of climatic anomalies around the globe. How these climatic anomalies translate into hydrological anomalies is important for water resources management, but difficult to predict due to the non-linear relationship between precipitation and river discharge, and contrasts in hydrological response in regions with different hydrological regimes. In this study we investigate how ENSO-induced climatic anomalies translate into hydrological anomalies by focussing on Central Chile (29–42° S), a relatively small area affected by ENSO, that displays steep latitudinal and elevational climatic gradients. We analyse daily discharge timeseries from 178 discharge stations together with monthly temperature and precipitation data. Based on the Multivariate ENSO Index (MEI) we classified the discharge data for the time period 1961–2009 into El Niño (MEI>0.5), La Niña (MEI<-0.5) and non-ENSO periods (˗0.5>MEI<0.5), and calculated relative differences in mean monthly temperature, precipitation, and discharge, as compared to non-ENSO conditions. The results reveal that precipitation and specific discharge generally increase during El Niño events, while they decrease during La Niña events. However, there exist large spatial and seasonal variations. The mean monthly precipitation and specific discharge anomalies during both the El Niño and the La Niña phases are strongest in the semi-arid region (29-32° S), followed by the mediterranean (32°–36° S) and humid-temperate (36°–42° S) regions. During El Niño events, the semi-arid and mediterranean regions experience mean monthly specific discharge increases of up to +396.5 % and +104.5 %, respectively, and a considerable increase in the frequency and magnitude of high flows. In contrast, discharge in the humid-temperate region is most sensitive to rainfall deficits during La Niña events, as revealed by an increased frequency of low flows. We find that the different hydrological regimes (rainfall- or snow-dominated) show large contrasts in how ENSO-induced climatic anomalies are translated into hydrological anomalies, in that snowmelt induces a delayed discharge peak during El Niño, provides a minimum streamflow during dry La Niña conditions, and reduces the discharge variability in rivers. Finally, we discuss the implications for water resources management, highlighting the need for different ENSO prediction and mitigation strategies in central Chile, according to catchment hydrological regime.