Patterns of spatial and temporal variability in streamflow records in south central Chile in the period 1952-2003

In this work we study the time series of annual and seasonal streamflow for 44 rivers in southern Chile, spanning the ecoregion between 34 S and 45 S for the 1952-2003 period. We analyze spatial variability using a clustering process to define regional streamflow averages. We find two main regions, divided approximately by parallel 37.5 degrees S. The analysis includes application of the multitaper (MTM) and maximum entropy (MEM) methods to find periodicities or interannual and decadal cycles. Singular spectral analysis (SSA) is applied in order to augment the signal-to-noise ratio. Significant correlation with climatic indexes was found at different spatial and temporal scales, with El Nino-Southern Oscillation (ENSO) influence being stronger at the northern subregion, and notably the Antarctic Oscillation (AAO) and the Pacific Decadal Oscillation (PDO) showing strong correlation with summer flows in the southern subregion. Also, we found significant decreasing trends affecting a region between 37.5 degrees S and 40 S. These are coherent with decreasing trends observed in precipitation in the area, and also with a decreasing trend observed in the Southern Oscillation Index (SOI). These findings provide, for the first time, a comprehensive view of the streamflow variability in a sensitive ecoregion in South America. We expect that these results will inform decision making in a context of increasing water demands for diverse uses as well as contribute to the general understanding of climatic patterns of variability in the Pacific Rim.