| Summary: | The interannual variability of precipitation and river flow in the area of Comahue and northern Patagonia in Argentina is analyzed in this chapter. Both the monthly and annual precipitation and the mean annual flow data over the period 1985-2012 have been used to perform this study. For each station, the 25th and 75th percentiles of precipitation and flow were used to classify each year as dry (precipitation or flow less than 25th percentile), wet (greater than 75th percentile) or normal. Finally the years were classified as dry, wet or normal if the greater number of stations with in each basin belongs to that category. Some parameters were defined and calculated in order to assess the intensity and the spatial coverage of all the extreme (wet and dry) events. Thus, all the extreme events are revealed in the different basins and their severity and affected areas in each case were documented. Finally, the presence of significant climate forcing associated with extreme precipitation detected above was investigated. As the maximum signal was in spring, climate forcing in this season was analyzed in detail. Results indicate that the positive phase (negative) of the Indian Ocean Dipole, El Niño Modoki and the El Niño-Southern Oscillation is associated with the highest positive (negative) precipitation anomalies in spring in the Comahue region. Positive(negative) precipitation anomalies are also associated with the negative (positive) phases of the Antarctic Oscillation, the South Atlantic Ocean Dipole and the Multidecadal Atlantic Oscillation and with the weakening and eastward shift of the Pacific High and the intensification and shift to the south of the Atlantic High. © 2017 Nova Science Publishers, Inc.
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