In this post i want to introduce you to the so called Pacific Decadal Oscillation, or PDO for short. Just to give a short introduction to this huge (and complex) subject, the text below follows straight from Wikipedia.
...The PDO is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. ...
We already know that the Pacific Ocean is a pretty big place, so this kind of phenomena should be correlated with climate-dependent variables. To show this, i looked at a 120 months moving average of both the PDO and the Affluent Natural Energy (ANE for short) generated in the Brazilian southeast region. The ANE represents the energy that can be generated from the water that flows to the damns.
Due to it's climate and continental dimension, the Brazilian electricity generation system is characterized by the strong predominance of Hydroelectric generation (about 80% of the installed capacity). The code below plots the data from Jan-1931 to Nov-2012, and we see a strong correlation, despite the fact that the Pacific north of 20° N is far away from the Brazilian coastline.