  Recently, the study of the influence of solar activity on the Earth's climate
received strong attention, mainly due to the possibility, proposed by several
authors, that global warming is not anthropogenic, but is due to an increase in
solar activity. Although this possibility has been ruled out, there are strong
evidences that solar variability has an influence on Earth's climate, in
regional scales.
  Here we review some of these evidences, focusing in a particular aspect of
climate: atmospheric moisture and related quantities like precipitation. In
particular, we studied the influence of activity on South American
precipitations during centuries. First, we analyzed the stream flow of the
Paran\'a and other rivers of the region, and found a very strong correlation
with Sunspot Number in decadal time scales. We found a similar correlation
between Sunspot Number and tree-ring chronologies, which allows us to extend
our study to cover the last two centuries.
