Background
The authors write that river streamflows "are excellent climatic indicators," especially in the case of rivers "with continental scale basins" that "smooth out local variations" and can thus "be particularly useful to study global forcing mechanisms."

What was done
Focusing on South America's Parana River -- the world's fifth largest in terms of drainage area and its fourth largest with respect to streamflow -- Mauas et al. analyzed streamflow data, collected continuously on a daily basis since 1904, for both trends and periodicities.

What was learned
With respect to trends, the three researchers report that "the flow of the Parana is larger in the last three decades, with a mean value almost 20% larger than that of the first 70 years of the 20th century." Even more importantly, they say that "the stream flow during the last 30 years has increased in the months in which the flow is minimum [our italics], while the flow remains more or less constant during the months of maximum," noting that "the same trend is also found in other rivers of the region."

With respect to periodicities, they report that the detrended time series of the streamflow data are correlated with the detrended times series of both sunspot number and total solar irradiance, with Pearson's correlation coefficients between streamflow and the two solar parameters of 0.78 and 0.69, respectively, at "a significance level higher than 99.99% in both cases."

What it means
Whereas climate alarmists contend that both droughts and floods should increase in response to global warming, the Parana River data give no hint of enhanced maximum streamflow (which could lead to flooding) over the entire course of the 20th century, when climate alarmists claim the planet experienced a warming that was unprecedented over the past two millennia. And in an even stronger refutation of the two-pronged climate-alarmist claim, the Parana River data reveal a large increase in minimum streamflow, indicative of a tendency for less drought to occur, which is just the opposite of what they predict for this phenomenon. Last of all, whereas climate alarmists are loathe to acknowledge any significant impact of solar activity on climate, Mauas et al. find it to be incredibly significant with respect to the hydrologic climate of the Parana River basin, in harmony with what has also been found to be the case for the hydrologic climates of the basins of other South American rivers.