170,000 evacuated by unprecedented floods in Argentina, Brazil, Paraguay, and Uruguay.

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3. It's also a study in contrasts as far as public works.

In Paraguay, where the river crested at 7.82 meters (26 feet), there are 200,000 evacuees. http://www.laprensagrafica.com/2014/06/27/paraguay-200000-evacuados-por-inundaciones

In Argentina, where the river crested at 15.86 meters (52 feet), there are 20,000 evacuees.

The potential affected population was similar in both countries. And both countries have extensive, low-lying shores along the Paraná, Paraguay, and Uruguay rivers; but whereas levees and drainage systems protect most of those communities on the Argentine side, Paraguay for the most part lacks these - even along the capital, Asunción.

It would have been even worse in Paraguay had it not been for Itaipú and Yacyretá dams - built by Brazil and Argentina, respectively, and two of the largest in the world.

The key to prevent future tragedies of this scale, given that climate change will probably make torrential rains more common, is effective zoning laws (banning people from building too close to certain river shores) and, above all, public works.

That's what FDR understood, and today there are 50 million people or more in the U.S. (mainly in the South) who are reasonably safe from catastrophic flooding thanks to him.