Reuters is now reporting the following:

A major insurance company is accusing dozens of localities in Illinois of failing to prepare for severe rains and flooding in lawsuits that are the first in what could be a wave of litigation over who should be liable for the possible costs of climate change.

Farmers Insurance filed nine class actions last month against nearly 200 communities in the Chicago area. It is arguing that local governments should have known rising global temperatures would lead to heavier rains and did not do enough to fortify their sewers and stormwater drains ...

Flooding struck Illinois in April 2013, and the federal government paid more than 64,000 Illinois households and individuals more than $218 million in aid and low-interest loans following the storms, said the state's Emergency Management Agency.

This should make for an interesting suite of lawsuits, since they all hinge on proving anthropogenic global warming in an American court of law, and then directly downscaling any such human-induced changes to the Chicago area.  Good luck.

Apparently "lawyers for the localities will argue government immunity protects them from prosecution."  Perhaps a good first blocking move, but even a cursory look at the historical climate and weather data for the Chicago area illustrates how difficult proving this case should be.  Ideally, the local communities will fight back a little harder if the immunity defense doesn't work.

There has been no significant trend in annual temperatures for the Chicago area since 1970, or since the start of the period the recent National Climate Assessment tells us we should be seeing the most prominent anthropogenic climate change impacts.  No trend since 1990, either.

There is most certainly no trend in annual precipitation for the Chicago area since 1970 (or 1990).

April 2013 was the wettest April in the Chicago area's history, dating back to the start of records in 1871, but at 8.68 inches it was only 4 percent higher than the previous record of 8.33 inches.  There is no significant trend in April precipitation since 1970 (or 1990).  Indeed, the correlation is negative (i.e., toward less precipitation during this month, not more).

On April 18, Chicago received 3.54 inches of rain.  But this isn't even a daily record for the month of April.  Coincidentally, back on April 18, 1975, the city received even more rain: 3.83 inches.  There hasn't been a statistically significant trend in maximum one-day rainfall during April for Chicago since records begin in 1871.  In fact, since 1970 the correlation has been negative (i.e., toward fewer one-day rainfall maxima in April, not more).

The maximum one-day precipitation in each calendar year also hasn't shown any trend since 1970 for the Windy City area.

Overall, it seems like a very hard scientific sell to provide conclusive evidence that anthropogenic climate change was in any way behind Chicago's floods in April 2013.  The data just doesn't support this conclusion.