Has Chicago’s annual precipitation been affected by global warming?

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Dear Tom,

Has Chicago’s annual precipitation been affected by global warming?

— John Curtis

Dear John,

Probably yes, but it is difficult to make such determinations because Chicago’s annual precipitation totals are available for 146 years (beginning with 1871), a period of time possibly too short for those kinds of considerations.

Looking first at two periods, 1871-1943 and 1944-2016 (the first and second halves of the 146-year period), average annual precipitation was 32.96 and 36.23 inches per year, respectively, for the two periods.

Looking next at periods of about 30 years (1871-99, 1900-29, 1930-59, 1960-89, 1990-2016), annual precipitation was 35.50, 32.44, 32.99, 36.72 and 37.09 inches, respectively.

From 2010-16, it has averaged 39.03 inches. It appears Chicago’s precipitation is increasing considerably, based on these calculations.