U.S. Rep. David Cicilline: Precipitation in Rhode Island has risen by just over a foot in 100 years

People who warn that humanity is dramatically changing Earth's climate invoke several indicators to prove their point. They note the rise in sea levels, the increase in global temperature and the growing acidification of the oceans.

In a May 1, 2015, commentary in The Providence Journal, U.S. Rep. David Cicilline, a Rhode Island Democrat, along with Michael Shank, director of media strategy for Climate Nexus, a group devoted to warning about climate change, invoked those warning signs, and more.

"Global warming is happening, here and now. Its impact is already being felt in coastal states like Rhode Island, and greenhouse gas emissions are undeniably responsible," they said.

Cicilline and Shank argued that, "Greater annual precipitation, which has increased in Rhode Island by over 12 inches in the last century, also means movement and mixing of pollutants, nutrients, contaminants and salinity levels, all of which can critically undermine marine productivity."

We know we've seen some wet years recently, but we also know how variable weather can be from year to year. So the statistic in that paragraph made us wonder -- has precipitation in the state actually increased by more than a foot over the past 100 years?

When we contacted Cicilline's office to ask for the source of the claim, spokeswoman Alex Macfarlane directed us to two publications.

The first is a four page fact sheet from the University of Rhode Island's Sea Grant program which says, "In Rhode Island, precipitation has increased by over 12 inches since 1905, mostly during non-summer months." Because the undated sheet refers to a weather event in 2012, it's clear that the "over 12 inches" is referring to a time span of at least 107 years.

The second piece of evidence was from a 2008 book, "Science for Ecosystem-Based Management: Narragansett Bay in the 21st Century." In the second chapter, Michael Pilson of URI's Graduate School of Oceanography reports that annual precipitation data from Providence and Warwick from 1905 to 2006 show an increase of 13 inches. That's over 102 years.

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So Cicilline was citing a good source, although the data are eight years old.

To determine if the trend is true today -- and the congressman made it sound like he was talking about current precipitation numbers -- we downloaded the National Weather Service data through 2014. Rainfall and melted snow totals can vary dramatically year to year, so we used Microsoft Excel to calculate a trend line using the last 100 years, beginning in 1914.

The increase: 11.9 inches.

And if you take the data back to 1905, a longer time than Cicilline was citing, the increase is 13.5 inches. The trend line (not the actual precipitation amounts) goes from 36.3 inches in 1905 to 49.8 inches in 2014.

That's a 31 percent increase in precipitation in the past century; 37 percent since 1905.

The months that have seen the greatest precipitation increases are March, October and November. The only month with a decrease has been July, and it's been slight.

In summary, David Cicilline said annual precipitation "has increased in Rhode Island by over 12 inches in the last century." Reliable but slightly out-of-date sources back him up. The 100-year increase we calculated going through 2014 is just a tenth of an inch shy of 12 inches, but the difference between that and being slightly over 12 inches is just a few drops in the bucket.

Thus, we rate the claim as True.

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