Local floods reflect rise in extreme rainfall, experts say

UTICA -- Just two days before Halloween, Utica Mayor Robert Palmieri was at the scene of a creek cleanup in North Utica.

While an excavator worked to clear the creek bed, Palmieri discussed the city's efforts to mitigate flooding by clearing debris and working with private entities such as Riverside Center. He also mentioned another culprit for recent flooding events.

"I know no one wants to talk about climate change," Palmieri said. " ... But the rainstorms that we're having at this point, where we used to get them once every maybe five years, we're getting them once every two years, sometimes twice a year."

Two days after his visit, hard rains and buffeting winds in the Mohawk Valley caused widespread flooding. Homes and businesses were damaged, while creeks overflowed their banks.

The highest recorded rainfalls in Oneida County were in Sauquoit, with 4.2 inches, and Woodgate, 3.5 inches, according to the National Weather Service.

These significant rainfall events with more than 2 inches of precipitation are becoming more common regionally and locally, said climatologist Jessica Spaccio with the Northeast Regional Climate Center at Cornell University.

Data collected by the climate center shows an increase in the frequency of heavy rain events, as well as an increase in the amount of rain during each event.

The 2014 National Climate Assessment found a 71 percent increase in total precipitation during the heaviest 1 percent of precipitation events from 1958 to 2012 in the Northeast.

The increase in precipitation intensity is being observed locally as well. Data provided by the climate center shows the highest annual precipitation event is trending upward at weather stations at the former Oneida County Airport and in Boonville.

The average highest annual precipitation event at the airport increased from 2.1 inches to 2.4 inches between 1952 and 2006. In Boonville, the average rose from 2.2 inches to 3.1 inches from 1949 to 2019.

The Boonville data showed three of the five highest single-day rainfall events were in the past 20 years, including a 6.4-inch peak in 2010.

The number of days with more than 2 inches of rain has also trended upward at the same recording stations in the same time span. Boonville saw an increase from about one day a year to twice a year, while the airport saw a bump from an average of once every two years, to 1.4 days per year.

In the last seven years of data for the airport, six years saw at least two days with more than two inches of precipitation. There were only six such years in the previous 47 years of data, according to the Northeast Regional Climate Center at Cornell University.

Heavy rainfall, historic flooding

To understand how extreme precipitation can be, scientists and municipalities use tables that categorize the event based on inches of precipitation over a set time span. The extreme precipitation table for Utica, generated by the climate center at Cornell, defines a 100-year event as 5.77 inches of precipitation in a 24-hour span.

A 100-year precipitation event in an hour span would be 2.48 inches based on the same table.

Spaccio said the designations are based on probability. So a 100-year precipitation event has a 1% chance of happening in any given year, based on historical data.

As a result, an area could theoretically have two 100-year precipitation events in back-to-back years.

On Halloween, the weather service recorded 2.92 inches of rain in Utica over a 24-hour span. Based upon the rainfall total, the storm could be defined as a five-year precipitation event.

As a historical comparison, the July 1, 2017, storm, which also caused widespread regional flooding, dumped 4 inches of rain on Utica in 48 hours. The intersection of Noyes Street and Lincoln Avenue and the North-South Arterial were among the areas heavily impacted by floodwaters from the storm.

The July 2017 storm would be defined as a 10-year event under the climate center's extreme precipitation table for Utica.

Both precipitation events triggered flooding throughout the region -- and the Sauquoit Creek in Whitesboro was heavily affected in each instance.

Early on Halloween, the U.S. Geologic Survey recorded a discharge of less than 100 cubic feet per second from Sauquoit Creek. Just before midnight, the discharge was measured at 5,730 cubic feet per second.

It was the second-highest recorded peak discharge rate recorded in over five years at the site, trailing only the 5,820 cubic feet per second on July 1, 2017.

The federal government determines flood classification on probability similar to precipitation events. So, a 100-year flood event is a peak flow in a stream that has a 1 percent chance of occurring, measured in cubic feet per second.

A 10-year flood event at Sauquoit Creek in Whitesboro would be a peak discharge of 5,873 cubic feet per second, according to a Federal Emergency Management Agency flood insurance study in 2013. A 100-year flood event would have a peak discharge of 10,222 cubic feet per second at the same location.

Mike Mahoney, Utica's city engineer, said the city's infrastructure was traditionally built for a 10-year event, as preparing for a 50- or 100-year event would require massive, expensive infrastructure.

Most communities design stormwater systems around 5- to 20-year events, according to FEMA.

More than just rain

The region is going through a particularly wet period, said David Nicosia, a warning coordination meteorologist for the weather service in Binghamton. Even within the trend of more extreme rainfall events, it's possible the weather could dry out, he said.

"Climate is long-term," Nicosia said.

Nicosia was also cautious to draw any direct lines between climate change and heavy rain events, though he cited the National Climate Assessment finding of more precipitation in those events from 1958 to 2012.

Other factors besides heavy rains, including infrastructure and development, may contribute to flooding in Oneida County.

In January, Gov. Andrew Cuomo sent a letter to CSX about the railroad bridge in Whitesboro at Sauquoit Creek, due to concerns it traps debris which causes flooding. In a February story in the Observer-Dispatch, Whitesboro Mayor Bob Friedlander cited development in New Hartford as a possible source of more significant flooding.

Palmieri said the city has sent a letter to the state Sept. 13 requesting to participate in Resilient NY during an Oct. 29 interview. The state program funds flood mitigation studies along flood-prone streams and identifies important projects aimed at alleviating the risk.

"That's what this watershed study is going to provide at this point -- all these different details that this engineering firm (is) going to be able to say, 'What is going to be our best process moving forward? How can the state help us with the infrastructure? Is it infrastructure, is it maintenance, is it a combination of both,'" Palmieri said.

Contact reporter Steve Howe at 315-792-5015 or follow him on Twitter (@OD_Howe).

___

(c)2019 Observer-Dispatch, Utica, N.Y.

Visit Observer-Dispatch, Utica, N.Y. at www.uticaod.com

Distributed by Tribune Content Agency, LLC.