A warming climate can help explain New Haven’s intense flooding
As the climate continues to warm, severe weather events like last week’s floods may occur more frequently.
James Richardson, Contributing Reporter
Between Sept. 1 and Sept. 2, the remnants of Hurricane Ida caused heavy rainfall in Connecticut — leading to flooding and around 190 power outages in New Haven. The unexpected impact of the storm has raised questions over the increasing risks of climate change.
According to experts, a warming climate can lead to the type of heavy rainfall and flooding that hit Connecticut last week. Peter Raymond, a professor of ecosystem ecology at the Yale School of the Environment, said the prevailing data shows that severe weather events are already occurring more frequently.
“[Heavy rainfall events] are very low frequency, but they are becoming more frequent as the climate changes,” Raymond said. “It is predicted by all the models and is already showing up in our data. We have more rainfall coming in these larger events than we used to.”
According to Raymond, the warming climate can be linked to hurricanes and flooding by relatively simple science. As air temperatures warm, more water can be held in the atmosphere, causing the storms that form to also hold more water, leading to heavier rainfall.
Raymond added that as the atmosphere warms, the ocean absorbs this heat and warms as well, increasing the potential for stronger storm winds. One reason why Ida’s intensity heightened rapidly at the end of its trajectory is because the Gulf of Mexico is particularly warm.
Simon Wang, a professor of climate dynamics at Utah State University, told the News that hurricanes are a natural process that existed before recent trends of global warming. In the Atlantic Ocean particularly, Wang said, the number of hurricanes forming may not increase. But a warming climate means that hurricanes can occur with greater intensity.
According to Michael Dietz, director of the Connecticut Institute of Water Resources, scientific literature has conclusively documented the increasing intensity of weather events as the climate has warmed. Dietz pointed to a study from the National Oceanic and Atmospheric Administration comparing precipitation in the United States from the last 30 or 40 years to older data from the 1930s to the 1960s. According to Dietz, the data from the present is markedly different.
In Connecticut specifically, it used to be that a 100-year storm — a storm that has a 1 in 100 chance of happening in any given year — had a 24-hour rain total of about 7 inches. Now, recent data for the Connecticut region shows that the 100-year storm has a rain total of about 8 inches.
“That may not seem like a big change,” Dietz said. “But when you think about getting 7 inches of rain in a day, which some parts of New York City did for this hurricane, adding an extra inch on top of that saturated landscape can be devastating.”
Reports from across the nation have shown the catastrophic damage to human life and infrastructure caused by hurricanes. But even for areas that are not directly hit by a hurricane, like Connecticut, heavy flooding comes with its own share of problems.
Dietz said that an increase in storm water primarily affects the region’s combined sewer systems. A combined sewer system collects rainwater runoff, domestic sewage and industrial wastewater into one pipe. Under normal conditions, the system directs all of the material to a sewage treatment plant for treatment first before discharging it into a water body. But during heavy rainfall events, the volume of water exceeds the capacity of these treatment plants. When this occurs, there are combined sewer overflows, or CSOs, in which the untreated stormwater and wastewater are discharged directly to nearby streams, rivers and other water bodies.
There are six municipalities in Connecticut that still have CSOs, including New Haven. Data reported by CT DEEP this month shows that CSOs were triggered in New Haven in 17 different events on Sept. 1 and 2, with sewer overflows in the Mill River, the New Haven Harbor, the West River and the Quinnipiac River.
Dietz said that many Connecticut cities are trying to revamp their sewer systems and separate the stormwater from the wastewater. He said New Haven in particular has been one of the leaders in the state in implementing green stormwater infrastructure. Green stormwater infrastructure such as rain gardens can absorb the storm water into the ground and reduce the volume of water that is discharged into other bodies.
Wang said that other pieces of infrastructure in cities, such as the construction code, also need an overhaul. He said that the current infrastructure in most cities, which was built on now-outdated information, can not cope with the new intensity of severe weather events.
Raymond said that mitigation is also an important component of the response. He said that to decrease the impacts of climate change, it is necessary to decrease fossil fuel emissions.
“Ultimately, if we want this to stop, we have to stop the warming,” Raymond said.
For Wang, even before focusing on national efforts to reduce carbon emissions and rehaul infrastructure, it is important to educate people on what actions they must take during a severe weather event. He said that it is essential for people to take evacuation warnings seriously and act quickly. According to Wang, if people reacted to weather events even just 10 minutes faster, it could mean the difference between “heaven and hell.”
Wang also said the most dangerous thing for individuals to do is rely on their previous experiences with weather events when making decisions, because they have likely never experienced the kind of events that are happening now.
“Above everything, people have to be aware that they cannot be sure to be safe in a building that they believe was designed to cope with heavy rainfall,” Wang said. “Because that heavy rainfall that is going to happen tomorrow could be beyond what the building and the infrastructure can handle.”
According to the most recent report by the Intergovernmental Panel on Climate Change, the Earth had already warmed 1.1 degrees Celsius in the period of 1850-1900 and is expected to reach or exceed 1.5 degrees Celsius of warming.