The current year is full of unexpected weather and climate phenomena. We have already observed record high temperatures, heat and rain waves , widespread fires and floods. One example of the latter was the flooding in New York. What caused it? Were weather factors or the city’s infrastructure at fault, or perhaps too rapid a climate change that we, as humanity, cannot cope with?
What is a flash flood?
We wrote about flash floods as a sign of a changing climate and how to protect against them in one of our previous articles “Flashfloods – how to protect yourself from the elements.” Flash flooding occurs when a small area receives intense rainfall in a short period of time. This phenomenon is usually triggered by violent, heavy rainfall caused by local cloud bursts or slow-moving and stationary storm cells. The risk of flooding is raised by the high level of urbanization and the high proportion of impervious surfaces in cities. These are the main factors that triggered, among others. New York flooding. Therefore, it is important to adapt the infrastructure of cities, as we wrote about in the article “Flash floods – an increasing concern for local governments.”
Occurrence of flash floods in New York City
The flooding in New York City began on the morning of September 29, 2023, when a massive downpour passed over the city. The storm was a remnant of tropical storm Ophelia. New York State Governor Kathy Hochul declared a state of emergency for the city and surrounding counties, including Long Island and the Hudson Valley. She also stressed the dangers that could result from traveling on the roads during the floods. The dangers and the need for caution were also communicated by New York City Mayor Eric Adams. Downpours also affected other cities in the northeastern part of the US, including Boston, Philadelphia and southern Connecticut, but the worst effect of the rainfall was flooding in New York City. Fortunately, sunny weather returned to the city after the torrential downpours that lasted all day Friday, thanks to the high winds.
Flooding in New York – how much rainfall was there?
In 3 hours, as much rain fell in New York as is usually recorded in a month at this time of year. The amount of rainfall per hour reached 2.5-5 cm, and the total amount of rainfall at points was more than 200 l/m2. A total of more than 22 cm of rain fell in some areas of Brooklyn and at JFK Airport. The 1963 record for daily and hourly rainfall in the city was broken. The flooding in New York was inevitable. In addition, moderate rains fell in the city throughout the week. It was the second such wet September in New York’s history – the previous record dates back 140 years ago!
Effects of the floods
Flooding in New York has left the city paralyzed. Basements, sewers and streets in the boroughs were flooded: Brooklyn, Manhattan, Queens, as well as in New Jersey. Pedestrians were wading up to their knees in water, abandoned their cars in the streets, and the subway was waterlogged, resulting in the suspension of operation of some lines and the closure of some stations. LaGuardia Airport’s terminal was temporarily closed, and many flights were delayed or canceled. At the Central Park Zoo, a sea lion swam outside the fence, sports games were postponed, students at some schools were dismissed from classes, and patients were evacuated from the hospital. The flooding in New York City required the help of National Guard soldiers. In some areas of the city, emergency services had to assist evacuations, but ultimately there were no fatalities.
Causes of flash flooding in New York City
Why was the downpour catastrophic in its effects? New York, like most major metropolises, is covered mostly with concrete. Heavy precipitation is not absorbed by the ground, but is discharged through storm drains. Such coping even with heavy rains usually passes the test, but the problem arises when the heavy downpour is also of high intensity. Water quickly fills the available pipes, and excess water accumulates on the surface. In addition, the pressure in the sewer system increases, which can lead to sewage knocking out and pipes leaking. The flooding in New York City was compounded by the fact that drains were often blocked by trash and debris washed in from the streets, preventing water from draining. Rainfall in the week preceding the flood also contributed to the city’s flooding, causing the ground to become saturated with water.
Sewer infrastructure in New York City
According to the commissioner for the European Union. New York City’s environmental protection officer, Rohit Aggarwali, the rainfall discharge capacity of the city’s sewer system is ca. 4.5 cm per hour. During the described downpour, at its peak, more than 6 cm of rainfall per hour was recorded. According to the authorities, New York City was designed for the amount of rainfall of the past, when sewers could handle even heavy storms. Hurricanes and massive downpours haunting the U.S., including New York City, over the past 15 years have been characterized by much heavier rainfall and flooding in the city. According to experts, such weather events are the result of the evolution of the climate, which is changing faster than the city can modernize its infrastructure. Another flood in New York is therefore a real threat, requiring sewer reconstruction as soon as possible.
New York – plans to prevent future floods
Daniel Zarrilli, a Columbia University climate advisor and former mayoral advisor on climate issues. climate policy, believes that rebuilding New York City’s sewer infrastructure will require a great deal of creativity and investment. The current sewer system covers more than 12,000. km of pipes carrying both wastewater and rainwater to treatment plants, rivers and lakes. City authorities estimate that the infrastructure overhaul will take decades and cost $100 billion. In the meantime, the city is working on creating alternatives to the sewer system – building retention basins and increasing the amount of green space that can absorb excess water and prevent the effects of events such as the next flood in New York. Also under consideration is the reconstruction of streets to temporarily and safely store excess water, and the installation of more pumps to help drain water from the sewer system.