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    Is Your Stormwater System Prepared for a 100-Year Storm?

    by Erin Zaske, Chief Development Officer

    Every second, the NYC Climate Clock strikes another second down, stormwater systems face greater and greater threats. One threat is the 100-year storm.

    A 100-year storm is a massive storm that historically had a 1% chance of occurring every year. However, this name may not be as suiting as it once was. As the atmosphere warms, the air's ability to hold moisture increases. When the moisture is eventually released in storm events, the quantity of rain is much higher in warmer air than in cooler counterparts. These massive storms are commonly referred to as extreme rain events, with some large enough to be categorized as infamous 100-year storms. States on the West Coast of the US braced for extreme rain events 51% more often in 2017 than in 1950. In the northeast, these events occurred 85% more frequently [1]. Ning Lin, an associate professor of civil and environmental engineering at Princeton, warns that 100-year floods caused by these storms may become "one-year floods" in the north [2]. These extreme rains and the flooding, landslides, and other catastrophes they cause, are considered one of the deadliest and most damaging weather events worldwide [3]. In 2017, rain alone caused upwards of $145 billion in damages [4]. While some areas are more prone to extreme rain events, the EPA predicts a national 100-year flood increase of 45% by 2100 [5].

    What dangers are there for aging infrastructure?

    Infrastructure constructed to withstand 100-year storms based on mid-20th century data now face storms that exceed their runoff management capacity up to 2.5 times [1]. These more intense and frequent storms wear down systems faster, increase strain, and in many cases leave older systems overwhelmed by increasingly common extreme weather events. As climate change and historical data become less predictive of future events, it is becoming increasingly challenging to predict flow and storage capacity.

    What action can we take?

    While expanding stormwater system capability is a large investment, this might be required in some high-risk regions in the future. Retrofitting and implementing green infrastructure into your stormwater systems may be a more cost-effective approach. Green infrastructure can absorb stormwater by mimicking the site's natural hydrology through porous surfaces, allowing for onsite holding and treatment of stormwater. With or without stormwater system retrofits, routine preventative maintenance is required to ensure systems remain functioning and protecting your property. Maintaining new systems reduces their wear and tear, limits failures, and mitigates NOVs. For older systems, maintenance can ensure your systems are capable of handling their maximum capacity during storm events.

    To learn how to prepare your stormwater system in the days before an extreme rain event, click here.


    [1] "Not your father's 100-year storms," Stormwater Report, 2019.
    [2] P. University, "'100-year' floods will happen every 1 to 30 years, according to new flood maps," Phys, 2019.
    [3] A. Witze, "Why extreme rains are gaining strength as the climate warms," Nature, 2018.
    [4] P. Wright, "Heavy Rainfall Has Increased by Up to 70 Percent in Parts of the U.S. Since the 1950s, and It Will Only Get Worse, Experts Say," The Weather Channel, 2018.
    [5] "Mange Flood Risk," United States Environmental Protection Agency. [Online].