Answer: The heavy precipitation indicator shows the frequency of heavy single-day rain or snow events over a year. These events exceed the normal frequency of heavy precipitation. Here we include two different scenarios that are considered heavy precipitation—greater than 0.5 inches and 1 inch over a 24-hour period. Since precipitation varies by area, we show two locations representing both states surrounding the Long Island Sound—La Guardia Airport in Queens and Igor I. Sikorsky Memorial Airport in Bridgeport, CT.
Heavy precipitation can have severe implications on the overall ecosystem health of the Long Island Sound. Rainfall on impervious surfaces increases the runoff input to waterbodies. Runoff carries a multitude of pollutants, including various nutrients (nitrogen), bacteria (E.coli), emerging (PBDE, pharmaceuticals) and legacy (heavy metals, PCBs) contaminants, and debris. The increase in pollutants impairs water quality, reduces habitat quality, and harms biota in the Sound. Furthermore, high nitrogen concentrations in the water column creates hypoxic conditions, meaning the increase in nutrients stimulates algal growth (known as algal blooms), and leads to severe decreases in dissolved oxygen. This depletion in oxygen induces massive fish kills. These impacts can scale-up and inhibit key ecosystem services that residents of the watershed rely on. For example, higher intensity and frequency of precipitation can result in flooding, which can enhance coastal erosion, hinder agriculture production, and damage coastal infrastructure.
Both Connecticut and New York Health Departments implement policies to restrict swimming and other recreational activities after rainfall exceeds a certain amount over a specific period of time. Connecticut prohibits swimming if rainfall exceeds 1 inch over a 24-hour period, or over 2 inches within 48 hours. In New York, Suffolk County also restricts swimming when rainfall exceeds 1 inch over a 24-hour period, while it’s 0.5 inches for Nassau County (New York City issues a rain advisory when rainfall exceeds 0.3 – 2.5 inches and Westchester issues after 0.5 – 2.0 inches). The increase in precipitation induces bacteria outbreaks in the waterbody and therefore forces beach closures to protect the public from adverse effects. Furthermore, impaired water quality can also impact the commercial and recreational fisheries. When fish and shellfish consume these contaminants, it can cascade through the food chain and pose serious health effects on human – this is called biomagnification.
Both New York and Connecticut locations are experiencing the same trend—increase in frequency of heavy precipitation events. Both scenarios, greater than 0.5 inches and 1 inch, are increasing in both Connecticut (18 and 24 percent increase, respectively) and New York (12 and 19 percent increase, respectively). We chose to use the 0.50 inches scenario as the New England region has seen a significant increase in the amount of precipitation above this threshold compared to other regions of the country.
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