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SNAPSHOT: Storms and NYC Watershed

Heavy precipitation can impact water storage areas, such as reservoirs and watersheds, by causing flooding and water quality issues. Therefore, identifying which storm types are most likely to cause heavy precipitation or streamflow events allows water managers to prepare and protect water supply systems.

A study published by the American Meteorological Society’s Journal of Hydrometeorology analyzed how storms impact the Ashokan Reservoir, which supplies 40 percent of New York City’s drinking water. The research was led by Ph.D. candidate Katherine L. Towey (The Graduate Center, CUNY). Her collaborators included Professor James Booth (The City College of New York, The Graduate Center) and Professor Allan Frei (Hunter College, The Graduate Center).

A storm cloud looms over lower Manhattan

Researchers parsed through data from 1950 to 2012 to identify the 100 heaviest one-day precipitation, multiday precipitation, and streamflow events. The results showed that approximately 43 percent of the top 100 events fell into all three categories. The heaviest one-day precipitation and multiday precipitation events occurred most often during hurricane season, which is between June and November. Half of the top 100 one-day streamflow events occurred in March, April, and May, and likely involved snowmelt.

Specifically, extratropical cyclones were associated with at least 70 percent of the top 100 precipitation and streamflow events, whereas tropical cyclones accounted for 20 percent of the top 100 one-day precipitation events and less than 10 percent of the top 100 one-day streamflow events.

SNAPSHOT is SUM’s afternoon science brief.