Abstract
New York City (NYC) is an ultra-urban region, with over 50% impervious cover and buried stream channels. Traditional flood studies rely on the presence of stream gages to detect flood stage and discharge, but these methods cannot be used in ultra-urban areas. Here we create a high-resolution radar rainfall dataset for NYC and utilize citizen and expert reports of flooding throughout the city to study flash flooding in NYC. Results indicate that interactions between the urban area and land–sea boundary have an important impact on the spatial variability of both heavy rainfall and flooding, sometimes in contrast to results obtained for other cities. Top days of daily and hourly rainfall exhibit a rainfall maximum over the city center and an extended region of higher rainfall downwind of the city. The mechanism for flooding appears to vary across the city, with high groundwater tables influencing more coastal areas and high rain rates or large rain volumes influencing more inland areas. There is also a strong relationship between sewer type and flood frequency, with fewer floods observed in combined sewer areas. Flooding is driven by maximum one-hour to one-day rainfall, which is often substantially less rain than observed for the city-wide daily maximum.
Highlights
Flash flooding is a costly and deadly problem throughout the United States
A 15-year (2001–2015) high-resolution (1 km2, 15 min) radar rainfall dataset was created for the warm season (April–September) in the New York City metropolitan area
Hydro-NEXRAD-processed radar-rainfall fields were bias-corrected on a daily basis to create the dataset
Summary
Flash flooding is a costly and deadly problem throughout the United States. In 2015, flash flooding caused more fatalities and cost more dollars in damages than any other weather-related hazard [1]. Flash flooding is often predicted using a rainfall guide: the volume of rainfall which will cause flooding in a catchment based on the volume of water which can be held in the soil at the time. This procedure is less accurate in urban areas where soil properties are less important, and rainfall intensity, not volume, drives flooding [16]. In ultra-urban areas like New York City, flash floods are difficult to detect. We create a high-resolution radar rainfall dataset for ultra-urban New York City. The paper is structured as follows: Section 2 provides a background of studies relevant to this work, Section 3 describes the data and methods used in this study, Section 4 describes results from this study, and Section 5 details the conclusions reached
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