Detailed Flood Modeling and Hazard Assessment from Storm Tides, Rainfall and Sea Level Rise

Abstract:

A flood hazard assessment has been conducted for the Hudson River from New York City to Troy at the head of tide, using a three-dimensional hydrodynamic model and merging hydrologic inputs and storm tides from tropical and extra-tropical cyclones, as well as spring freshet floods. Our recent work showed that neglecting freshwater flows leads to underestimation of peak water levels at up-river sites and neglecting stratification (typical with two-dimensional modeling) leads to underestimation all along the Hudson. The hazard assessment framework utilizes a representative climatology of over 1000 synthetic tropical cyclones (TCs) derived from a statistical-stochastic TC model, and historical extra-tropical cyclones and freshets from 1950-present. Hydrodynamic modeling is applied with seasonal variations in mean sea level and ocean and estuary stratification. The model is the Stevens ECOM model and is separately used for operational ocean forecasts on the NYHOPS domain (http://stevens.edu/NYHOPS). For the synthetic TCs, an Artificial Neural Network/ Bayesian multivariate approach is used for rainfall-driven freshwater inputs to the Hudson, translating the TC attributes (e.g. track, SST, wind speed) directly into tributary stream flows (see separate presentation by Cioffi for details). Rainfall intensity has been rising in recent decades in this region, and here we will also examine the sensitivity of Hudson flooding to future climate warming-driven increases in storm precipitation. The hazard assessment is being repeated for several values of sea level, as projected for future decades by the New York City Panel on Climate Change. Recent studies have given widely varying estimates of the present-day 100-year flood at New York City, from 2.0 m to 3.5 m, and special emphasis will be placed on quantifying our study’s uncertainty.