Extreme Hourly Precipitation Risk for New York City Post-Ida
The remnants of Hurricane Ida caused major damage and death in the United States on September 1st, 2021, and 11 people drowned in flooded basement apartments within New York City (NYC). It was catastrophic because the maximum hourly precipitation intensity, recorded as 3.47 inches (88.1 mm) at Central Park, was unprecedentedly high for the NYC region. The stormwater infrastructure in NYC is built for 1.75 inches (44.5 mm) per hour, and so understanding the dynamic risk associated with Ida can inform city planning efforts for climate change’s impact on short duration extreme precipitation events. We contextualize this storm’s record-breaking hourly intensity within the historical record and project its risk in the near- to medium-term future using nonstationary models conditioned on six future Cooling Degree Day projections from three climate models as a covariate, each with a SSP126 and SSP370 scenario. The likelihood of such a storm was increasing even before Ida happened, and the highest projected risk accumulated over the next 50 years (2024-2073) reaches an expected number of future Ida-like events of 1.14, which is 52 times larger than the risk under the stationary risk model.