Modeling and Mapping the Advance of Monthly Tidal Flooding a Possible Threshold of Inhabitability

Modeling and Mapping the Advance of Monthly Tidal Flooding A Possible Threshold of Inhabitability

Philip Orton, Stevens Institute of Technology

Collaborators: Helen Cheng, New York Sea Grant and Science and Resilience Institute at Jamaica Bay (SRIJB) Adam Parris, Brooklyn College (CUNY) and SRIJB William Solecki, Hunter College, CUNY Radley Horton, Columbia University

Primary Funding: NOAA-RISA [email protected] NOAA Sea Level Rise Viewer

[email protected] Surging Seas (Climate Central)

Motivation:

Sea level rise mappers based on daily high tide (MHHW) don’t represent the initial onset of future problems with “Sunny Day” tidal flooding à we need a better metric of tidal flooding! A single tide gauge’s “minor flood” isn’t always representative of flood risk for an entire region – New York City is a great example (at right). à We need mapping

“We need granularity as to location [of tidal flooding]” – Mark Wilbert, today What is a Useful Tidal Flood Metric?

• William Sweet’s work has revealed how nuisance flood occurrences are accelerating • Sweet and Park (Earth’s Future, 2014) referred to “tipping point” in the advancement of impacts of 30 floods per year

à Is 30 days a tipping point indicator of uninhabitability, where adaptation must occur?

[email protected] NPCC 2010, 2015, 2019 Reports

Published in the Annals of the New York Academy of Sciences

Climate Change Adaptation in New Advancing Tools and Methods Building the Knowledge Base for York City: Building a Risk for Flexible Adaptation Climate Resiliency: Management Response: Pathways and Science Policy New York City Panel on Climate Change New York City Panel on Climate Integration: Change 2010 Report 2015 Report New York City Panel on Climate Change 2019 Report NPCC Sea Level Rise Projections

Antarctic Rapid Ice Melt (ARIM) Monthly Tidal Flood Mapping with SLR: Methods Overview • Simulation – Hydrodynamic model (regional model – NYHOPS) – 35 day simulation, mean streamflows, no wind – Simulate for present-day plus all SLR scenarios • Computation – Tidal harmonic analysis - create tide-only timeseries – Compute mean of all monthly tidal maxima (MMHW) – Repeat analysis with USGS and NOAA tide gauge observations – Bias-correct modeled MMHW to observations – Bathtub mapping from estuary model to inland flood zones Observed water levels VS mean monthly and daily high water

MHHW is a standard tidal datum

MMHW is not

data from the Battery tide gauge (Manhattan) How Different is MMHW?

The Battery

NPCC Figure 4.B.6. Map (vs Longitude, Latitude) showing the difference between present-day tidal MMHW (monthly maximum) and MHHW (daily maximum) water levels. [email protected]

NPCC 2015/2019 Citizen Science/ Collaboration Ongoing/Future Research

• Collaborating with USGS (Ganju, Aretxabaleta) – Modeling the entire US East and Gulf Coast region’s tides with sea level rise – Mapping future monthly tidal flooding as pilot studies (Boston, Chesapeake, New Jersey) • Also interacting with NOAA/ W. Sweet • Key questions: – What methods/models can be used for nationwide monthly tidal flood mapping? – What is the best metric for mapping future frequent floods? Is it MMHW? Minor flood level? The 1-month return period flood? …. Define Uninhabitable! NYC Government Response

• NPCC’s 100-year flood zones plus SLR are already used in some planning/zoning • Was invited to meet with City Planning and Mayor’s Office of Resiliency in May – Not yet ready to add MMHW to their flood mapper or planning • Having two tidal flood metrics may be confusing • Also, useful to wait for more research defining what tidal flood metric is best – We are collaborating to map MMHW with NPCC’s other SLR percentiles (10th, 25th, 75th)

[email protected] Conclusions

• Across NYC, MMHW exceeds MHHW by 0.6-1.0 foot • MMHW is a substantially higher metric of tidal flooding, flooding neighborhoods sooner as sea level rises • While MHHW is exceeded hundreds of times per year, MMHW has only 20-35 exceedances per year and can better address a possible tipping point for habitability • Mapping relatively frequent and observable monthly tidal flooding may be more helpful than mapping the rare 100-year flood, for communicating the impacts of sea level rise

[email protected] Modeling and Mapping the Advance of Monthly Tidal Flooding A Possible Threshold of Inhabitability

Philip Orton, Stevens Institute of Technology

Primary Funding: NOAA-RISA [email protected] EXTRA SLIDES http://stevens.edu/SFAS Same NYHOPS model is applied in real-time ensemble flood forecasting http://stevens.edu/SFAS http://stevens.edu/SFAS