Sea level rise is taken seriously in New York city. According to a survey, 37% of lower Manhattan will be exposed to storm surges by 2050, and official estimates for 2100 have not yet been published. Sea level rise is accelerating and exacerbating the potential for catastrophic flooding as time passes.

Earth.Org has mapped what a severe flood would look like in New York city by 2100.

New York’s coastline is a staggering 837 kilometres long. Building defences on such a scale will be a gargantuan task, but one that the city must undertake nonetheless. Low-end estimates for sea level rise by 2100 double the amount of citizens exposed to a 1-in-100 year flood (a flood whose intensity has a 1% chance of occurring in any given year).

The mayor Bill de Blasio announced a USD $10 billion defence plan last year, although the funds aren’t entirely accounted for. Even more doubtful in light of USD $27 million of planned investment for Hurricane Sandy recovery than never came through. 

The plan involves elevating parks, building removal flood barriers, a five-mile seawall around Staten Island and sand bars around the rockaways. The lower tip of Manhattan, most at risk, cannot accommodate flood barriers. The proposed solution is to develop two adjacent blocks of elevated land encapsulating the point and protecting it from future surges.

To better understand why this infrastructure is considered essential, despite the massive costs and onerous nature of the work, Earth.Org has modelled what extreme flooding could look like in New York by 2100.

Sea Level Rise 2100 New York City

Sea level rise projections by 2100 for two scenarios with the amount of rise in meters indicated (mild = 2m; extreme = 5m). Percentage and total population displacement indicated bottom right.

Methodology

Global mean sea level is projected to rise by 2m at the end of this century. However, in order to determine local sea level rise (SLR), one has to take into account local coastal flood levels which could be 2.8m above Mean Higher-High Water (MHHW) at extreme forecasts. These local levels bring variability to the projected SLR from 1m to 6.5m (eg. Rio vs Kolkata).

The SLR scenarios used in this study are based on the forecasts from Climate Central – Coastal Risk Screening Tool  with the following parameters:

Sea level Projection Source: is from two highly cited journals by Kopp et al., estimating SLR mainly due to ocean thermal expansion and ice melt. The mid-range scenario projected 0.5-1.2m of SLR based on different representative concentration pathways (RCP) defined by the IPCC. While the pessimistic scenario added more mechanisms of ice-sheet melting, estimating SLR at 1m-2.5m in 2100, with projection of 10m SLR at 2300.

Coastal Flooding: More frequent coastal flooding is a direct impact of sea-level rise. Based on the Global tides and surge reanalysis by Muis et al., (2016), it is estimated that the extreme coastal water level could be from 0.2 – 2.8m over mean level. While in extreme cases like China and the Netherlands it could experience 5-10m of extreme sea levels. Here, the coastal local flood level is added on top of the projected SLR.

Pollution Scenario: allows to choose the RCP, the greenhouse gas concentration trajectory defined by the IPCC.  The mild level is based on RCP4.5, of 2°C temperature rise; while Extreme level is based on RCP 8.5, of 4°C temperature rise.

Luck: applies to the the baseline SLR, defined in the “Sea level projection” section, upon which we add flooding. “Mild” refers to the mid-range scenario of 0.5-1.2m, and “extreme” to the pessimistic scenario of 1-2.5m. We used the high-end value of each scenario (mild = 1m; extreme = 2.5m).

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