Rising sea levels are a widely recognized consequence of climate change, with the global average sea level setting a record high in 2022 at 101.2mm (4 inches) above 1993 levels. However, the extent of sea level rise varies widely across the world due to differences in the strength of wind and ocean currents. In addition, the impact of sea level rise on the frequency of coastal flooding varies widely due to differences in terrain, elevation and flow paths. Understanding potential coastal flooding risks is essential for companies and investors to help minimize business interruptions and property damage.
An estimated 40% of the world’s population lives within 100km of the coast, and recent figures suggest that up to 20% of global GDP could be at risk by 2100 due to coastal flooding driven by sea level rise under a high climate change scenario. This is driving the need for sophisticated analytics to support informed decision-making.
Projecting coastal flood frequency
S&P Global Sustainable1 has developed models to project coastal flood frequency across different climate change scenarios and time periods. The methodology incorporates three key components:
Flood frequency modelling: The frequency of a historical 1-in-100-year coastal flood is projected over time and across scenarios based on changes in sea levels and storm tide patterns. As the influence of climate change increases, a historical 1-in-100-year flood could become a 1-in-10-year event, increasing the frequency of damaging flood events tenfold.
High-resolution elevation data: Accurately measuring land elevation is essential to understanding flood risk, as properties above the projected flood depth are less likely to be impacted than low-lying properties.
Flood flow-path modelling: A flood flow path algorithm provides insight into whether inland locations are connected to the ocean via a low elevation flow path, and thus may be exposed to coastal flood risk.
Figure 1 below shows that coastal flood exposure (green) varies widely across Miami in the 2090s under the SSP3-7.0 climate change scenario. In this scenario, efforts to reduce global greenhouse gas emissions are limited and total emissions double by 2100, resulting in global average temperatures rising by 2.8 degrees C to 4.6 degrees C by 2100. Exposure is extensive in the barrier islands such as Miami Beach and Surfside, but more variable on the mainland to the west of Biscayne Bay where the flood-exposed areas follow the paths of waterways and other low-lying areas. The impact of coastal flooding can be different for properties just a few blocks apart, or even on opposite sides of the same street.
Figure 2 below illustrates the importance of accurately modelling flood flow paths. The first image shows that coastal flood exposure under the SSP3-7.0 scenario is limited primarily to the Eastern coast of southern Manhattan by the 2090s. However, an inland area to the west has much higher coastal flood exposure than neighboring areas due to its connectivity to the Hudson River via a low-elevation flood path. Coastal flood exposure is not limited to the immediate shoreline and not all waterfront properties will be exposed.
The coastal flooding models that reflect high-resolution elevation data and flow paths enable a detailed, realistic and granular assessment of coastal flood risk at the property level, helping companies and investors anticipate and plan for potential climate-related risks.