High-Tide Flooding Having Lasting Economic Impact on Flood-Prone Communities, Study Finds

A study by Stanford researchers, published in the February 15 issue of Science Advances, found long-term economic effects from frequent high-tide flooding in coastal communities. The study focused on Annapolis, Maryland, near the Chesapeake Bay, although a number of other coastal communities, such as Miami Beach and Virginia Beach, experience high-tide flooding events (also known as nuisance flooding and sunny day flooding). In Annapolis, minor floods reduced consumer visits to downtown businesses by 37-38 percent; moderate floods reduced visits by 63-65 percent; and major floods reduced them up to 89 percent.

High tide flooding is happening more often and its frequency will only increase. According to the study, high-tide floods in coastal communities occurred an average of 11.8 days per year from 2006 to 2010, up from 2.1 days from 1956 to 1960. By 2035, the average is expected to increase to more than 26 days in 170 communities. The researchers note that these incidents “often last for just a few hours at a time and rarely leave lasting infrastructure damage,” thus making their impact harder to trace.

Focusing on Annapolis, Maryland, the researchers compiled a combination of social media, photography, and video evidence along with precipitation and tide gauge data to cross-reference when high-tide flooding events occurred. Based on the nuisance flood threshold in Annapolis, the researchers defined three distinct flood severity ranges that differ from those established by the National Weather Service: “minor (1.73 to 2.03 feet), moderate (2.03 to 2.33 feet), and major (>2.33 feet).” The scientists then examined parking lot usage in the historic downtown area of Annapolis as a proxy for the number of visitors to the area. By combining the information gathered about the number of parked cars and the number of nuisance-level floods, the researchers were able to evaluate the impact of floods on economic activity. They concluded that high-tide flooding reduced visits to downtown Annapolis by 1.7 percent, which would suggest a 1.7 percent shortfall in economic activity.

When high-tide flooding is adjusted to the projected rise in the Chesapeake Bay's water level (due to climate change), the researchers found that flooding severity and frequency would increase, and visits to the area would continue to decrease.

This case-study demonstrates the importance of implementing resilient infrastructure in the wake of global sea level rise. Although the study does not mention specifics to improve resilience, local governments can take steps to make buildings watertight (to the extent required), elevate structures above the minimum required level to avoid flooding (the freeboard level), and incorporate green infrastructure which helps reduce runoff. By making adaptations to the existing infrastructure, communities can lessen the impacts of climate change on their economies. The National Institute of Building Sciences has found that investing $1 in mitigation measures can save as much as $11 in future disaster costs.

 

Authors: Cameron Bechtold and Nicolette Santos