Preparing for the 100-Year Storm: The Price to Adapt Residential Buildings to Flooding From Accelerated Rainfall and Sea Level Rise in Cambridge, Massachusetts by 2070

Abstract

Flooding is a leading billion-dollar disaster in the United States from lives lost, ecosystems disrupted, and properties damaged (NOAA, 2022). American cities are responding to hurricanes and rising tides accelerated from climate change by launching home protection plans. As individuals and taxpayers bear the cost of storm preparation, the variety of adaptation choices can be confusing. Should homeowners pay for flood insurance, elevate their living quarters, wait for repairs after a storm, or relocate their lives entirely? The fees to floodproof are often obscured on vendor websites and hidden in non-peer-reviewed literature (Aerts, 2018; Boynton, 2016; FEMA, 2023a). Communities need confidence that investing in private flood adaptations will pay off against the pain of evacuation. To help homeowners make informed decisions on emerging flood adaptations, this research analyzed neighborhoods in Cambridge, Massachusetts at risk of inundation by 2070 and estimated the costs to respond in the face of a 100-year storm. My two main research questions were: (1) Where and who are at the highest risk of flooding from climate change? And (2) what is the best course of action for homeowners to protect their residential property between three scenarios: assume repairs following a storm, retrofit buildings, or relocate?

I designed a flood hazard map using ArcGIS to capture individual property features, values, occupant demographics, and flood projections from rainfall and sea level rise. Flood insurance was assumed for sites required to enroll if built inside a federally designated, high-risk FEMA special hazard flood area, with insurance rates determined by the City of Cambridge digital flood insurance rate map (City of Cambridge, 2023d). Insurance was not assumed for homes beyond these boundaries. I applied the Cambridge City Base (CCB) datum in all measurements to match the Cambridge standard for reporting ground elevation. CCB measures 3.6 m (11.65 ft) below the federal North American Vertical Datum (NAVD) which lies ~0.3 ft above the mean sea level in Boston (City of Cambridge, 2022). I found that Cambridge buildings at 21.9 m CCB (72 ft) altitude or higher are safe from flooding through 2070, meanwhile property below this elevation will face a range of inundation (City of Cambridge, 2022).

My findings showed that Cambridge has five most vulnerable, residential neighborhoods to flooding: Cambridge Highlands, Wellington-Harrington, The Port, East Cambridge, and Cambridge Port. All five locations anticipate over half of its properties to partially flood in less than 50 years. Flooding will affect the city’s wealthiest residents earning over $160,000 a year to its poorest earning $30,000 a year, inclusive of all races, ethnicities, and English language proficiency. Coastal and inland flooding will impact people from every socioeconomic background.

Using the hazard map to calculate flood exposure, a micro-scale benefit-cost analysis was applied to 15 random homes to estimate the cost disaster response. I measured affordability of responses against the neighborhood’s median income—a known driver for individual action. Among the 15 sample sites in floodplains, a residential building can cost $7,200–$103,300 to retrofit for flood protection through 2070 compared to a wider range of $2,800–$204,200 to repair the home after a storm (Durante, 2020; FEMA, 2022c; Miguelez, 2022). In contrast, moving intrastate to a safer location was estimated to cost $532,700–$10 million (City of Cambridge, 2024; Snow, 2024; Zillow, 2019).

A benefit-cost analysis was applied to three flood preparation options to find which decision was financially favorable through 2070. Both repair and retrofit’s benefit-cost ratios were greater than one and recommendable for Cambridge homeowners, whereby relocation ratio was less than one and not advised without external financial support. The capital investment for a home flood upgrade or relocation makes the current city guidelines unaffordable for most local median income earners—contradictory to the plans of the city. As 45% of Cambridge properties may experience partial flooding by 2070, creating further resources to support the cost of living with climate risks will become critical preparation for the 100-year storm.