Cambridge, Mass., kicked off its latest sustainability initiative in 2012 after heavy spring rains and a record number of hot summer days. When Superstorm Sandy hit the East Coast a few months later, the city’s ongoing research on future public works needs was vindicated.
In November 2015, the city released the first fruits of this effort: an analysis of infrastructure most at risk from increasing heat and precipitation.
Like many cities, Cambridge has focused on reducing greenhouse gases. Although experts now believe some climate change is irreversibly locked in, lowering emissions remains important because it mitigates the planet’s scientifically demonstrated trend toward warmer conditions.
Based on this understanding and growing public concern, the city decided to assess potential impacts and prepare a comprehensive, multiyear resiliency plan. The results enable infrastructure professionals to sort through and compare multiple assets, systems, and populations to identify the most critical and urgent needs. Since resources are finite, they’ll be able to prioritize mitigation investments.
“Our stormwater infrastructure — pipes, manholes, and catch basins — are designed for storm patterns of the past,” says Public Works Commissioner Owen O’Riordan. “Climate change is expected to significantly increase rainfall, which would lead to expansion of the areas at risk of flooding and the depth of floods. We’ll need new strategies to deal with future conditions.”
Cambridge isn’t a coastal community. However, almost 100,000 people live within 6.43 square miles, making the city very dense. It’s also very old — people began settling there in the early 1600s — and located on the Charles River, which has been flooding more often.
Home to world-renown educational institutions like Harvard University and the Massachusetts Institute of Technology, the city has been a pioneer of sustainability policies and practices since joining ICLEI - Local Governments for Sustainability in 1999.
The city kicked off the Climate Change Vulnerability Assessment (CCVA) in September 2012 with three goals:
- To reach a common understanding about what climate change means to the city
- To support and spur preparedness discussion across the city
- To develop a Climate Change Preparedness and Resiliency Plan.
To maintain transparency, the city formed two advisory committees: an Expert Advisory Panel of climate scientists and policy experts from local academic institutions to guide assessment methodologies; and a Technical Advisory Committee representing businesses, state agencies, and residents.
Also, almost 1,000 residents participated in more than 40 meetings.
The report released in November 2015 shows that climate trends pose real risks. Precipitation-driven flooding in particular threatens infrastructure, as well as public health and safety, the economy, and quality of life.
Part 1: Precipitation-driven flooding
Because the science of climate change is constantly evolving, the city needs a framework that can be easily updated. Our customized multistep assessment included:
- Identifying critical infrastructure assets, community resources, and vulnerable populations
- Identifying threats and scenarios by time horizon and hazard type
- Developing risk scores for individual assets and systems as well as system interdependencies
- Identifying priority planning areas, the most at-risk services and populations with respect to climate change.
To translate how global trends will present at the local level, rain and temperature trends from sources such as the World Climate Research Program and 2014 U.S. National Climate Assessment Report were downscaled using historic data from local weather stations. The results provided temperature, relative humidity, and precipitation projections that we used to develop three planning horizons: present, 2030, and 2070.
GIS technology analyzed primary impacts as well as cumulative and cascading points of failure. Assessed both qualitatively and quantitatively, the impacts were then translated into vulnerability and risk scores for infrastructure assets and systems, community resources, and populations using a ranking system tailored for each system and their interdependencies.
The scenarios found that infrastructure vulnerability is highest during a precipitation-driven flood, a scenario that will become more frequent, intense, and expansive. Preliminary results indicate 100-year storm at-risk area will almost double by 2070.
In addition to 100-year events, both short- (one to two hours) and long-duration (48 to 72 hours) storms are projected to become more frequent. Cambridge has already experienced flooding from such events. On July 10, 2010, 3.6 inches of rain fell in one hour, exceeding stormwater system capacity and flooding several neighborhoods.
To assess vulnerability, it was necessary to delineate the extent and depth of flood risk. The 10- and 100-year storms were used to provide low and high precipitation-driven scenarios for 2030 and 2070. The resulting maps helped identify the neighborhoods, streets, and individual structures most at risk.
Finally, the models prove that flooding transcends jurisdictional boundaries.
Recognizing this, Cambridge, the City of Boston, the Boston Water and Sewer Commission, Massachusetts DOT (MassDOT), and Massachusetts Department of Conservation and Recreation have shared data and information and coordinated assumptions for mutual studies.
Once the climate projections were developed and scenarios for 2030 and 2070 made, the team “stress tested” 500 energy, critical services, telecommunication, roadways and bridges, transit, and water/stormwater locations.
For example, the present 25-year rainstorm, which has a 4% chance of occurring in a given year, which is associated with 6.2 inches of rainfall in 24 hours, is likely to have a 10% chance of occurring by 2070. Also, the 100-year rainstorm of today that is associated with 8.9 inches of rainfall in 24 hours will intensify to have 11.7 inches of rainfall in 24 hours by 2070.
Part 2: Sea level rise and storm surges
Cambridge partnered with MassDOT to explore the impact of sea level rise and more intense and frequent coastal storms. This model was unique because it considered the operations of the Charles River and Amelia Earhart dam, both of which are important flood barriers.
Also, the MassDOT model included future storm climatology based on future climate change scenarios. An integrated model that links sea level rise, river flooding, and piped infrastructure was developed to better understand impacts from different types of storms. Future flood elevations and depths were based on projected storms, which increase in intensity and frequency.
Risk-based models use a Monte Carlo approach to simulate a statistically robust set of tropical storms such as hurricanes and extra tropical storms such as nor’easters for each sea level rise scenario. Simulations until 2050 are based on present climate; after 2050, 21st-century climatology is used.
To build the models, we relied on the 2014 National Climate Assessment Report, which was prepared by 300 experts guided by a 60-member Federal Advisory Committee and reviewed by the National Academy of Sciences, industry experts, and the public.
The subsequent models predict 8 inches of sea level rise by 2030 and 3.4 feet by 2070. The chance that a storm surge will reach Cambridge by 2030 is less than 0.1%.
The 2070 predictions are scheduled to be published in CCVA Report Part 2 in June 2016.
Prioritizing resources and preparedness planning
Using a standardized methodology enabled the comparison of infrastructure systems with disparate categories, such as public health and vulnerable populations, as well as the opportunity to assess interdependencies.
The team concluded that the potential cascading impacts of failure of different systems is a significant issue that the city could experience. For example, loss of electricity may be the most important factor leading to wide ranging, cascading effects because it affects heat and air conditioning, transportation systems, and communications.
The assessment is the technical foundation for the city’s first Climate Change Preparedness and Resiliency Plan, a two-year effort starting in 2016.
In addition to developing strategies to protect the most affected assets, systems, and populations, the plan will evaluate the role of municipal buildings, such as City Hall, where people can gather to ask for and provide help during extreme events. To that end, the city will develop pilot neighborhood plans that consider resilient strategies for community planning and public health and revised design criteria for infrastructure and building improvements.
“It’s not only about disasters like Hurricane Sandy; it’s also about how changing weather patterns affect how things work,” says John Bolduc, environmental planner for the city’s Community Development Department and the report’s project manager.
Indrani Ghosh is climate risk and resiliency project technical lead for Kleinfelder (www.kleinfelder.com). Nathalie Beauvais, International AIA, AICP, LEED AP, is a senior planner project manager for climate change projects for Kleinfelder. E-mail email@example.com and firstname.lastname@example.org.