Introduction
The Boston Water and Sewer Commission (BWSC) has developed a Citywide model to simulate a variety of wet weather events and flooding scenarios that could occur in Boston. The results of this project may help inform the City's efforts to prepare for the effects of climate change, sea level rise, and more intense storm events. This website may also serve as a reference for City residents, businesses, and others who wish to learn more about how coastal flooding and rainfall have the potential to cause flooding and impact the City.
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The results presented on this website represent predictions that are based on data used by several City agencies for planning purposes. As predictions for Sea Level Rise and the impacts of climate change may change in the future, the data on this website may need to be updated accordingly. The predictions shown on this website do not forecast impacts from specific future events that have not yet occurred and should not be used for specific emergency actions or other purposes.
Storm Types and Sea Level Rise
To accurately represent the types of storms that may impact the City, BWSC analyzed over 70 years of rainfall data from Logan Airport and identified over 3,100 different storm events. Through this analysis, BWSC identified four different types of storms. Each one of these storm types has a distinct pattern of movement over the City and results in different amounts and intensities of rainfall.
Sea Level Rise and Storm Events
This study considers predicted Sea Level Rise by 2030 and 2070. The sea level rise predictions used in this study assume that emissions of greenhouses gasses continue to grow at current levels.
Thunderstorms, sometimes called "Airmass storms" by meteorologists, are relatively quick, high intensity events that result in significant rainfall at the start of the event. The burst of rainfall associated with these storms has the potential to cause widespread street flooding, but these storms are not typically associated with coastal flooding.
Nor'easters are low pressure systems that occur along the east coast of the United States. These storms are often associated with significant rainfall, strong winds, and coastal flooding. Boston has experienced several nor'easters in recent years, including the "bomb-cyclones" which occurred in early 2018.
Frontal storm events are common storms that include intense rainfall and strong winds. Frontal storm events occur when a mass of warm or cold air (a "front") sweeps across the City. These events are not typically associated with coastal flooding.
Tropical storms (hurricanes and other tropical systems) originate in the tropics and move north along the East Coast. These large, low pressure systems typically bring intense rainfall, wind, and storm surges to the areas they impact. Boston has been impacted by many hurricanes in the past, including the 1955 Hurricane Diane which inundated the City with nearly 10 inches of rain in less than 24 hours.
2D Model Simulations and Assessment of Critical Infrastructure
Impacts to critical infrastructure such as evacuation routes, hospitals, and MBTA stations were assessed throughout the City. The impacts to the City vary for each storm. The figure below displays the types of infrastructure for which BWSC determined impacts.
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This figure also depicts the areas of the City that BWSC simulated in 2D vs. 1D. The 2D modeling allows BWSC to predict the movement of water over the ground surface of the City whereas 1D modeling allows BWSC to predict where the City is vulnerable to flooding at locations where the capacity of the sewer or drain network is exceeded. The most flood vulnerable parts of the City were simulated in 2D during this initial study, and the whole City was simulated using BWSC's 1D sewer and drain models.
Frequently Asked Questions
Question: Will the flooding predicted by the Inundation Model occur in the future?
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Answer: The Inundation Model predictions represent a range of possible future scenarios based on current climate predictions and modeling. As climate predictions continue to improve, and the Commission revises the Inundation Model, the current predictions may change.
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Question: Does the Inundation Model account for Climate Ready Boston or other adaptations?
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Answer: No. The Inundation Model does not account for any adaptations currently being planned by the City or the Commission. The Commission is currently undertaking a project to evaluate these factors.
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Question: What type of storm does the Commission typically use to evaluate the performance of its infrastructure?
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Answer: The Commission’s standard design storm is a 10-year, 24-hour storm with 5.15 inches of rain. In addition to simulating this storm with the Inundation Model, the Commission also simulated a 10-year thunderstorm (“airmass”) event, which produces similar peak rainfall intensity. Predictions from the Inundation Model indicate that the flooding that results from the 10-year thunderstorm is nearly identical to flooding from the 10-year design storm. Results from the 10-year thunderstorm simulation are viewable below.
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Question: Why does the model predict different amounts of flooding in areas upstream of the Charles River dam in 2030 and 2070?
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Answer: Due to Sea Level Rise (SLR) that is predicted to occur between 2030 and 2070, the water level within the Charles River Basin may be higher during some rain events according to model predictions. In some locations, this may make it more difficult for the Commission’s system to discharge stormwater into the river, resulting in pockets of increased flooding. For a small number of scenarios, combined SLR and storm surge are predicted to overtop or flank (go around) the dam. In these scenarios, flooding upstream of the dam is significantly increased.
2D Model Simulations and Assessment of Critical Infrastructure
The Inundation Model viewer displays maps of flooding within the City of Boston under different storm and sea level rise scenarios. Follow the numbered boxes at the bottom of the viewer to determine the inundation scenario. First, choose one of the four extreme weather events to view. In the second box, click to select the amount of rainfall occurring in the storm over the labeled time period. In the third box, choose to use the sea level rise projection (with storm surge, if applicable) for either 2030 or 2070. There is an optional switch at the bottom of this box to compare 2030 and 2070 scenarios simultaneously – with this turned on, the 2030 sea level rise will appear on the left with the 2070 sea level rise on the right. The fourth box gives instructions for clicking on the yellow circle icon to view 360 images and will render a preview of the image if an icon is selected. The fifth box provides a count of the number of critical facilities that would be inundated given the conditions specified in boxes 1-3. There is an optional switch in the upper-right corner of the map to add critical facility locations to the map view. For a better viewing experience, open the embedded content in a new tab.