Flooding in Massachusetts

Excerpted from U.Mass and Massachusetts press release.

Our climate is changing, and that is impacting water. Though much has been made of the reduction in precipitation in the Southwest and water shortages, in truth, on average, total annual precipitation has increased over land areas in the United States and worldwide. Since 1901, global precipitation has increased at an average rate of 0.04 inches per decade, while precipitation in the contiguous 48 states has increased at a rate of 0.20 inches per decade.

Massachusetts has one of the most robust records of hydrological variables, such as precipitation and groundwater levels that goes back many decades. Studies this century suggest that climate will change the timing and nature of precipitation- alteration in thy hydrologic cycle.

Although few observational studies on ground water and climate have been done, in 2010 a group from the University of Massachusetts used the state’s wealth of data to examine the response of the water table to the last 60 years of climate in New England. That work by Boutt and Weider at the University of Massachusetts - Amherst found that since 1970, precipitation has increased in New England by 15–20%. Due to the geology in New England , this increase in precipitation is leading to a rapid rise in groundwater levels. In some parts of Massachusetts are seeing the water table rise by a few centimeters every year. While this value may seem small, the cumulative rise over decades can begin to affect sub-surface infrastructure.

Dr. David Bout head of the Hydrogeology Group at University of Massachusetts- Amherst and a professor of Earth, Geographic and Climate Sciences (EGCS) has been studying the impact of our changing climate on groundwater since 2005. Recently, the work being done by his group caught the eye of the state’s Executive Office of Energy and Environmental Affairs and Department of Conservation and Recreation, both of which asked Boutt and his colleagues to build a new model that could assess flooding risk from groundwater rise to improve that model with data from an ongoing statewide survey and to file a final report, which the group is in the process of completing.

To date their conclusions are that shallow groundwater in Massachusetts will rise by an average of 0.14-0.8 ft in the coming  years. The Groundwater Rise Risk Zones will increase groundwater flooding by 8-16%, groundwater emergence will increase by 7-14% and groundwater shoaling will increase by 4-8%. University of Massachusetts- Amherst expects the greatest groundwater risks to occur in Western Massachusetts.

 

Types of Groundwater Flooding

• Groundwater rise: Movement upward of the water table due to short or long-term fluctuations in rainfall recharge and/or river, ocean or tidal levels.
• Groundwater shoaling: Water table rise in the subsurface closer to, but not reaching, the land surface.
• Groundwater emergence: Discharge/outflow of groundwater at the surface from the subsurface due to the rise of the water table at a point (spring) or diffuse locations.
• Groundwater flooding: Temporary process of the rise of the water table resulting in a groundwater emergence where the water level surface intersects or goes above the land surface due to a changing condition.

From U.Mass presentation and quoting Bosserelle et al., 2021, Earth’s Future