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Extreme Precipitation and Coastal Flooding in Northern New England: Impacts, Implications, and Intriguing Strategies

Tuesday, October 5, 2010 | 10:30 am
Ellen Douglass
UMass Boston


In this talk, I will present the results of two research projects related to extreme events and climate change in New England.  The purpose of the first study was to investigate the presence of trends in extreme precipitation (denoted MAXP and defined as the annual maximum daily precipitation depth) time series for coastal northern New England and to assess changes in the magnitude of the so-called“100-year storm”. The number of daily precipitation depths ≥ 2 inches (denoted as GT2in) was also quantified for each year. A trend analysis over the time period 1954-2005 indicated that MAXP was amazingly stationary; however, trends in GT2in were found at some stations. Most stations that had trends in MAXP also had trends in GT2in. The majority of stations in southern NH and eastern MA showed evidence of trends in MAXP (but not GT2in) for the time period beginning in1970. Next, the Generalized Extreme Value (GEV) distribution was used to estimate 100-yr precipitation depth quantiles for the 1954-2005 record which were then compared to TP-40 100-year, 24-hour precipitation depths. Stations in northeastern MA, southeastern NH and southern ME exceeded 8 inches and also exceeded TP-40 estimates by more than 2 inches. These findings indicate that TP-40 under-represents coastal storm depths and suggest the need for updating of design storm estimates. Furthermore, extreme precipitation events of longer than 1-day duration have caused large-scale flooding in the region over the last decade. We found evidence that the magnitude of longer duration storms (particularly 2-day storms) may also be increasing, calling for engineered infrastructure that can accommodate increases in both storm magnitude and duration. However, in designing for climate change, we must also consider the effects of infrastructure on the entire range of flows (particularly on low flow), in order to avoid repeating the past engineering mistakes of barriers to fish migration, stream fragmentation and alteration of aquatic habitats.
The second part of this talk will present results of research into the impacts of increased coastal flooding due to sea level rise on Environmental Justice communities (namely East Boston and Everett) in the metro Boston area.  One of our goals in the project was to better understand how the residents of each community viewed climate change in general and flooding in particular.  We also presented and got feedback on their attitudes to the range of coastal adaptation options of doing nothing, accommodation, retreat and flood protection. In East Boston, we presented conceptual designs of these options.  One of the major outcomes of this research has been the identification of obstacles and incentives to adaptation in each of our study communities.   Major obstacles to adaptation in these communities include convincing landlords of the need for adaptation, zoning constraints such as Designated Port Areas, the lack of engagement by commercial and industrial firms and lack of access to facilities and evacuation routes during a disaster.   Despite the unique circumstances and constraints in each community, two common obstacles emerged: 1) a lack of understanding about local impacts and the complexities of risks related to climate change and adaptation, and 2) a lack of information about where to turn for help.  After our series of meetings ended, a common incentive in all communities was an intense desire to be informed and to become active participants in planning and implementing climate change adaptation initiatives in their communities.