Longer and More Frequent Mid-Atlantic Heat Waves by Mid-Century

Changes in extreme weather events are an area of concern in the face of changing climate. Heat waves (periods of sustained, above normal temperature) are of particular interest given the heavy costs, not only in strain on infrastructure and utilities but also in loss of human life, they can engender (e.g. in the United States, 1995, 2001, 2010; in Europe, 2003, 2006, 2010). In many instances, the costs of heat waves are associated with insufficient local preparedness and infrastructure. With the Earth predicted to warm, future heat waves could be more frequent, sustained, or intense; therefore, preparation for such events might greatly reduce their societal impacts. This study focuses on potential heat wave changes in the highly populous (greater than 96 people/km²) mid-Atlantic region of the Eastern United States from Alexandria, VA through Washington, DC, Baltimore, MD, Philadelphia, PA, the entire state of New Jersey, New York, NY, Long Island, NY, and the entire state of Connecticut. A nested regional climate model (RegCM3) simulated future climate over this region at a 10 km horizontal resolution for two future emissions scenarios (SRES B1 and A1FI). Output from the NCAR CCSM3 drove the regional simulations for two fifteen-year windows from 2050 - 2064 and 2085 - 2099. The final decade of each simulation was averaged for analyses and compared to a 1990 - 1999 simulation. Under both future forcing scenarios, heat waves in the study region increase compared to the twentieth century. In the B1 simulation, the number of summer (June, July, and August average) days exceeding 37.8° C increased by up to 600% at mid-century and up to 200% at the end of the century; the duration of the longest summer heat wave (consecutive days exceeding 37.8° C) increased by up to 26 days at mid-century and up to 10 days by the end of the century. For the A1FI scenario, the number of summer days exceeding 37.8° C increased by up to 250% at mid-century and up to 1300% at the end of the century; the duration of the longest summer heat wave increased by up to 14 days at mid-century and up to 48 days by the end of the century. Both scenarios suggest that, in the 21st century, the most populous sector of the mid-Atlantic region will experience more and longer heat waves than in the latter part of the 20th century, with heat waves under the B1 scenario being most intense at mid-century (2055 - 2064 average) and those under the A1FI scenario being most intense at the end of the century (2090 - 2099 average). By suggesting a greater incidence of heat waves in the coming century, these results imply that planning in the highly populous mid-Atlantic region should include ensuring both adequate cooling capacity in the built environment and sufficient utilities to support such a substantial increase in summer cooling.