You’ve examined climate trends at the global and national scale and you’ve learned about the hazards associated with extreme weather events. Now it’s time to look at impacts closer to home. What does climate change mean for Pennsylvania? How will it affect the southeastern region’s urban areas, rural farming communities, and the coastal and riverine ecosystems along the Delaware and Schuylkill rivers? Which neighborhoods are more likely to flood? How much hotter will summers in the city be?
The Current Climate
If you look at recent trends in temperature indicators, Pennsylvania’s climate is already shifting. Day-time and night-time temperatures are increasing. Across the northeast average temperatures have risen 1.5°F since 1970, but Pennsylvania’s average temperature has risen 2.1°F over the same time period (1,2). Philadelphia is experiencing 18 fewer cold nights (below 32F°) than it did in 1970 (3). With higher day-time highs and warmer night-time lows, the number of extreme heat days is expected to increase, particularly in urban areas that are already prone to the heat island effect.
Growing Flood Risk
From waterfront business districts to low-lying inland areas, flooding from extreme precipitation events is also a growing concern for Pennsylvania. In the northeastern US, there has been a slight upward trend in the annual number of extreme precipitation events over the past 30 years (4). Even though the trend is slight, the impact from a single flooding event can be devastating for a community. During the historic flood of 1971, eleven inches of rain fell in Delaware and Montgomery counties. The flooding caused $17.6 million in damages in the City of Chester.
The Future Climate
Using the most current climate models from the International Panel on Climate Change (IPCC), scientists are predicting the changes that Pennsylvania will experience over the next 50-100 years. Their projections can help us determine the likelihood of future extreme events and the magnitude of change in temperature, precipitation, and sea-level rise. With a better idea of how much, how often, and how intense, we can take action to plan for and minimize the risks associated with extreme weather events and sea-level rise.
Climate Predictions and Potential Impacts for Pennsylvania:
Temperature: Pennsylvania’s average temperature is rising. By 2050, the annual temperature will be 3°C (5.4°F) warmer than at the end of the past century (5). Urban areas, like Philadelphia, will experience greater increases in average temperatures. Night-time temperatures are also expected to be higher; this trend will contribute to hotter day-time temperatures and provide less relief from extreme heat events.
Extreme Heat Events: Heat waves will increase in frequency, severity, and length. Across Pennsylvania, the average number of extreme heat days (days above 90°F) is predicted to more than double by 2050. The southwestern and southeastern regions currently experience about 20 days above 90°F per year. By 2050, these regions will likely experience more than 50 extreme heat days per year (1).
Precipitation Patterns: While many places in the United States will experience more droughts, the Northeast is expected to be wetter. Precipitation will vary by season, with the greatest increases in winter, spring, and fall. Predicting which state or region will receive more snow or rain and how much more is challenging, however. Precipitation models have been shown to provide more accurate forecasts over larger areas (>1200 miles) than for individual states or cities (7).
Severe Storms: The frequency and strength of thunderstorms and downpours will increase, leading to localized flooding (5).
Coastal Storms: While the number of coastal storms in any given year will not increase, they are expected to be stronger and produce heavier rainfall (5). The $65 billion in damages to homes, businesses, and infrastructure during Hurricane Sandy is just one example of how devastating storm surge and flooding from coastal storms can be.
Sea-Level Rise: States in the Mid-Atlantic are experiencing some of the fastest rates of sea-level rise in the world. In low-lying areas along the Delaware and Schuylkill Rivers, sea-level rise is intensifying localized flooding. Today, Philadelphia experiences about 20 flooding events each year. Based on a moderate projection for sea-level rise, Philadelphia may experience 10 times that many flooding events per year by 2045 (6).
Health: As heat waves linger and the number of extreme heat days soars, Pennsylvania’s residents will be at greater risk of heat-related illness and/or death. However, since more families are installing air conditioning in their homes, mortality rates due to extreme heat events will continue to fall.
In the summer, increases in ground-level ozone concentrations will cause Pennsylvania’s air quality to become worse. The levels of pollen and mold allergens circulating in the air may also increase with higher temperatures and rainfall amounts (5). Higher ozone and allergen concentrations put children, the elderly, and those with respiratory and heart problems at greater risk.
As Pennsylvania’s climate warms and precipitation increases, cases of mosquito-borne diseases like Zika virus, West Nile Virus, and Eastern Equine Encephalitis are also likely to increase. Illnesses associated with pests like ticks and cockroaches may also become more common (8).
Zhang, F., W. Li and M. E. Mann, 2016: Scale-dependent Regional Climate Predictability over North America Inferred from CMIP3 and CMIP5 Ensemble Simulations. Advances in Atmospheric Sciences, 33, 905-918.
Vision 2020 Climate Adaptation Plan for the City of Chester. (2014)