Shifting precipitation & extreme weather events

Climate change is altering patterns of precipitation in the Mid-Atlantic region, resulting in more intense flooding and droughts. The region is projected to have an increase in the amount of annual precipitation. However, precipitation will vary seasonally, and the region will experience more damaging storms that bring heavy amounts of precipitation. In general, precipitation is expected to increase in the winter and spring, while summer and fall projections vary.

Heavy precipitation events, characterized by intense rain or snow exceeding the average amount for a specific location and season, are becoming more frequent in the region. These events can cause crop damage, soil erosion, increased flood risks, and strain on infrastructure. They can overwhelm sewage systems, leading to overflow and stormwater runoff that pollute surrounding land and water bodies. Moreover, heavy precipitation events are less likely to be absorbed by drier soils, exacerbating the risk of flooding.

This rise in heavy precipitation contributes to deadly climate impacts—flooding. Devastating flash floods, such as the one in West Virginia in June 2016, where precipitation levels reached 1-in-1000-year events within 24 hours, highlight the severity of the issue. The deadly flash flood that killed 23 people was the result of 8 to 10 inches of rain falling within 12 hours. Heavy precipitation days are difficult to predict and challenge existing infrastructure. In September 2020, weather forecasting models failed to predict a heavy precipitation event in Washington, D.C. Within an hour, a half foot of rain led creeks and streams to rise to eight feet, flooding cars and standing people in overflown waters.

Alongside shifts in precipitation, extreme weather events are becoming more frequent and severe in the Mid-Atlantic region. Hurricanes, heatwaves, flooding, and droughts pose significant challenges to both communities and natural ecosystems. The increased annual precipitation and heavy precipitation events worsen the impact of floods. Storm events are becoming more frequent and intense, leading to catastrophic flooding. Coastal areas, such as Alexandria in Virginia, are particularly susceptible to flooding. King tide flooding, caused by strong winds pushing water toward the land, regularly impacts waterfront business districts. Nor’easters, storms that form along the East Coast around the Mid-Atlantic and Northeast region, are known for their strong winds, heavy precipitation, and coastal flooding. Droughts, on the other hand, result from reduced precipitation, leading to water scarcity, dry conditions, and potential wildfires.

What does this mean for national parks?

Parks can help mitigate some of the impacts of climate change. For example, parks can sequester carbon, reduce heat impact, and help lessen flooding. In particular, waterfront parks in urban centers serve as a natural buffer between the body of water and impermeable surfaces like roads. By storing water before the rainfall overflows into its surroundings, parks minimize the possibility of heavy precipitation turning into a flood. By collecting and slowing down water, parks also reduce stormwater runoff.

However, parks are very vulnerable to flooding. In June 2006, seven inches of rain inundated the National Mall, damaging the nationally important historical heritage site. A levee was built afterwards to prevent future flooding. However, more recently in 2019 and 2020, weaker storms flooded the National Mall again. Rebuilding national parks after flood events involved a costly and complex process. On the other hand, abnormally dry conditions can negatively impact wildlife by reducing water availability and fragmenting ecosystems.

Mitigation efforts and adaptation strategies are crucial in addressing the challenges posed by these shifts in precipitation patterns and extreme weather events. Protecting and preserving the natural habitats and ecosystems within national parks is essential to ensure their resilience in the face of these climate-related changes.