Climate is one of the most important factors influencing general vegetation patterns—whether those climate trends are broad-scale, extending across large parts of continents, or very local microclimates, varying within a single valley.
Rock Creek Park is located in the Mid-Atlantic region of the United States, in Washington, D.C. Situated about 30 miles (about 50 km) inland from the Chesapeake Bay as the crow flies, this area is influenced by both continental and coastal weather systems, and experiences a temperate seasonal climate. Spring and fall are mild. Winters are cold but not severe, with average low temperatures of 30 degrees (-1 degree C) between December and February, and infrequent snows. Summers are hot and humid with average high temperatures in the upper 80s (lower 30s Celsius) between June and August. With an average annual rainfall of nearly 44 inches (about 110 cm) over the last 30 years, this is the sort of climate that generally supports forests. There are about 200 days of adequate daylight, warmth, and moisture for most plants to grow (often called “the growing season”).
Severe weather shapes the landscape and vegetation of Rock Creek Park. Tornadoes are infrequent. However, commonplace summer thunderstorms can bring high winds and torrential rains that cause flooding and severe erosion. Strong windstorms of any kind have the potential to uproot entire trees, especially in shallow-soiled parts of the park’s landscape.
Late summer or fall hurricanes are rare, having often weakened by the time they reach this far inland; however, the effects of 1972’s Hurricane Agnes can still be seen in the area today. Occasional winter storms such as “nor'easters” can bring intense cold winds and freezing precipitation.1 Tree limbs can break under the accumulation of ice and snow.
Changes to regional and global climate continue to emerge as a major threat to the continued survival of many species and the natural communities of which they are a part. Scientists are currently trying to understand the ecological implications of near- and long-term changes. While the scope and severity of the impact on the plants and animals of Rock Creek Park are unknown, climate change is certain to affect which natural communities will thrive at Rock Creek Park in the future. For more information, see Climate and Weather (Stewardship and Ecological Threats).