A Deluge in the DMV: Climate Change and Intensifying Rainfall in Northern Virginia

It’s been a rainy August, and you may feel like this is more than the usual summer showers. It’s not just an off year; research shows that rainfall has increased worldwide over the past decade. The culprit behind these downpours is climate change, the villain in many natural phenomena. Don’t worry, it’s not all doom and gloom; science also helps us understand how we can be better prepared to handle heavy rainfall.

Climate change is often seen as rising temperatures that melt ice caps and, in turn, raise sea levels. One may not suspect it, but for the past 10 years, scientists have studied how extreme temperatures in either direction caused by climate change have affected the amount of rainfall we receive. 1 out of every 4 extreme rain events that happen on Earth is due to climate change. Over the last 3 years, the national news has been filled with catastrophic rain events that caused flooding, including flash flooding in West Virginia, central Texas floods that resulted in loss of life, and even flooding in the DC-metro area.

What about rising temperatures causes this phenomenon? Rain is water absorbed into our atmosphere through evaporation and transpiration; heat from the sun causes water on the surface of bodies of water to evaporate into the sky. Trees and other plants also give off water as a byproduct of photosynthesis. This vapor makes up clouds; water vapor is just light enough to stick to specks of dust in the atmosphere and form a “fluffy” (most likely wet and soggy) cloud. Water droplets stay in the sky until they collect enough water, making them larger, heavier, and more likely to fall to Earth as rain. Warmer air can hold 7% more water in the atmosphere, and the Earth has been warming by 25ºC each year since 1970.The atmosphere today can collect and store more water vapor than before; instead of several light to normal showers over a season, we now get infrequent bursts of heavy rainfall. Not only does more rain fall to the ground, but it also comes in greater volumes and harder because larger droplets fall. Climate change is a double-edged sword: while it can cause rainfall that results in flash flooding, the higher evaporation rate also causes drought. In arid areas, high heat evaporates water and even pulls it from the soil. When it does rain, this cracked, dry soil can't absorb the downpour effectively, as cracks channel water elsewhere, and a thick outer layer can form, making it hard for water to be absorbed. Many states in the U.S. experience a “weather whiplash” where extreme heat causes drought, and then suddenly intense rainfall causes flooding. This happened in Texas last summer.  In California, vegetation drinks up the rain and multiplies, but when drought hits, it creates a perfect supply of dry tinder for wildfires.

Flooding happens when rain has nowhere to go; impervious surfaces in cities and neighborhoods, like asphalt, concrete, and glass, cannot absorb rainfall. We can channel rain to sewer networks, but even those get overloaded. This also pushes out wastewater and untreated sewage into our waterways.  Much of Virginia’s infrastructure is built to withstand predicted rainfall, but these models did not account for how quickly the Earth is heating, nor do they consider rapid growth of the area’s development and population. Rainfall predictions that set federal engineering standards for the State of Virginia were created in 2006, and they have not been revised since. Many organizations have taken matters into their own hands by creating their own rainfall prediction models, such as the Chesapeake Bay Trust’s model.

In Northern Virginia, this past month brought 3.5 inches of rain, triple the region's average.  For our friends at the Four Mile Run Conservancy, rainfall caused flooding that destroyed a brand new kayak launch just last week. Rain is often associated with doom and gloom, and the news that rainfall can only get worse with climate change probably doesn’t put a smile on your face. But there is hope! Nature provides all of the defenses we need against extreme weather. Lush green grass and soft soil can absorb and filter our rain. Additionally, minerals in the ground filter water before it flows into water sources. You can even simulate this on your own property by creating a rain garden with native plants!

Having protected landscapes that are allowed to grow how nature intended provides ample area for water to be absorbed or channeled into a safe location like a river or valley. A significant portion of the Northern Virginia region is part of the Potomac watershed, because rainfall drains from that area into the river. This watershed stretches across Northern Virginia, West Virginia, Pennsylvania, D.C., and Maryland, with the DC metro area hosting 81% of the population living in this basin. This watershed is our lifeline during heavy rains. 

At NVCT, landowners often approach us seeking to protect their land. Another way we find land to conserve is by identifying land that is not yet protected and has features that will benefit people in our region. One feature we focus on is watershed protection. Our geographic information systems (GIS) mapping tools allow us to identify unprotected land within the Potomac watershed and see what other features it has, like whether it contains wildlife habitat or borders an existing park. With a small team and a focus on local conservation, we strategically conserve the land that will have the greatest impact for residents in our region. Rain may not be something we can control or change, but we can be prepared for it. Protecting forests, wetlands, open spaces, and healthy soil gives rain somewhere to go before it casuses a flood. By conserving land within the Potomac watershed, NVCT is helping protect not only wildlife and natural landscapes, but also the communities that depend on them. We hope you will join us in this fight.