Climate Fact: River Temperature Rise
Earth Gauge Video is available for this tip.
In Brief: Temperatures in local waterways are rising from a combination of factors.
Moving from Chicago to Baltimore, where the average temperature is about ten degrees Fahrenheit warmer, might take a little bit of adjustment but almost certainly wouldn’t be fatal for humans. Most fish and other aquatic species, however, would not survive an equivalent temperature change. Warmer water temperatures have contributed to the elimination of the Brook Trout from many streams in the eastern U.S. In the mid-Atlantic region, temperatures are becoming intolerable for some sensitive species like the Longnose dace and Cutlips minnow. Temperatures are beginning to enter the danger zone even for the relatively tough and tolerant Blacknose dace, the most common species in the region’s urban streams.
Annual mean water temperatures in the nation’s streams and rivers are increasing at an average rate of 0.016 and 0.139 degrees Fahrenheit per year, respectively. The Potomac River around our Nation’s capital is seven degrees warmer than it was in the 1920s and the Delaware River around Philadelphia is 4.5 degrees warmer that it was in 1965. Some likely factors behind the rising water temperatures include:
- A Warming Climate: Warming water temperatures are linked to the rise in surface temperatures that have occurred over the same period.
- Land Use Changes: Surfaces like concrete, asphalt and rooftops hold more heat more than vegetated ground, making runoff from urban areas warmer than runoff from rural or forested areas. These hard surfaces also prevent water from soaking into the ground, leading to sudden discharges of warm waters into streams and rivers. Urban runoff during a summertime thunderstorm can raise a stream’s temperature by 12 degrees in less than 30 minutes.
- Loss of Trees: Fewer trees on stream banks mean that streams receive more direct sunlight, raising their temperatures.
- Thermal Power Plants: Increased demand for electricity has led to the construction of more thermal power plants over the last century, and these power plants discharge hot water.
- Dams: Dams create large bodies of standing water, which absorb more energy than running water.
Seasons: Spring, Summer, Fall
(Source: Kaushal, SS et al. “Rising stream and river temperatures in the United States.” Frontiers in Ecology and the Environment 2010; 100323112848094 DOI: 10.1890/090037.)