Water flows in the Colorado River are decreasing due to the effects of global warming, thereby increasing the risk of severe water shortages for millions of people who depend on this river, reports the Guardian.
The flow of the Colorado River has shrunk in the past few years due to droughts and high temperatures. Scientists from the US Geological Survey have published new research in Science that use a simulation to explain the physical processes behind the sensitivity of river discharge to climate warming in the Colorado basin.
Global warming has led to less snow in the Colorado River basin. Since snow reflects solar radiation from the earth’s surface ─ an effect known as albedo ─ the loss of snow decreases the reflection and so the basin absorbs more radiation from the sun. As a result, temperatures rise and so does the amount of water lost to evapotranspiration. In fact, the study estimates a 9.3% decrease in the river’s annual mean discharge per degree Celsius of warming.
The planet’s temperature has increased about 1 oC since the pre-industrial era and is heading for a 3 oC temperature rise over pre-industrial levels by the end of this century, according to the UN’s Emissions Gap Report 2019. That would lead to an increased risk of severe water shortages in the Colorado basin. The projected increase in precipitation will not be enough to offset the loss of snow, according to the study authors.
Some 40 million people rely on water from the Colorado basin. The largest reservoirs in the U.S., Lake Powell and Lake Mead, are on the Colorado River. Existing pressures on the river include intensive water use for agriculture and urban areas, as well as pollution from uranium mines. The area has suffered a 19 year drought, and last year the seven states in the basin signed a management agreement to rationalise water use.
Brad Udall, senior scientist at Colorado State University, not involved in the research, commented ‘this has important implications for water users and managers alike’. According to him the path forward is clear: ‘We’ve wasted nearly 30 years bickering over the science. The science is crystal clear – we must reduce greenhouse gas emissions immediately’.