New analysis finds the southwestern US megadrought, which began in 1999, is linked to human-caused climate change. Scientists point to rising temperatures, lower precipitation and especially reduced winter snow as the drivers of the Colorado River Basin’s long-term drying. The river supplies water to seven US states and Mexico, but its natural flow should be about 16.5 million acre-feet; it is now closer to 12 million acre-feet.
Jonathan Overpeck of the University of Michigan and Brad Udall of the Colorado Water Center at Colorado State University say updated graphs in this year's Colorado River Basin report support two main conclusions: the downward precipitation trend is caused by people’s emissions, and the trend is unlikely to reverse without action on climate change. Overpeck adds that stopping climate change still requires known solutions and remains possible.
Two recent studies helped their assessment. One, led by Jeremy Klavans at the University of Colorado, Boulder, improved regional climate models. The other, led by Victoria Todd at the University of Texas at Austin, used paleoclimatology to place current temperature changes in a long-term context. The researchers warn that natural variability can still bring single wet winters, but the long-term outlook is drier. They say reservoir storage has fallen over the past 26 years and that the region is one dry winter away from severe and unprecedented water-use cuts. They also warn that unchecked warming would worsen droughts, fires and floods because climate change alters the water cycle.
Difficult words
- megadrought — a very long, severe period with little rainfall
- precipitation — water that falls from the sky, like rain or snow
- paleoclimatology — study of past climates using natural records
- emissions — gases released into the atmosphere by humans
- reservoir — a natural or artificial lake for storing water
- variability — the fact that conditions change over time
- unprecedented — never seen or experienced before
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How would reducing emissions help the Colorado River Basin, based on the article? Give reasons.
- What actions could states and communities take now to prepare for possible severe water-use cuts?
- How does studying past climates help scientists understand current drought conditions?
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