More rain due to climate change might not mean more water resources

A new study explains this paradox.

As severe drought grips parts of the Western United States, a below average flow of water is expected to enter Lake Powell and Lake Mead, the two biggest reservoirs of the Colorado River Basin. (Credit: Justin Sullivan/Getty Images)
As severe drought grips parts of the Western United States, a below average flow of water is expected to enter Lake Powell and Lake Mead, the two biggest reservoirs of the Colorado River Basin. (Credit: Justin Sullivan/Getty Images)

As the impacts of climate change continued to intensify this year, much of the country experienced record levels of rainfall — so much that 2018 has already been deemed the fifth-wettest year on record in the contiguous United States.

Despite climate change making some places much wetter, however, global water resources are in decline. This is the paradoxical finding of a new study published in the journal Water Resources Research.

As temperatures rise, warmer air is able to hold more moisture, making rainfall more intense in areas such as Washington, D.C., Maryland, North Carolina, and Philadelphia.

Yet, at the same time, climate change is exacerbating drought conditions in other areas, which makes the ground drier; according to scientists, increasingly dry soil leads to less water entering vital freshwater resources.


Analyzing data from 43,000 rainfall stations and 5,300 river monitoring sites in 160 countries, the study is being call the “most exhaustive” of its kind. Based on this research, scientists found that for every 100 raindrops that fall on land, only 36 are considered “blue water” — meaning rain that enters rivers, lakes, and aquifers. The rest is retained as soil moisture — “green water” — which is used by increasingly thirsty landscapes and ecosystems.

Essentially, as more rainfall is being absorbed by the land, there is less that runs off into rivers, and therefore less available for human use.

Until now, the impact of dry soil on water resources “is something that has been missed,” by scientists said Ashish Sharma, the study’s lead author and a fellow at University of New South Wales.

“We expected rainfall to increase, since warmer air stores more moisture — and that is what climate models predicted too,” Sharma said in a statement. “What we did not expect is that, despite all the extra rain everywhere in the world, is that the large rivers are drying out.”

In the U.S., for instance, the Colorado River, which supplies water to 40 million people in several states, is in the midst of an ongoing 19-year drought. The river draws water from Lake Mead, which is currently experiencing water levels so low it could trigger a first-ever official shortage on the river. Officials from California, Arizona, and Nevada are trying to come to agreement on a drought contingency plan in order to avoid a major crisis.


“Less water into our rivers means less water for cities and farms,” Sharma said. “And drier soils means farmers need more water to grow the same crops. Worse, this pattern is repeated all over the world, assuming serious proportions in places that were already dry. It is extremely concerning.”

At the same time, major new reports from the U.N. Intergovernmental Panel on Climate Change (IPCC) and the U.S. National Climate Assessment warn that climate change will bring more intense storms and rainfall. This in turn will cause challenges for cities facing more flooding with aging infrastructure.

The new rainfall study, however, does offer up a few solutions.

“One option is to wait for international agreements to take effect, so greenhouse gas concentrations can be reined in — but this will take a long time. The other option is to be proactive, and re-engineer our water systems so we can better adapt and cope,” said Sharma.

To do this, new policies and infrastructure is needed. Around the world, water-intensive farming, for instance, must be shifted to use more efficient techniques. At the same time, water reservoirs will need to be expanded.

“There are no silver bullets,” warned Sharma. “Any large-scale re-engineering project will require significant investment, but the cost of inaction could be monstrous.”


This was echoed by Mark Hoffman, dean of engineering at UNSW, who called for a global conversation to discuss how to deal with this “unfolding scenario.”

While there’s no easy fix, he said, that doesn’t preclude societies taking preparations to address the issue.

“Climate change keeps delivering us unpleasant surprises,” he said in a statement. “Nevertheless, as engineers, our role is to identify the problem and develop solutions. Knowing the problem is often half the battle, and this study has definitely identified some major ones.”