Dams and reservoirs are supposed to solve the problem of water shortages, but new research suggests their unintended effects can worsen water crises in the long run.

In a new paper published in the journal Nature Sustainability, scientists describe two phenomena, or effects, can undermine the benefits of dam and reservoir construction and expansion: the supply-demand cycle and the reservoir effect.

The first phenomena is a principle of environmental economics, whereby supply begets demand. As the water supply is increased, demand rises, putting new pressures on a finite resource. Often, water shortages motivate the expansion of reservoirs, allowing for an even larger water supply and further increased demand.

The supply-demand cycle ensures water crises get worse and worse over time, as pressure on the region's natural water supply yields increasing levels of environmental degradation.

According to the new research, the vicious cycle can "quickly offset the initial benefits of reservoirs."

The reservoir effect describes an over-reliance on a reservoir. Because an increased water supply offered by a reservoir can mask the effects of drought and water shortages, communities and governments over-reliant on reservoirs are less likely to adopt more sustainable water usage policies.

"Over-reliance on reservoirs increases vulnerability, and therefore increases the potential damage caused by droughts," researchers wrote in their paper.

According to the researchers, the reservoir effect works similarly to Gilbert White's levee effect.

"The paradox is that levees, which reduce the frequency of flooding, can increase social vulnerability to floods in two ways: by creating a sense of complacency, which can act to reduce preparedness, and by creating incentives for more human settlements in areas prone to flooding," Giuliano Di Baldassarre, researcher at the University of Uppsala, wrote in commentary accompanying the paper.

Di Baldassarre thinks the reservoir effect is even worse.

Both the supply-demand cycle and reservoir effect describe the same basic problem. Dams and reservoirs tend to encourage increased water usage, when the problem calls for the opposite solution.

Scientists hope their paper will inspire new studies into the impacts of reservoirs and dams around the world.

"In the paper we show a number of cases of the proposed supply-demand cycle and reservoir effect happening around the world, from the Maja's to Las Vegas and from Athens in Greece to Melbourne, Australia," Sally Rangecroft, from the University of Birmingham, said in a news release. "These examples reveal that a social perspective of dealing with water shortage is crucial and research on feedbacks between water and society is paramount."

In addition to more research into the interplay between hydrology, society and water infrastructure, Di Baldassarre and his colleagues call for policies that reduce water consumption.

"We suggest less reliance on large water infrastructure, such as dams and reservoirs, and more efforts in water conservation measures," Di Baldassarre wrote.

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