What do you want first, the good news or the bad news?
A new study of more than 200 global cities published in the journal Global Environmental Change provided both.
"The good news is that...fewer large cities than normally reported face water stress (defined as a city using more than 40 percent of their available annual supply), when taking into account water piped in from distant watersheds," according to Adam Freed, director of Securing Water Strategy, in a blog post about the study.
Previous estimates had said around 40 percent of cities are water stressed, according to a release from The Nature Conservancy.
"The bad news is that...1 in 4 cities, accounting for more than 5 percent of global GDP, still face water stress," Freed wrote. "This is a serious challenge as more than 2 billion people will be moving into cities in the next 30 years, with regions such as Sub Saharan Africa projected to double their urban population while urban water demand quadruples."
The study illustrated its findings in dollars and cents.
"One in four cities, with $4.2 trillion in economic activity, remain in water stress. Financial limitations on infrastructure leave poor cities in greater water stress," the study said.
"Put another way, this $4.8 trillion in economic activity directly or indirectly depends on the supply of 167 billion liters of water per day (61 km3 yr−1) to these cities. Finding ways to maintain this water supply over time is thus of considerable economic importance," it said.
The results diverged from previous studies because the researchers used a different methodology.
"Previous hydrologic models that ignored infrastructure overestimated water stress," the report explained. "Our analysis shows that accounting for urban water infrastructure is essential for accurately estimating the urban population in water stress. Previous global analyses of water stress have likely overstated urban water stress because they have not accounted for this infrastructure."
Which cities are struggling the most? "The study finds that the ten largest cities under water stress are Tokyo, Delhi, Mexico City, Shanghai, Beijing, Kolkata, Karachi, Los Angeles, Rio de Janeiro and Moscow," the Nature Conservancy release said.
The researchers emphasized the urgency of this issue.
"The next few decades will be the most rapid period of urban growth in human history, with 2.6 billion additional urban dwellers expected by 2050. All these new urban dwellers will need water," the report said. "Surprisingly little is known globally about where large cities obtain their water or the implication of this infrastructure for the global hydrologic cycle."
Image credit: "LGIM0087," Sustainable sanitation © 2012, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/
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