Could These 20 Cities Run Out of Water?

By: Nick Wiltgen

Published: August 14,2013

 

 

 

 

 

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20 Cities at Risk of Water Shortages

A University of Florida study ranked 225 urban areas by water availability per capita on a proportional scale from 100 (most water) to 0.04 (least water). The next slides show the 20 cities with the least availability. (Image: A Montana water treatment plant via Flickr/USFWS Mountain-Prairie)

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  With 62 inches of rain per year, the nation’s seventh-largest freshwater lake just two counties away and the vast Atlantic Ocean in its front yard, you might think Miami is immune to water shortages.
Think again.
A 2012 study conducted at the University of Florida rated water availability and vulnerability for 225 urban areas nationwide, based on available fresh water per person. Miami ranks near the bottom of the list for water availability, and scores high on vulnerability.
Unlike many other analysis, this study incorporated both local rainfall and the availability of stored and imported water – what the authors called “hydraulic” sources. These sources include man-made reservoirs and aqueducts that can transport water from one drainage basin to another. The study also accounted for natural variability in rainfall and water availability to classify each urban area as low, medium, or high in vulnerability.
Dr. James Jawitz, professor and associate chair of environmental hydrology at the university, co-authored the study. He told weather.com there are two reasons Miami fared so poorly in the analysis.
“One is the sensitivity of ecosystems,” Jawitz said. “And the other one is because they rely on groundwater. There’s no big rivers. So there’s a decent-size aquifer, but the size of the aquifer is actually quite small and there’s not a lot of excess storage capacity.
“Luckily enough for people there, it rains regularly to keep it full, but in times of relative drought, the aquifer levels drop quickly. And there’s actually very frequent water restrictions in South Florida compared to many other parts of the country because their aquifer’s very small.”

Making The List

Dr. Julie Padowski, co-author of the study and now a post-doctoral fellow at Stanford University, emphasized that the study is a national analysis and that individual cities’ rankings are subject to some margin of error.
“We knew some information about how much water each city is using and where they are relative to these sources,” she told weather.com. She noted that by contrast, they “had no information about institutional or legal structures” governing how water is allocated.
Broadly speaking, Jawitz said that cities situated near a large water source with few other people to share it tended to ranked high on the availability list.
Topping the list is Duluth, Minn., on the shores of Lake Superior. Not only does the city sit on the shores of North America’s largest lake, but it is the only American urban area of more than 100,000 people on that lake. That means its primary water source not only is very large, but also is not shared by many other people.
It’s a different story for Chicago. It sits next to Lake Michigan – second only to Superior in terms of water volume among North American lakes. But the nearly 9 million people in its metropolitan area – and the presence of other urban areas such as Milwaukee also drawing from the lake – put Chicago in the bottom 20 nationally for water availability.
Jawitz says the issue isn’t as simple as just being near a large lake. He and Padowski had to address some basic questions in determining how to allocate water in their analysis.
“How much of that water should be allocated to people? How much should be allocated to a certain group of people, versus sharing it with other people? How much should be allocated to people versus to just leaving it in the natural system?”
“And so we take a fraction of the total amount of water in the lake and allocate it to people, and then we divide that among all the different people around that lake,” Jawitz explained.
Noting the limitations of the data available for the study, Padowski said, “There is no national policy on how to allocate” water from lakes and aquifers. “We had to come up with some general assumptions on how to allocate these resources.”
Jawitz and Padowski decided to allocate 10 percent of water in a given system to humans, but Jawitz said future research should determine what is appropriate for different situations. “There are some ecosystems where you can take more than 10 percent, and others that have already seen damage from taking as little as 10 percent,” he added.

Climate Change

Jawitz believes climate change will be an important consideration for water utilities nationwide.
“My personal view is that different regions of the country are going to have different consequences of climate change,” Jawitz said. “The southwestern United States is projected to have decreased rainfall, decreased snowpack, decreased flows in rivers like the Colorado River, and naturally decreased water availability for some of our major cities in the western United States.
“But it’s not everywhere that’s going to have decreased rainfall. Some places will have increased rainfall,” he added.
“Some places will see more water availability,” he said. “I don’t think the scientific community has a really current, robust answer as to exactly where there’s going to be increases and decreases.
“There’s a pretty strong consensus that the Southwest will have less rainfall and less water availability,” he said, adding that for most other parts of the country, the outlook is less certain.
“And then in some places like coastal Florida,” Jawitz added, “the climate change consideration [that’s] a bit more urgent is the indication of sea level rise, especially for cities that rely on coastal aquifers.” He explained that higher sea levels would potentially increase the salinity of groundwater supplies via saltwater intrusion.

Supply vs. Demand

The University of Florida study found that when stored and imported water are accounted for, fewer Americans are considered “at risk” for water shortages.
Jawitz cautioned that the study’s intent was not to dismiss the need for conservation, but rather to get a more complete picture of urban water supply.
“It’s critical to evaluate not only the naturally available water, but also the infrastructure,” he noted.
“I think that Julie and I and most water scientists are very encouraged and impressed by the past decade-or-so general trend... of decreased per-capita water consumption.”
Padowski said that demand-side water management is becoming more prevalent, noting that most of the easily-accessed water supply is “spoken for.”
“Conservation’s really important,” she said.
But she also underscored the importance of a robust water supply infrastructure. “The more redundancy you have, the more storage you have spread over a larger area, the less chance you have of running into problems.
“The cities that can do that tend to be a bit more stable.”

Interactive: Where Does Your Water Come From?

Cities across the United States get their water from a variety of sources. Our interactive map shows the primary and secondary water sources for each of the top 50 metropolitan statistical areas ranked by population from the 2010 Census. The color represents the primary type of water source for that area. When an area has multiple primary sources, a single color is chosen to represent that area.
Click or tap a dot for more information.