How using “oasis” models can combat drought and the effect of urban heat

This story is part of a series on how Las Vegas is coping with its water shortage and what Utah can learn from its efforts. Click to learn more: Part 1, Part 2, Part 2 – Sidebar.

Removing all water-intensive plants isn’t the panacea in times of rising temperatures and droughts in the Southwest, according to a new study.

The deadly flooding of Pakistan’s Indus River in 2010 and a heat wave five years later are the two events that motivated Rubab Saher, who has a PhD in civil and environmental engineering, to study urban climates.

“You know, these things keep happening every five to 10 years, but shame on you for not having better ideas and better infrastructure,” Saher said. “Unless it’s fixed in every city, I don’t think my motivation will dry up.”

Saher is a Pakistani native from Sindh district to Halas. She came to the United States in 2016 for a semester as a researcher at the US Pakistan Center For Advanced Studies in Water at the University of Utah in Salt Lake City.

Working with like-minded researchers at the center, she said she no longer felt like a “geek” and went on to earn her doctorate from the University of Nevada at Las Vegas. She is now working on solutions for climate impacts in urban areas, balancing wishes with reality as communities heat up.

In the midst of a decades-long drought, cities in the American Southwest are looking for ways to reduce water usage. Las Vegas, a city notorious for excess, has built a new reputation for itself as one of the most water-efficient cities in the world. The city is recycling most of its internal water, and its ban on non-functional grass is the first law of its kind in the nation.

The average rainfall in this Mojave Desert is 4.2 inches annually. Water is in short supply, and sprinkler-watered lawns take up too much of the city’s drinking water supply. One square foot of grass requires 78 gallons of water per year. The average drip-irrigated landscape uses much less, about 13 gallons per square foot per year. However, what types of plants the turf is replaced with matters. Much.

Some landscapes can contribute to the “urban heat island effect” where afternoon temperatures in cities, large and small, tend to get 15-20 degrees warmer than surrounding rural landscapes due to the plethora of radiating pavement and asphalt heat. Cooling cities could save lives. The National Institutes of Health reported this year that extreme heat was related to an increase in the number of deaths in the United States between 2008 and 2017.

As a postdoctoral research associate at the Desert Research Institute (DRI), Saher led a study this year published in the journal Hydrology looking at common arid landscapes and how they affect temperature. Scientists analyzed three types of sites in Phoenix consisting of low to high water use:

  • Xeric, desert plants that require minimal water

  • Oasis, a mix of desert and water-intensive plants

  • Mesic, a site with trees and grassy meadows with water-intensive plants

“And then we estimated surface temperatures, evaporation rates and irrigation water needs for these three landscapes,” Saher said.

They also measured air temperature and wind speed. Saher said the results were unexpected. The oasis landscaping has provided the best long-term result for both water saving and cooling. It showed 35.6 degrees more daytime cooling than mesic.

“So this split personality of … saving water for the oasis because the oasis has less water than the mesic, while also contributing to daytime cooling, was a pleasant surprise.”

So even though the mesic site had cooler air and surface temperatures overall, it required more water and the xeric site was simply too hot. Drought-tolerant plants retain water, limiting the cooling effect on their surroundings. Air temperatures measured 5.40 degrees higher than the other two landscapes.

Oasis were Goldilocks. Saher said this landscaping requires light drip irrigation and contributes to cooling through plant evapotranspiration. Examples of canopy trees in the oasis, he said, include Acacia, ghost gum, or shrubs like dwarf poinciana.

Saher suggests something in between in the garden—that sweet spot where some lush plants grow—weather tree and native shrubs can actually freshen things up and save water in the long run.

Las Vegas mitigates the “urban heat island effect” with some landscaping requirements. According to Bronson Mack, a spokesman for the Southern Nevada Water Authority, areas converted from grass must include at least 50 percent canopy coverage.

“This was a trend that was happening as our community developed and long before we implemented a turf conversion program,” Mack said.

Since it’s the desert, Mack said they don’t have much of a native plant palette, so they look to Utah for some of the state’s native species.

“Especially those that are flowering plants, there is benefit for the bees, the hummingbirds, the pollinators of the world. It’s actually a more efficient and more oxygen-producing plant choice than grass, especially when you consider the amount of fossil fuels that grass requires. You have to consider that all the water used by the grass has to be pumped and delivered, which consumes energy and energy.

Utah is the second driest state in the nation, just behind Nevada. Utah has a lot to make up for if the state is to match the water conservation feats of southern Nevada. As efforts mount to conserve water in Utah by abandoning the glut of meadows, Shaun Moser, Conservation Park director of the Jordan Valley Water Conservancy District, urges caution.

“Some people think the solution is to rip up all the lawn and put nothing but rock and no plants,” Moser said. “I see it as an overreaction and an overcorrection in my mind. If we do that, I think you’ll start to see problems with the urban heat island effect, maybe our electric bills will start to go up a bit just because rock doesn’t breathe like grass.

Utah’s meadows and landscapes absorb much of the state’s drinking water, about 50 to 70 percent. To use less and still freshen up, Moser suggests something like the district’s Localscapes that cuts water usage by up to 66 percent.

“Most of the time, if someone installs a Localscape, they put the front and back lawn, but it’s only 20% to 30% of the landscaped area,” he said. “And the other part is the patios and vegetable gardens and flower beds with trees and shrubs, so it’s more of a balanced landscape that conserves water at the same time.”

For those grass reserves, he said he’s seeing a trend toward warm-season types like Buffalo and Blue grama that tend to use less water than common Kentucky bluegrass.

“They’re dormant in spring and fall, so that’s the tradeoff.”

A couple of native plants he said to consider are the Bigtooth maple tree and the western Sundancer daisy, a small perennial flower. One non-native tree she recommends is a hybrid elm type that includes Frontier, Homestead, and Accolade.

“These are plants that do really well in our environment here in Utah and grow fast and give you shade quickly and don’t use a lot of water,” Moser said.

The 100-acre Utah State University Botanical Center in Kaysville is doing its part. He reduced his water usage by 75 percent in two years just by watering less and putting plants into “survival mode,” said manager Jerry Goodspeed.

“We realized that many plants are doing well, to our surprise,” he said. “Learning as we go.”

He said the center has a program called Sego Supreme in which it is trying to develop and promote perennials that don’t require a lot of water. In partnership with Colorado State University, look for these native flowers in the foothills.

“It’s kind of a win/win situation, where we don’t have to see that plant you grew up with, the water plants of English cottage gardens, the water-loving perennials,” she said.

Goodspeed said he can see the benefits of an oasis-like landscape that is water and cooling wise, and also reduces carbon dioxide. And he doesn’t mind a little weed, but not too much.

“We’re off a strange tangent of lush grass and plants,” Goodspeed said. “There’s a balance, folks, and we need to swing that pendulum back and remember we live in a desert.”

This article is published through the Great Salt Lake Collaborative, a solutions journalism initiative that partners with news, education and media organizations to help educate people about the plight of the Great Salt Lake and what can be done to make it better. difference before it’s too late. Read all our stories on greatsaltlakenews.org

    .

Leave a Reply

%d bloggers like this: