You can still have an ‘oasis’ in the desert

Removing all water-intensive plants is no panacea in times of rising temperatures and drought in the Southwest, a new study has found.

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

“You know, these things keep happening every five or 10 years, but shame on us for not coming up with better ideas and better infrastructure,” Saher said. Unless it’s resolved in every city, I don’t think my motivation dries up.

Saher hails from Pakistan from Sindh district in Halas. She came to the United States in 2016 for a semester as a researcher at the Pakistan Center for Advanced Water Studies 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 “misfit” and went on to earn her doctorate at the University of Nevada, Las Vegas. Now she’s working on solutions to climate impacts in urban areas, trying to balance wishful thinking with reality as communities heat up.

Amid a decades-long drought, cities in the American Southwest are looking for ways to reduce their water usage. Las Vegas, a city known for its excesses, has earned a new reputation as one of the most water-efficient cities in the world. The city recycles most of its indoor water, and its non-functional grass ban is the first law of its kind in the nation.

The average rainfall in this Mojave Desert is 4.2 inches per year. Water is scarce and sprinklered lawns consume too much of the city’s drinking water. One square foot of grass requires 78 gallons of water per year – that’s a 10 foot high water column. Drip-irrigated landscaping uses much less on average, about 13 gallons per square foot per year. However, what types of plants the turf is replaced with questions. A lot.

Some landscapes can contribute to the “urban heat island effect” in which afternoon temperatures in cities large and small tend to be 15 to 20 degrees warmer than the surrounding rural landscapes due to the plethora of pavement and asphalt radiating heat. Cooling cities could save lives. The National Institutes of Health reported this year that extreme heat is linked 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, Saher this year led a study published in the journal Hydrology looking at common arid landscapes and how they affect temperature. Scientists analyzed three types of sites in Phoenix, characterized by low to high water consumption:

• Desert xeric plants that require minimal water
• Oasis, a mixture of desert and water-intensive plants
• Mesic, a wooded and grassy site with water-hungry plants

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

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

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

So even though the mesic site had the coldest air and surface temperatures overall, it required the most water, and the xeric site was just too hot. Drought-resistant plants retain water, limiting the cooling effect on their environment. Air temperatures were 5.4 degrees warmer than in the other two landscapes.

Oasis was Goldilocks. Saher said this landscape requires light drip irrigation and contributes to plant evapotranspiration cooling. She said an example of canopy trees in the oasis include acacia, ghost gum or shrubs like dwarf poinciana.

Saher suggests a middle ground in the garden — that sweet spot where a few lush plants, a rain tree, and native shrubs can actually cool things down and save water in the long run.

Las Vegas mitigates the urban heat island effect with certain landscaping requirements. According to Bronson Mack, spokesperson for the Southern Nevada Water Authority, areas converted from grass must include at least 50% canopy cover.

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

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

“Especially those that are flowering plants, there are benefits for bees, hummingbirds, the pollinators of the world. It’s actually a more efficient, more oxygen-producing plant choice than going with grass, especially considering how much fossil fuel it takes for that grass.You have to consider all the water the grass uses to be pumped and delivered, which consumes energy and electricity.

Utah is the second driest state in the country, just behind Nevada. And Utah has a lot of catching up to do if the state is to match Southern Nevada’s water conservation feats. As efforts intensify to conserve water in Utah by ditching the glut of lawns, Jordan Valley Water Conservancy district park manager Shaun Moser urges caution.

“Some people think the solution is to rip out the whole lawn and just put in rock and no plants,” Moser said. “I see it as an overreaction and 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 sweat like lawn .

Utah’s lawns and landscapes suck up a large portion of the state’s drinking water, about 50% to 70%. To use less and still be fresh, Moser suggests something like District’s Localscapes which reduces water usage by up to 66%.

“Most of the time if someone puts a Localscape in, they put grass in front and behind, but that’s only 20% to 30% of the area of ​​the landscape. And the other part is patios and lawns. 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 resistant to grass, he said he sees a trend toward warm season types such as Buffalo and Blue grama which tend to use less water than Kentucky common bluegrass.

“They go dormant in spring and fall, so that’s the trade-off.”

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

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

Utah State University’s 100-acre botanical center in Kaysville is doing its part. He cut his water use by 75% over two years by simply watering less and putting his plants in “survival mode,” said manager Jerry Goodspeed.

“We realized that a lot of plants are doing very well, much to our surprise. … learn as you go.

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

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

Goodspeed said he can see the benefits of an oasis-like landscape that is water efficient and refreshing, and also reduces carbon dioxide. And he doesn’t mind a little grass in it – but not too much.

“We’re way off on a weird tangent of grass and succulents,” Goodspeed said. “There’s a balance, people, and we have to turn that pendulum back and remember that we live in a desert.”

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