Is an “oasis” landscape perfect for Denver and arid climates?

The term and technique of xeriscaping was invented by Denver Water for the high desert, but it has often been a difficult aesthetic sale among consumers. Some thought of it as “zeroscaping” – as in zero appeal – and were not impressed with how much landscaping water desert-style projects could save in their home backyards.

But the inhabitants of the cities and suburbs of the Front Range are starting to realize that the days of the boundless expanses of green and unquenchable meadows are over. They suck up too much water from the Colorado River and are outlawed in some large cities, such as Aurora.

So is an “oasis” home landscape the right solution for both water use and city climate comfort?

A new study from the Desert Research Institute and scientists from two Western universities seem to think so. The researchers compared both water use and air temperature at three different landscape levels: mesic, or traditional turf surrounding thirsty trees; what they call xeric, a barren landscape featuring drop-fed desert plants surrounded by dry rock or mulch; and a middle ground, an oasis, where shade trees or shrubs and small grassy islands interrupt a drier and more resource-friendly landscape.

Play areas and facilities give a nod to a more natural landscape within High Prairie Park. (Kathryn Scott, Special for The Colorado Sun)

The study of several scenes around Phoenix found that the oasis style could be a winning compromise for arid urban climates such as those of Arizona, Colorado, Nevada and Southern California. The oasis uses far less water than grass lawns and still keeps the ambient temperature within the comfort range produced by the shadier, greener turf.

According to the study, published in the journal Hydrology, air temperatures in xeriscape textures averaged 5.4 degrees higher than those in the oasis or mesic style of the turf.

Researcher Rubab Saher of DRI’s Department of Hydrological Sciences says this “best of both worlds” effect is the key to convincing the public, developers and urban planners to follow the oasis style: they need to be sure that a design Water-sized won’t worsen urban “heat islands” that can make the less thoughtful subway sections of Denver, Las Vegas, or Phoenix a daytime hell.

Furthermore, the oasis designs are only more pleasing to the eyes of many residents.

“Removing turf grass from the landscape is an excellent approach to saving water, but if we remove all turf grass, the temperature will rise,” Saher said. “For every acre of grass removed, we also need to plant native and / or rainy trees to make arid cities livable in the long term.”

Water analysts praised the report and cited both the number of metropolitan areas cutting the turf and the plethora of places in Colorado that are demonstrating oasis techniques on the ground.

“There is growing momentum in the past year as well,” said Lindsay Rogers, a water analyst at the nonprofit Western Resource Advocates. “I am glad that these institutions are trying to gain a better understanding of landscape materials that could reduce or exacerbate the urban heat island effect, because this is a critical issue when it comes to good landscaping practices with regards to water, and a quantity comes out. ”

Rogers would like to see the same scientific study of Colorado city environments to measure whether field practices produce lower temperatures than similar projects in Arizona or Nevada. Colorado landscapers tend to use more wood-based mulch than rock to replace large grassy areas, and wonders if those different materials would change heat island measurements.

Colorado developers and water researchers are demonstrating various levels of the oasis style up and down the Front Range in an encouraging demonstration of drought and climate adaptation, Rogers said.

Aurora’s Painted Prairie residential complex is building water savings in its public parks and construction sites. Northern Water, which supplies dozens of communities in the North Front Range, has a series of demonstration gardens at its Berthoud location. Denver Botanic Gardens, Colorado State University, and others are also experimenting with blends of plants and materials that can save water by cooling the landscape, he said.

The finished houses and those still under construction form the backdrop to the raised flower beds within Columbine Gardens. (Kathryn Scott, Special for The Colorado Sun)

Meanwhile, cities that discourage traditional sidewalk-to-sidewalk turf are also trying to encourage alternatives to the southwestern desert-style landscape that has given xeriscaping a bad reputation.

“We’re seeing many of our cities include parameters in their turf replacement programs that recognize the benefits of living plant materials, from lowering temperatures to creating more pollinator and shade habitats,” Rogers said. This can include a minimal percentage of live plant materials or a minimal number of trees.

“They are really trying to balance the need to reduce water use in the landscape with all those other essential benefits that our landscapes have to provide,” he said.

The Desert Research Institute study, with coauthors from Arizona State University and the University of Nevada Las Vegas, also looked at the impact of the landscape on nighttime temperatures and even whether the placement of buildings or homes causes their own climate effect. .

The middle oasis style, while cooler by day, didn’t show cooler temperatures than xeriscaping at night, Saher said. The oasis design doesn’t cool down as fast at night as a more traditional green lawn. They cannot fully explain why that would be true.

And it appears that the placement of the building can create cooling effects similar to grassy lawns through the strategic orientation of the shadow produced by the structures.

Saher says his next project will be about comparing official irrigation recommendations from the increasingly stingy Southern Nevada Water Authority with how residents are actually watering their lawns.

“To see how far we are or how close we are,” he said.

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