Xeriscape done wrong adds to Urban Heat Island

Homeowners, let’s use the completed Bureau of Reclamation hillside makeover as a cautionary tale.

It’s probably safe to assume that few are happy with the rock pile that now serves as the backdrop of our beautiful Wilbur Square Park, especially the homeowners that are now forced to overlook the unsightly hillside. And in of all places, our treasured Historic District.

In an effort to conserve water by removing all the turf, they piled rocks so high they blocked the view of the historic BOR building from all streets approaching it. But the damage is so much more than a lost view. This type of xeriscaping creates Urban Heat Island effects. By using endless tons of rocks, a heat-storing material, temperatures around the area have undoubtedly increased. A multitude of studies conclude that extreme xeriscape can increase surface and air temperatures by over five degrees. Even worse, the heat is sustained once the sun goes down, so it stays hotter longer. Worse yet, there is no shade—not a shade feature or any tree shade to be found.

The plans the BOR shared with the city (simply as a courtesy since it’s federal property) look nothing at all like the green and lush renderings they presented. Some folks I’ve spoken to express hope that over time it will grow into something more visually pleasing. Alas, desert trees, plants and shrubs are typically slow growing.

Of course, there’s a place for xeriscaping, but do it right. If you want to pull up your turf and take down trees, be mindful to plant plenty of vegetation, using a mix of moderate and low-water usage plants and trees. Consider planting more mature trees and shrubs that require light irrigation and contribute to cooling.

But again, we’re not just talking looks here.

According to starnursery.com, “In places like Southern Nevada, where we’re experiencing the Urban Heat Island effect, strategically using trees in the landscape becomes even more important. By planting more trees in the landscape, you’ll receive increased amounts of shade and the valley will experience a cooling effect as a whole. In the absence of enough urban tree canopy, experts predict that we’ll see more than 100 days a year with temperatures about 100 degrees by 2050.”

To understand the science of Urban Heat Island, we need to know about “evapotranspiration,” which is the absorption and release of water - a process that trees, plants and soil do naturally. For moisture to evaporate, it requires energy, in this case, heat energy. By using heat energy for the evaporation process, the result is cooler air—similar to how sweating cools us down. Evapotranspiration, along with the cooling effect from shade trees are majorly important factors in the fight against Urban Heat Island.

When designing a xeriscape landscape, check out the Southern Nevada Water Authority website for an extensive list of plants. There you can search for plants categorized by specific characteristics such as flower color, sun exposure, maintenance, and of course, water requirement. Star Nursery.com is another great resource for plant and tree choices. Per their website, some of the best shade tree choices that thrive in our desert are Palo Verde, Desert Willow, Mesquite trees, Southern Live Oak, African Sumac, and Shoestring Acacia—all offering large cooling canopies.

Speaking of canopies, consider adding shade sails or a permanent structural umbrella to make shade features part of your design.

Be sure to visit SNWA.com to learn about Water Smart Landscaping Rebates—“Whether you do it yourself or hire a contractor, the Southern Nevada Water Authority will rebate residential properties, businesses, HOAs and multifamily properties for grass removed and replaced with desert landscaping.”