City's landscaping plan helps battle the heat island effect

By Craig Harvey

Many cities across the arid southwest regions of the United States are
experiencing an influx of growth as people seeking to improve their quality of life. To accommodate the increasing population, new infrastructure such as subdivisions and roads are being built in addition to the upgrades of existing roads and streets.

With all this growth, there is an increased potential for a heat island effect. This is caused when areas are developed and have significant amounts of surfaces such as asphalt or concrete with very little landscaping. These hard surfaces absorb heat during the day and retain that heat well into the night.

ISG public landscaping 5 - CopyThe result is above-average temperatures in the morning and higher than average temperatures throughout the day.

While this has not yet become an issue in Southern Utah, urban heat islands are creating climate concerns elsewhere in the desert southwest. To avoid the negative effects associated with urban heat islands, the City of St. George adopted requirements that major public streets and roads be landscaped. This strategy of landscaping can help to mitigate the heat island effect and create a more comfortable environment along with other benefits within the city.

The City has led out in a number of ways, as detailed below.

Reduced irrigation needs by selecting native and drought-tolerant plants
Water-wise landscaping designs prioritize efficient irrigation systems, such as drip irrigation or smart watering technologies, to minimize water usage. The maximum water use per drip zone (drip valve) is 12 gallons per minute (or 720 gallons per hour) and each drip zone can water up to 27 trees or 180 shrubs. Each drip zone usually waters an average of 3-4 hours per week during the active growing season (May 1st to September 1st). Grouping plants based on their water requirements ensures that each drip zone receives the appropriate amount of water, minimizing water waste and promoting sustainability.

All landscaping along the public streets and roads use water-wise landscaping (often referred to ‘xeriscaping’), which uses plants that are native to the region or plants that are adapted to arid conditions. This ensures they can thrive with minimal water requirements. Once established after about three to five years, drought-tolerant plants can have the ability to survive on limited water, making them ideal for landscaping in arid desert environments.

Not only does the city utilize efficient irrigation systems, it also strives to use secondary or re-use water sources when available for irrigation. Therefore, St. George is conserving this precious resource while still maintaining attractive public spaces.

Utilized mulching for moisture retention

While this may seem insignificant, placing mulch in planting areas is important as it helps to retain soil moisture and reduce the frequency of needed watering. This not only conserves water, but also contributes to healthier and improved soil conditions and fosters the growth of robust and resilient vegetation.

Mulching materials can include wood or organic mulch, and mineral mulches such as chat (finely crushed rock), gravel and rock cobble.

Shade creation, microclimate cooling and environmental impact

ISG public landscaping 3 - CopyPlanting trees and shrubs strategically along roadways has multiple benefits. It creates natural shade, which reduces ambient temperatures by blocking sunlight and releasing moisture through transpiration. This process contributes to the formation of cooler microclimates, offering relief from scorching heat and enhancing the comfort of outdoor spaces for pedestrians and drivers. In addition to providing shade, trees and greenery can decrease the reliance on air conditioning in nearby buildings during hot weather.

Shaded trails and sidewalks also encourage increased pedestrian usage during the day, creating a more enjoyable walking experience. The presence of trees and vegetation aids in absorbing pollutants. This leads to improved air quality, potentially reducing air pollution-related illnesses.

The results of this new approach have been pleasant.

Enhanced quality of life

Street landscaping improves the quality of life for residents, creating a more pleasant and enjoyable living environment. Access to green spaces has been linked to lower stress levels, improved mental health and an overall higher quality of life. Residents may feel happier and more content, and this often translates into a greater sense of community pride and engagement.

Improved property values

Effective street landscaping can significantly enhance property values. When street landscaping is well maintained, it adds allure to a neighborhood, making it more appealing to potential buyers or renters. Numerous studies have indicated that properties with visually appealing yards and attractive streetscapes command higher values than those with minimal or no landscaping.

The City of St. George’s use of water-wise landscapes along major public streets can help inspire residents to find better ways to landscape their property — and in the process save our most precious resource.

Craig Harvey, ASLA, is a landscape designer in the Park Planning Division of the City of St. George.