The Utah Division of Water Resources warned that the popular trend of replacing greenery with rock-heavy "zeroscapes" may inadvertently increase neighborhood temperatures and drive up water evaporation. While intended to conserve water, these gravel-heavy landscapes can contribute to the urban heat island effect, potentially making communities hotter and drier.
Ecological Costs of Rock Gardens
The Division of Water Resources noted that nearly 60% of residential water use in Utah is dedicated to landscaping, making it the single largest opportunity for individual water conservation. However, the agency cautioned that substituting plants with gravel is not always an environmental victory, as it can create significant ecological gaps.
According to the Division, eliminating plants removes essential ecosystem services. Beyond aesthetics, vegetation plays a critical role in supporting native pollinators, feeding local wildlife, maintaining soil health, and preventing erosion. Additionally, plants serve as carbon sinks and provide natural cooling for neighborhoods through evapotranspiration.
Rising Urban Temperatures
A primary concern with zeroscape designs is their contribution to the urban heat island effect. According to the Environmental Protection Agency (EPA), heat islands are urban areas that experience higher temperatures than their rural surroundings.
These temperature spikes occur because materials like concrete, asphalt, and rock soak up solar energy during the day and radiate that heat throughout the night. This phenomenon can make cities feel like ovens and prevents nighttime cooling. The Utah Climate Center has identified Salt Lake City as one of the top three urban heat island cities in the United States.
The Evaporation Cycle
The heat generated by rock-heavy landscapes creates a secondary water problem: increased evaporation. As surfaces heat up, the surrounding air and soil lose moisture more rapidly.
The Division of Water Resources explained that even if a zeroscape uses less water directly, the resulting heat can cause nearby landscapes to require more water to survive. This creates a cycle where efforts to save water in one yard may lead to increased water consumption in another due to the heightened heat and evaporation rates.
Strategies for Waterwise Cooling
To combat the heat island effect, the Division recommends using shade as a "secret weapon." The most effective method is keeping sunlight off heat-absorbing surfaces like brick, asphalt, and rock. This can be achieved through the use of tall, leafy trees, climbing vines on fences, large shrubs, and perennials.
For ground cover, the agency suggests using shredded bark mulch in areas where it will not blow or wash away. The low density of mulch helps prevent heat retention. If homeowners do choose to use rocks, the Division advises selecting lighter colors and avoiding black stones to minimize heat absorption.
Sustainable Landscaping Solutions
The Division of Water Resources encourages Utahns to adopt "Localscape Principles" to create yards that save water while supporting the local environment. This approach focuses on working with nature rather than against it.
Practical tips for residents include keeping only as much lawn as is actually used, adding drip irrigation to planting and vegetable beds, and using rotors for efficient grass watering. The agency also noted that projects qualifying for the Landscape Incentive Program must include at least 50% plant coverage at maturity.
Achieving Environmental Balance
While the Utah Division of Water Resources supports the effort to save water, the emphasis remains on balance. By prioritizing plants and shade over gravel, residents can help mitigate the rising temperatures in Utah's urban and suburban spaces.
