�¼������ϲ�

Extreme heat in �¼������ϲ� isn’t a new phenomenon, but recent trends - including Phoenix  reaching at least 100-degree temperatures - have reinforced the need to proactively plan for increasingly hot temperatures on a nearly year-round basis. Given the ongoing heat and water crises, researchers at �¼������ϲ�’s public universities set out to discover how urban tree watering strategies can be improved to reduce water needs and the urban heat island effect while remaining scalable and efficient.

With support from an �¼������ϲ� Board of Regents’ Research Grant, researchers at the University of �¼������ϲ� and �¼������ϲ� State University explored this question and tested new and existing water conservation practices. The results have successfully pushed the limits of current water conservation efforts and gained national attention for their potential to address longstanding challenges in �¼������ϲ� and across the globe.  

Smart tree watering techniques lead to a reduction in water use by as much as 60 percent when compared with current water use in Tucson’s public lands, such as parks and right-of-way, according to preliminary research findings from the grant, Smart Tree Watering in �¼������ϲ�’s Urban Environment. Working with 80 tree saplings at the �¼������ϲ� Experiment Station’s Campus Agricultural Center, the student and faculty research team projected that 1,700 gallons of water could be saved per year, per tree through these early stages of tree establishment. 

“We have water scarcity, but we need more water to grow these trees,” said Bo Yang, U of A professor of Landscape Architecture and Urban Planning. “Smart tree watering techniques we’re comparing are scalable, economic and cost effective for cities and individuals. This hasn’t ever been studied at this scale; We can make the trees thrive and survive.”

Working with the City of Tucson’s Urban Forestry and Storm to Shade programs, the Department of Transportation and Mobility, and the City of Tempe’s Community Services Department on an advisory basis, researchers say this project is particularly beneficial for climate resiliency in cities where planting trees can be an antidote to warming temperatures. Nationwide, landscape irrigation  of all residential water. By cutting water use in half, municipalities could realize economic benefits, conserve water, and create more cooling shade for residents. 

As part of the research, four species – Desert Willow, Hackberry, Ironwood, and Joan Lionetti Live Oak – are paired with four smart watering techniques in the research project, including rainwater harvesting, organic mulch, plastic-based hydrogel, and cellulose-based hydrogel. (Hydrogels can absorb water up to 500 times their weight in water and are a cost-effective way to concentrate water along tree roots.) 

Testing slow water practices to quantify impacts on soil health and tree growth showed that experimental treatments maintained 22-37% higher soil moisture content compared to conventional drip irrigation planting. 

“Water conservation is a crucial aspect of maintaining �¼������ϲ�’s infrastructure and livability, particularly as we endure the ongoing effects of drought and climate change. Coalescing research efforts among our universities to address critical statewide challenges such as water scarcity and urban heat benefits our communities and the well-being of all �¼������ϲ�ns,” said �¼������ϲ� Chair Cecilia Mata. “I’m proud of the innovative spirit and excellent research that has been accomplished through the Regents’ Research Grant.”

As a result of their findings, the research team, including students Annalise Hummel, Christian Aguilar Murrieta, and Cordell Lee along with faculty advisors Bo Yang, Vanessa Buzzard, Grant McCormick, Shujuan Li, Douglas Loy, Zhihua Wang, and Tianfang Xu, were selected for an  in the research category by the American Society of Landscape Architects, the highest level of award in this field. The team will accept their award at an official ceremony taking place this October in Washington, D.C. at the Conference of Landscape Architecture. 

The research team will broadly disseminate findings through workshops that will engage municipalities, counties and community groups. Research team members at ASU will also utilize artificial intelligence and machine learning models to demonstrate how these smart irrigation techniques can be applied at scale to further benefit water savings and heat mitigation in �¼������ϲ�’s urban environment and ultimately inform water use policy and guidelines. 

According to Zhihua Wang, associate professor in the School of Sustainable Engineering and the Built Environment at ASU, “The team employed a state-of-the-art urban land surface model named �¼������ϲ� Single Layer Urban Canopy Model (ASLUM), and machine learning algorithms to quantify and optimize the water saving efficiency of smart watering technology, scaled up to the City of Tucson and Phoenix Metropolitan Area.” 

The �¼������ϲ� Board of Regents’ Research Grants fund research to address and deliver solutions to critical issues facing the state of �¼������ϲ� and its citizens. The board funds these grants with Technology and Research Initiatives Fund (TRIF) revenue, bringing together university experts to work with state agencies to address important issues for the state.

The full Smart Tree Watering project team and acknowledgements include: 

• Faculty advisors:
  • U of A: Bo Yang, Vanessa Buzzard, Grant McCormick, Shujuan Li, Douglas Loy
  • ASU: Zhihua Wang, Tianfang Xu
• Student team: 
  • U of A: Annalise Hummel, Christian Aguilar Murrieta, Cordell Lee
• Acknowledgements:
  • LoriAnne Barnett Warren, Cori Dolan, �¼������ϲ� Department of Forestry and Fire Management
  • Kenneth Polasko, �¼������ϲ� Board of Regents