Phoenix Regional Heat and Air Quality Knowledge Repository

Problem: The prospect that urban heat island (UHI) effects and climate change may increase urban temperatures is a problem for cities that actively promote urban redevelopment and higher densities. One possible UHI mitigation strategy is to plant more trees and other irrigated vegetation to prevent daytime heat storage and facilitate nighttime cooling, but this requires water resources that are limited in a desert city like Phoenix.

Purpose: We investigated the tradeoffs between water use and nighttime cooling inherent in urban form and land use choices.

Methods: We used a Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) model to examine the variation in temperature and evaporation in 10 census tracts in Phoenix's urban core. After validating results with estimates of outdoor water use based on tract-level city water records and satellite imagery, we used the model to simulate the temperature and water use consequences of implementing three different scenarios.

Results and conclusions: We found that increasing irrigated landscaping lowers nighttime temperatures, but this relationship is not linear; the greatest reductions occur in the least vegetated neighborhoods. A ratio of the change in water use to temperature impact reached a threshold beyond which increased outdoor water use did little to ameliorate UHI effects.

Takeaway for practice: There is no one design and landscape plan capable of addressing increasing UHI and climate effects everywhere. Any one strategy will have inconsistent results if applied across all urban landscape features and may lead to an inefficient allocation of scarce water resources.

Research Support: This work was supported by the National Science Foundation (NSF) under Grant SES-0345945 (Decision Center for a Desert City) and by the City of Phoenix Water Services Department. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF.

This study addresses a classic sustainability challenge—the tradeoff between water conservation and temperature amelioration in rapidly growing cities, using Phoenix, Arizona and Portland, Oregon as case studies. An urban energy balance model— LUMPS (Local-Scale Urban Meteorological Parameterization Scheme)—is used to represent the tradeoff between outdoor water use and nighttime cooling during hot, dry summer months. Tradeoffs were characterized under three scenarios of land use change and three climate-change assumptions. Decreasing vegetation density reduced outdoor water use but sacrificed nighttime cooling. Increasing vegetated surfaces accelerated nighttime cooling, but increased outdoor water use by ~20%. Replacing impervious surfaces with buildings achieved similar improvements in nighttime cooling with minimal increases in outdoor water use; it was the most water-efficient cooling strategy. The fact that nighttime cooling rates and outdoor water use were more sensitive to land use scenarios than climate-change simulations suggested that cities can adapt to a warmer climate by manipulating land use.

Mortality from environmental heat is a significant public health problem in Maricopa County, especially because it is largely preventable. Maricopa County has conducted heat surveillance since 2006. Each year, the enhanced heat surveillance season usually begins in May and ends in October. The main goals of heat surveillance are to identify the demographic characteristics of heat-associated deaths (e.g., age and gender) and the risk factors for mortality (e.g., homelessness). Sharing this information helps community stakeholders to design interventions in an effort to prevent heat-associated deaths among vulnerable populations.

The two main sources of data for heat surveillance are: preliminary reports of death (PRODs) from the Office of the Medical Examiner (OME) and death certificates from the MCDPH Office of Vital Registration.

Heat-associated deaths are classified as heat-caused or heat related. Heat-caused deaths are those in which environmental heat was directly involved in the sequence of conditions causing deaths. Heat-related deaths are those in which environmental heat contributed to the deaths but was not in the sequence of conditions causing these deaths. For more information on how heat-associated deaths are classified, see the definitions in Appendix. For more information on MCDPH’s surveillance system, see Background and Methodology.

Maricopa County experiences extreme heat, which has adverse effects on community health and has been recognized as a serious public health issue. Therefore, the Maricopa County Department of Public Health (MCDPH) has conducted surveillance activities to assess morbidity and mortality due to extreme heat for the past 10 years. In 2016, MCDPH was interested in expanding their scope to include other climate-sensitive public health hazards. Subsequently, a network of stakeholders with an interest in the health effects of climate-sensitive hazards was established as the Bridging Climate Change and Public Health (BCCPH) stakeholder group. A smaller Strategic Planning Workgroup of key stakeholders from the BCCPH group was then convened over three sessions to work on a strategic plan for the group, which culminated in this document.

Practical Vision
The driving discussion question to identify the Strategic Planning Workgroup’s practical vision was, “What do we want to see in place in the next 3-5 years as a result of our actions?” The goal of this question was to help the group develop concrete outcomes that the BCCPH workgroup would like to achieve through activities included in the strategic plan. The following goals were identified:
 A healthy community infrastructure design
 Reframed messaging for multiple stakeholder needs
 A coordinated multi-scale education effort
 Improved health strategies and outcomes
 A diverse network of partnerships for climate change adaptation and mitigation planning and development
 New funding opportunities
 Policy and research strategies, and private sector engagement.

Underlying Contradictions
The driving discussion question to identify underlying contradictions was, “What is blocking us from moving towards our practical vision?” The following challenges were identified:
 People act out of self-interest vs. common good
 Siloed effects lead to poor coordination
 Political partisanship delays unified action
 Conflicting information leads to biases
 Culture and convenience impacts action
 Vulnerable populations not represented, and normalization of climate change related negative effects

Strategic Directions
During the BCCPH Strategic Planning Workgroup meetings, participants identified five strategic directions for addressing environmental concerns affecting the health and well-being of the community. These strategic directions are in agreement with the climate and health adaptation strategies outlined in the Arizona Climate and Health Adaptation Plan. The strategic directions for Maricopa County are:
 Fostering Environmental Action for a Healthier Community
 Coordinating Research and Collaborative Efforts to Catalyze Change
 Developing a Strategic and Targeted Communication Plan
 Promoting Community Awareness and Public Education about Climate and Health
 Celebrating Success and Champions