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.
The COVID-19 pandemic has renewed interest in the importance of indoor air quality for health. The spread of respiratory aerosols is the primary mechanism for COVID-19 transmission, making it crucial to understand the role of effective ventilation in managing the risk of disease transmission. The concentration of exhaled carbon dioxide (CO2) in indoor spaces can be used as a proxy measure of ventilation efficiency. Poor indoor air quality has been associated with a range of acute and chronic health problems, including respiratory issues, cardiovascular disease, and cancer. Poor air quality may also impair cognitive performance and productivity. Social and economic inequalities exacerbate the impact of indoor air quality issues, making it crucial to address these problems in an equitable manner. Public libraries have been identified as an effective intermediary for providing education and free air quality monitoring technology to communities, with the ultimate goal of promoting awareness and increasing access to tools to promote accountability for maintaining high indoor air quality standards. The primary objectives of this initiative are to: 1) develop a citizen science toolkit for assessing indoor air quality in public spaces and deploy the toolkit to public libraries in Arizona; and 2) to conduct a program evaluation to determine whether this kit can be effectively deployed through public libraries to promote citizen science efforts and engage community members in promoting healthier indoor air quality, identify areas where improvements can be made, and prepare the program to be scaled to a larger audience.