Mitigating Urban Heat: How the Use of Greywater Can Mitigate the Urban Heat Island Effect

Urban heat island effect is caused by the built environment and impervious surfaces in urban areas causing the local air temperature to be significantly higher than that of near-by rural areas. This effect continues to worsen and spread nationwide as urban sprawl increases through land development. As more land gets paved over, more heat energy is produced and radiated into the local atmosphere. In Phoenix, urban heat island effect is expected to be the most prominent when the city has been the fastest growing metro area in the United States in this decade and continues to grow at a rapid pace. As urban heat island effects increase, climate change caused by anthropogenic activities continues to worsen. This causes drought conditions to worsen all across the American Southwest. California was the first state to enact water restrictions in response to the current drought conditions in 2015, with Nevada and Colorado following in 2021 in efforts to preserve water. Sustainable urban water systems management and design have been an emerging research area. One of the most effective systems being the reuse of greywater in irrigation. With this use of greywater for all outdoor water needs, excluding swimming pools, there is the ability to use equal amounts of outdoor water as indoor water. This increases the amount of available water for all landscaping. With increased amounts of available water, plants and vegetation will most often grow fast and larger. Larger and healthier vegetation both increase shade as well as evaporative-transpiration. Both of these can decrease the local air temperature. This research aims to investigate if and how the reuse of greywater for landscape irrigation can ultimately lead to cooler air temperatures, decreasing the urban heat island effect. In Spring 2022, I partnered with a local landscape architecture firm to examine a case study of a pilot greywater reuse system. The pilot was the basis for a larger greywater reuse system integrated into a multifamily apartment complex, currently under construction, in downtown Phoenix.