Changing Landscapes, Urban Heat Island and the effects on City Water Conservation Policy

Changing Landscapes, Urban Heat Island and the effects on City Water Conservation Policy Changing Landscapes, Urban Heat Island and the effects on City Water Conservation Policy Evidence suggests that human-induced climate changes, variations, and extremes will create a warmer and drier future for the Southwestern United States and, indeed, that the turn to more intense climatic conditions has already started. In Phoenix, urban heat island (UHI) effect has increased summer nighttime temperatures by as much as 6C, consistent with some climate models. Urban vegetation as a mitigation and adaptation strategy to urban warming has been documented by extensive studies. Yet, during periods of drought, a desert city, such as Phoenix, must require consumers to reduce water use. Outdoor water uses are likely to be among the first to be targeted for reduction, which can have an enormous impact on urban greening, energy use, and food security. Without altering key urban design features, outdoor water conservation would elevate daytime warming effects and reduce or delay nighttime cooling effects during early evening hours, especially in industrial and downtown neighborhoods. According to the City of Phoenixs Water Services Department, one of the main areas in which they have an information deficiency involves outdoor water uses. With a tremendous range of landscapes and a high incidence of pool ownership, Phoenix poses unique challenges for outdoor water use. To date, national studies have focused on only a few variables, such as total turf and expected irrigation requirements using evapotranspiration rates, when analyzing water use. However, in Phoenix, where the majority of homes are partially or mostly surrounded by desert vegetation, studies must employ more sophisticated approaches to understanding how outdoor landscape types affect water use. With the future of the citys water supply being largely unknown, estimates of outdoor water use must be improved so that Phoenix can proactively prepare for drought management and water conservation while mitigating UHI effect. While water managers and planners recognize the relationship between urban vegetation and cooling, they question how much water is necessary to cool Phoenix and even whether cooling is realistic and achievable. These decision makers understand that some areas of the city are warmer or dryer than others, and that it is important to understand the customers needs concerning aesthetics, recreation, HOAs, landscape watering recommendations, and health and wellness. In this study, we will identify specific parts of Phoenix that would benefit from: (a) tree-beautification programs to decrease surface temperatures, or (b) water-conservation strategies to reduce water use. In some cases, we may need to plant additional trees, grass, and shrubs to counter UHI, but in other areas it may be more beneficial to replace high-water-using vegetation with desert adapted landscape. The goal of this proposed study is to identify areas where water use could be lowered (i.e., single family, commercial, on/off project, etc.), while considering hot-spot areas where land-surface temperatures need to be reduced by adding appropriate vegetation cover. This will allow Phoenixs City Managers to identify areas of concern and make informed decisions for effective water conservation practices across Phoenix that can lower heat stress and improve the health and wellness of city customers. The City of Phoenix has agreed to partner with the PI in the School of Geographical Sciences and Urban Planning at Arizona State University to generate a series of maps that can identify microclimate areas and to learn how different landscape patterns and composition, new developments, and redevelopment construction projects within Phoenix contribute to UHI and water conservation.