Background: Vulnerability mapping based on vulnerability indices is a pragmatic approach for highlighting the areas in a city where people are at the greatest risk of harm from heat, but the manner in which vulnerability is conceptualized influences the results.
Objectives: We tested a generic national heat-vulnerability index, based on a 10-variable indicator framework, using data on heat-related hospitalizations in Phoenix, Arizona. We also identified potential local risk factors not included in the generic indicators.
Methods: To evaluate the accuracy of the generic index in a city-specific context, we used factor scores, derived from a factor analysis using census tract–level characteristics, as independent variables, and heat hospitalizations (with census tracts categorized as zero-, moderate-, or high-incidence) as dependent variables in a multinomial logistic regression model. We also compared the geographical differences between a vulnerability map derived from the generic index and one derived from actual heat-related hospitalizations at the census-tract scale.
Results: We found that the national-indicator framework correctly classified just over half (54%) of census tracts in Phoenix. Compared with all census tracts, high-vulnerability tracts that were misclassified by the index as zero-vulnerability tracts had higher average income and higher proportions of residents with a duration of residency < 5 years.
Conclusion: The generic indicators of vulnerability are useful, but they are sensitive to scale, measurement, and context. Decision makers need to consider the characteristics of their cities to determine how closely vulnerability maps based on generic indicators reflect actual risk of harm.
Complexities and uncertainties surrounding urbanization and climate change complicate water resource sustainability. Although research has examined various aspects of complex water systems, including uncertainties, relatively few attempts have been made to synthesize research findings in particular contexts. We fill this gap by examining the complexities, uncertainties, and decision processes for water sustainability and urban adaptation to climate change in the case study region of Phoenix, Arizona. In doing so, we integrate over a decade of research conducted by Arizona State University’s Decision Center for a Desert City (DCDC). DCDC is a boundary organization that conducts research in collaboration with policy makers, with the goal of informing decision-making under uncertainty. Our results highlight: the counterintuitive, non-linear, and competing relationships in human–environment dynamics; the myriad uncertainties in climatic, scientific, political, and other domains of knowledge and practice; and, the social learning that has occurred across science and policy spheres. Finally, we reflect on how our interdisciplinary research and boundary organization has evolved over time to enhance adaptive and sustainable governance in the face of complex system dynamics.
While there is a popular perception that Canada is a water-rich country, the Saskatchewan River basin (SRB) in Western Canada exemplifies the multiple threats to water security seen worldwide. It is Canada's major food-producing region and home to globally significant natural resource development. The SRB faces current water challenges stemming from (1) a series of extreme events, including major flood and drought events since the turn of the 21st century, (2) full allocation of existing water resources in parts of the basin, (3) rapid population growth and economic development, (4) increasing pollution, and (5) fragmented and overlapping governance that includes the provinces of Alberta, Saskatchewan, and Manitoba, various Federal and First Nations responsibilities, and international boundaries. The interplay of these factors has increased competition for water across economic sectors and among provinces, between upstream and downstream users, between environmental flows and human needs, and among people who hold different values about the meaning, ownership, and use of water. These current challenges are set in a context of significant environmental and societal change, including widespread land modification, rapid urbanization, resource exploitation, climate warming, and deep uncertainties about future water supplies. We use Sivapalan et al.'s (2012) framework of socio-hydrology to argue that the SRB's water security challenges are symptoms of dynamic and complex water systems approaching critical thresholds and tipping points. To Sivapalan et al.'s (2012) emphasis on water cycle dynamics, we add the need for governance mechanisms to manage emergent systems and translational science to link science and policy to the socio-hydrology agenda.
Vulnerability to Extreme Heat in Metropolitan Phoenix: Spatial, Temporal, and Demographic Dimensions
This study assessed the spatial distribution of vulnerability to extreme heat in 1990 and 2000 within metropolitan Phoenix based on an index of seven equally weighted measures of physical exposure and adaptive capacity. These measures were derived from spatially interpolated climate, normalized differential vegetation index, and U.S. Census data. From resulting vulnerability maps, we also analyzed population groups living in areas of high heat vulnerability. Results revealed that landscapes of heat vulnerability changed substantially in response to variations in physical and socioeconomic factors, with significant alterations to spatial distribution of vulnerability especially between eastern and western sectors of Phoenix. These changes worked to the detriment of Phoenix's Hispanic population and the elderly concentrated in urban-fringe retirement communities.
Background: Vulnerability mapping based on vulnerability indices is a pragmatic approach for highlighting the areas in a city where people are at the greatest risk of harm from heat, but the manner in which vulnerability is conceptualized influences the results.
Objectives: We tested a generic national heat-vulnerability index, based on a 10-variable indicator framework, using data on heat-related hospitalizations in Phoenix, Arizona. We also identified potential local risk factors not included in the generic indicators.
Methods: To evaluate the accuracy of the generic index in a city-specific context, we used factor scores, derived from a factor analysis using census tract–level characteristics, as independent variables, and heat hospitalizations (with census tracts categorized as zero-, moderate-, or highincidence) as dependent variables in a multinomial logistic regression model. We also compared the geographical differences between a vulnerability map derived from the generic index and one derived from actual heat-related hospitalizations at the census-tract scale.
Results: We found that the national-indicator framework correctly classified just over half (54%) of census tracts in Phoenix. Compared with all census tracts, high-vulnerability tracts that were misclassified by the index as zero-vulnerability tracts had higher average income and higher proportions of residents with a duration of residency < 5 years.
Conclusion: The generic indicators of vulnerability are useful, but they are sensitive to scale, measurement, and context. Decision makers need to consider the characteristics of their cities to determine how closely vulnerability maps based on generic indicators reflect actual risk of harm.
We investigated the spatial and temporal variation in June mean minimum temperatures for weather stations in and around metropolitan Phoenix, USA, for the period 1990 to 2004. Temperature was related to synoptic conditions, location in urban development zones (DZs), and the pace of housing construction in a 1 km buffer around fixed-point temperature stations. June is typically clear and calm, and dominated by a dry, tropical air mass with little change in minimum temperature from day to day. However, a dry, moderate weather type accounted for a large portion of the inter-annual variability in mean monthly minimum temperature. Significant temperature variation was explained by surface effects captured by the type of urban DZ, which ranged from urban core and infill sites, to desert and agricultural fringe locations, to exurban. An overall spatial urban effect, derived from the June monthly mean minimum temperature, is in the order of 2 to 4 K. The cumulative housing build-up around weather sites in the region was significant and resulted in average increases of 1.4 K per 1000 home completions, with a standard error of 0.4 K. Overall, minimum temperatures were spatially and temporally accounted for by variations in weather type, type of urban DZ (higher in core and infill), and the number of home completions over the period. Results compare favorably with the magnitude of heating by residential development cited by researchers using differing methodologies in other urban areas.
While previous studies have shown that urban heat islands (UHI) tend to increase residential water use, they have not yet analyzed the feedbacks among vegetation intensity, diurnal temperature variation, water use, and characteristics of the built environment. This study examines these feedback relationships with the help of a path model applied to spatially disaggregated data from Phoenix, Arizona. The empirical evidence from the observations in Phoenix suggests the following: (1) impervious surfaces contribute to increased residential water use by exacerbating UHI; (2) larger lots containing pools and mesic vegetation increase water demand by reducing diurnal temperature difference; and (3) smart design of urban environments needs to go beyond simplistic water body- and vegetation-based solutions for mitigating uncomfortably high temperatures and consider interactions between surface materials, land use, UHI, and water use.