Jon M. Hathaway

Heat and Humidity in the City: Neighborhood Heat Index Variability in a Mid-Sized City in the Southeastern United States

Daily weather conditions for an entire city are usually represented by a single weather station, often located at a nearby airport. This resolution of atmospheric data fails to recognize the microscale climatic variability associated with land use decisions across and within urban neighborhoods. This study uses heat index, a measure of the combined effects of temperature and humidity, to assess the variability of heat exposure from ten weather stations across four urban neighborhoods and two control locations (downtown and in a nearby nature center) in Knoxville, Tennessee, USA. Results suggest that trees may negate a portion of excess urban heat, but are also associated with greater humidity. As a result, the heat index of locations with more trees is significantly higher than downtown and areas with fewer trees. Trees may also reduce heat stress by shading individuals from incoming radiation, though this is not considered in this study. Greater amounts of impervious surfaces correspond with reduced evapotranspiration and greater runoff, in terms of overall mass balance, leading to a higher temperature, but lower relative humidity. Heat index and relative humidity were found to significantly vary between locations with different tree cover and neighborhood characteristics for the full study time period as well as for the top 10% of heat index days. This work demonstrates the need for high-resolution climate data and the use of additional measures beyond temperature to understand urban neighborhood exposure to extreme heat, and expresses the importance of considering vulnerability differences among residents when analyzing neighborhood-scale impacts.

Summer temperature variability across four urban neighborhoods in Knoxville, Tennessee, USA

The urban heat island (UHI) is a well-documented effect of urbanization on local climate, identified by higher temperatures compared to surrounding areas, especially at night and during the warm season. The details of a UHI are city-specific, and microclimates may even exist within a given city. Thus, investigating the spatiotemporal variability of a city’s UHI is an ongoing and critical research need. We deploy ten weather stations across Knoxville, Tennessee, to analyze the city’s UHI and its differential impacts across urban neighborhoods: two each in four neighborhoods, one in more dense tree cover and one in less dense tree cover, and one each in downtown Knoxville and Ijams Nature Center that serve as control locations. Three months of temperature data (beginning 2 July 2014) are analyzed using paired-sample t tests and a three-way analysis of variance. Major findings include the following: (1) Within a given neighborhood, tree cover helps negate daytime heat (resulting in up to 1.19 ∘C lower maximum temperature), but does not have as large of an influence on minimum temperature; (2) largest temperature differences between neighborhoods occur during the day (0.38–1.16 ∘C difference), but larger differences between neighborhoods and the downtown control occur at night (1.04–1.88 ∘C difference); (3) presiding weather (i.e., air mass type) has a significant, consistent impact on the temperature in a given city, and lacks the differential impacts found at a larger-scale in previous studies; (4) distance from city center does not impact temperature as much as land use factors. This is a preliminary step towards informing local planning with a scientific understanding of how mitigation strategies may help minimize the UHI and reduce the effects of extreme weather on public health and well-being.

Hydrologic and Water Quality Evaluation of Four Permeable Pavements in North Carolina, USA

A permeable pavement parking lot in eastern North Carolina consisting of four types of permeable pavement and standard asphalt was monitored from June 2006 to J uly 2007 for hydrologic differences in pavement surface runoff volumes, total outflow volumes, peak flow rates, and time to peak, and from January 2007 to July 2007 for water quality concentrations. The four permeable sections were pervious concrete (PC), two types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. All permeable pavements significantly and substantially reduced surface runoff volumes and peak flow rates from those of asphalt (p<0.01). Of the permeable pavements, CGP generated the greatest surface runoff volumes (p<0.01). The PICP1 and CGP cells generated significantly lower outflow volumes than all other sections evaluated (p<0.01), and had the lowest peak flows and the longest time to peak. The response of the PICP1 cell was likely due to a n increased base storage volume resulting from an elevated pipe underdrain; whereas, the CGP cell response was attributed to water retention in the sand fill layer. Overall, different permeable pavement sections performed similarly, but were substantially different from asphalt. The pH of permeable pavement subsurface drainage was higher than that of asphalt runoff (p<0.01) with the PC cell having the highest pH values (p<0.01). Permeable pavement subsurface drainage had lower NH4-N (p<0.01) and TKN concentrations than asphalt runoff and atmospheric deposition. With the exception of the CGP cell, permeable pavements had higher NO2,3-N concentrations than asphalt (p<0.01), a probable result of nitrification occurring within the permeable pavement profile. Overall, different permeable pavement sections performed similarly to one another with respect to water quality, but the CGP cell appeared to improve stormwater runoff nitrogen concentrations.

Residual indicator bacteria in autosampler tubing: a field and laboratory assessment

Microbial contamination in surface waters has become a worldwide cause for concern. As efforts are made to reduce this contamination, monitoring is integral to documenting and evaluating water quality improvements. Autosamplers are beneficial in such monitoring efforts, as large data sets can be generated with minimized effort. The extent to which autosamplers can be utilized for microbial monitoring is largely unknown due to concerns over contamination. Strict sterilization regimes for components contacting the water being sampled are difficult, and sometimes logistically implausible, when utilizing autosamplers. Field experimentation showed contamination of fecal coliform in autosamplers to be more of a concern than that of Escherichia coli. Further study in a controlled laboratory environment suggested that tubing configuration has a significant effect on residual E. coli concentrations in sampler tubing. The amount of time that passed since the last sample was collected from a given sampler (antecedent dry weather period - DWP) tubing was also a significant factor. At a DWP of 7 days, little to no contamination was found. Thus, simple protocols such as providing positive drainage of tubing between sample events and programming samplers to include rinses will reduce concerns of contamination in autosamplers.

Experiences of Urban Environmental Conditions in Socially and Economically Diverse Neighborhoods

ABSTRACT Environmental conditions can vary widely in urban areas. Temperature, green space, air quality, and other parameters may have different patterns among and within cities. These conditions may also be experienced and perceived by residents in different ways, with implications for community development and social justice in the context of environmental change. This study examines in-depth interviews (N = 20) with residents from socially and economically diverse neighborhoods to understand this variability at a more meaningful scale than typically examined in the literature. Implications for social work, community development, and multidisciplinary efforts in the pressing area of environmental change are discussed.

Temperature dynamics of stormwater runoff in Australia and the USA.

Thermal pollution of surface waters by urban stormwater runoff is an often overlooked by-product of urbanization. Elevated stream temperatures due to an influx of stormwater runoff can be detrimental to stream biota, in particular for cold water systems. However, few studies have examined temperature trends throughout storm events to determine how these thermal inputs are temporally distributed. In this study, six diverse catchments in two continents are evaluated for thermal dynamics. Summary statistics from the data showed larger catchments have lower maximum runoff temperatures, minimum runoff temperatures, and temperature variability. This reinforces the understanding that subsurface drainage infrastructure in urban catchments acts to moderate runoff temperatures. The catchments were also evaluated for the presence of a thermal first flush using two methodologies. Results showed the lack of a first flush under traditional assessment methodologies across all six catchments, supporting the results from a limited number of studies in literature. However, the time to peak temperature was not always coincident with the time to peak flow, highlighting the variability of thermal load over time. When a new first flush methodology was applied, significant differences in temperature were noted with increasing runoff depth for five of the six sites. This study is the first to identify a runoff temperature first flush, and highlights the need to carefully consider the appropriate methodology for such analyses.

Health Impacts of Extreme Weather Events: Exploring Protective Factors with a Capitals Framework

ABSTRACT Purpose: Extreme weather events are increasing with climate change. The physical and mental health of people served by social workers may be especially at risk from these hazards. This exploratory study examines if specific types of human, financial, physical, and social capital are associated with health impacts from excessive summer heat and extreme winter weather. Method: Data from resident surveys (N = 424) in low- and moderate-income areas of a Southeastern US city are analyzed with descriptive statistics and logistic regression. Results: Key findings are that health status and social cohesion are negatively associated with health impacts of summer heat and winter extremes. Conclusion: Further study is needed of how specific types of capital may help people cope with a changing climate. Social capital may be a particularly relevant area for social work to address within the pressing issue of climate, weather, and the health of vulnerable groups.

Promoting Successful Urban Watershed Restoration Through Enhanced Bioretention Cell Modelling

Urban runoff and stormwater is one of the top ten leading causes of water quality impairment in lakes, estuaries and streams in the United States (USEPA 2009). Over the last decade, bioretention systems have become a leading stormwater control measure (SCM) that contributes to the restoration of urban streams and watersheds. Bioretention cells increase infiltration of stormwater thereby reducing urban runoff volumes and peak flows which alter the hydrology of local waterways. Although these systems have proven to perform well in many site-scale field studies, less is known about how well these systems work when implemented en masse. Modelling of bioretention allows designers to scale local impacts to the larger watershed. However, current hydrologic models with bioretention capabilities consist of lumped parameters and simplifications that do not fully account for fundamental hydrologic processes. DRAINMOD is an agricultural drainage model that has shown promise when applied to bioretention systems. However, because DRAINMOD was designed for agricultural purposes, it cannot currently accommodate the rapid response time of an urban runoff hydrograph, instead aggregating data to a daily timeframe. For this study, DRAINMOD has been recoded to allow high temporal resolution inputs and outputs, more closely matching the travel times of urban systems. DRAINMOD simulations were conducted both with and without the time scale modifications (original vs. bioretention-specific model) to determine if improvements in site-scale modelling were realized. Future work will compare these results to those of simplistic, lumped-parameter bioretention modelling.

Evaluating the influence of design strategies and meteorological factors on tree transpiration in bioretention suspended pavement practices: Evaluating Tree Transpiration in Bioretention Suspended Pavement Practices

Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee, USA Department of Forestry, Wildlife and Fisheries, University of Tennessee, Knoxville, Tennessee, USA Correspondence R. Andrew Tirpak, Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN. Email: rtirpak@vols.utk.edu Funding information U.S. Forest Service, Grant/Award Number: 14‐DG‐11132540‐098; US Forest Service (USFS) National Urban and Community Forestry Advisory Council (NUCFAC)