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Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR
International Journal of Climatology
Abstract
Changes in land use and land cover alter the local energy balance and contribute to distinct urban climates. This paper presents a local-scale above-canopy study of intra-urban land cover mixes in two cities to analyse the relative effects of surface morphology and local climate on the surface energy balance (SEB). The study is conducted for urban areas in Phoenix, Arizona, and Portland, Oregon, cities with distinct climates but similarly warm and dry summers. A Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) is used to analyse the relative contributions of local weather extremes and land cover variations on the urban energy balance. The partitioning of net all-wave radiation into turbulent sensible and latent heat fluxes as well as heat storage is investigated for a typical dry summer month and two extreme weather scenarios in the two cities. Results of sensitivity analyses show that incoming solar radiation is an important driver of the SEB in LUMPS and should be considered in the generation of climate scenarios. The relationship between individual land cover fractions and SEB fluxes is not clear because of interrelated effects of surface characteristics in the land cover mix. Daytime Bowen ratios vary inversely with vegetation fraction between and within cities for all weather scenarios. Impervious surface cover is positively correlated to the available energy that is partitioned into sensible heat. Cumulative evapotranspiration (ET) is similar for average weather conditions across medium wet sites in Phoenix and Portland but varies more in Portland than in Phoenix under extreme weather conditions. Results suggest that land cover manipulation could offset influences of weather extremes on ET in Portland to a certain degree but not in Phoenix. These findings highlight the importance of spatial and climatic context in the urban design process to mitigate the effects of urbanization. Copyright © 2011 Royal Meteorological Society
... As noted by the author, a limitation of the study was that the LUMPS model used micrometeorological data from a single weather station and did not account for neighborhood level variations (Gober et al., 2010). The same limitation was noted by Middel et al. (2012) in their attempts to parameterize LUMPS for surface energy balance (SEB) studies in Phoenix, AZ (USA) and Portland, OR (USA). DiGiovanni et al. (2013) found that ET estimates from regional weather stations did not perform as well as estimates from onsite micrometeorological data in comparison to actual ET rates measured from a green roof in New York City, NY (USA). ...
... urban green spaces is being adopted in cities across the world as a means for climate change adaptation and mitigation, further understanding of evapotranspiration will be required for effective planning. Using the Local-scale Urban Meteorological Parameterization Scheme (LUMPS) to model ET, Middel et al. (2012) concluded that under different climates, land cover strategies will have variable impacts on surface energy balances (SEB). ...
... Predicted vs. observed RET, Rsin, T, RH and u 2 for GR-QBG. and needs to be considered in evaluating ET rates, particularly in urban water and energy modeling (Oke, 1973;Eching and Snyder, 2005;Middel et al., 2012). ...
Variability in micrometeorological conditions and their influence on estimated reference evapotranspiration (RET) rates were evaluated across a heterogeneous urban environment. Micrometeorological data sets (incoming solar radiation, air temperature, relative humidity and wind speed) were collected over a one-year period at six weather stations in New York City, NY (USA). Weather stations are located at four new urban green space monitoring sites and two airports. Reference evapotranspiration (RET) rates were estimated from the micrometeorological data sets for a short reference surface at a daily time-step using the ASCE Standardized Reference Evapotranspiration Equation, a Penman-Monteith based combination equation. Non-parametric comparative statistical analyses (Kruskal-Wallis) revealed statistically significant differences (at significance level α = 0.05) in micrometeorological conditions and estimated RET rates between the six sites. On a cumulative annual basis, estimated RET varied by up to 40 percent between the sites. A new technique for adjusting weather data collected at one location (e.g. regional airports) for use at another location (e.g. interior engineered urban green spaces) was evaluated. The study highlights the importance, for accurate estimation of ET, of onsite micrometeorological data sets, but concludes that additional research is needed to more thoroughly characterize micrometeorological variability across heterogeneous urban environments, and also to evaluate the influence of non-meteorological determinants, e.g. vegetation type, soil/media type, media moisture conditions and anthropogenic heat fluxes, on urban ET.
... Consequently, the effects of UHI vis-à-vis the changes in Land Cover over time is one of the major issues which needs to be addressed globally for achieving sustainable development. Further, mitigating heat island effects is all the more of paramount importance in urban areas, especially because UHI effects are locally of greater magnitude than projected global climate change effects and they increase the urban population's vulnerability to future global environmental change [11,12]. ...
... It has been well established through numerous field experiments and simulations that the urban texture significantly affects the urban microclimate [21]. Through urbanization, natural surfaces are replaced by materials with higher material heat capacity and thermal conductivity, different moisture characteristics, and different radiative properties (lower surface albedo and emissivity) which contribute to higher temperatures [11]. In order to validate the observations on LST differences and UHI effects over the city of Bhubaneswar, changes in land cover over this Impact of Rapid Urbanization on the City of Bhubaneswar, India 123 region has been analysed for a 15 year period coinciding with the primary analysis. ...
... These changes are sure indicators of urbanization and thus support the results of our earlier analysis on LST changes and UHI effects. Several earlier works have attributed anthropogenic alterations of surface morphology due to urbanization to significant changes in the local surface energy balance thus creating a new, local microclimate [11,[22][23][24][25][26][27]. Srivastava et al. [10] in their analysis of an Indian city like Mumbai have attributed UHI affects to the modification of the land surface by urban development, which uses materials that effectively retain heat and the emission of heat by human activities. ...
Rapid and unplanned urbanization of cities has been a cause of great concern world over. Increased urbanization has immensely altered the Land Use pattern of several Indian cities, thereby altering the physical properties of the land surface. The pronounced effect of urban heat island (UHI) apart from the acute stress on limited natural resources are consequences of this rapid urbanization. UHI effect manifests as unexpected rise in city temperatures when compared to their surrounding areas, thus making them unfriendly for habitation over time. The present work analyses the effect of UHI on Bhubaneswar, an Indian city undergoing rapid urbanization in recent times, utilizing land use and land cover (LULC) change data from Landsat over a 25 km radius about the city and MODIS land surface temperatures (LST) at 1 km² spatial resolution for a period of 15 years (2000–2014). From the study, significant changes in LULC through over-exploitation of natural resources and the related spatio-temporal variations in LST has been identified as one major factor responsible for changes in the UHI effect over Bhubaneswar. Owing to rapid urbanization (83% increase in 15 years), the city has undergone major changes in LULC aggregating to a massive ~ 89% decrease in dense vegetation and ~ 83% decrease in crop fields over this time period. Analyses of the changes in the urban energy balance and resulting UHI effect across many such Indian cities undergoing rapid urban growth is quite essential for mitigating the negative impacts of urbanization for a long-term sustainability.
... So, while an agency may be pursuing deployment of green roofs or rain gardens for storm water management, it may miss the implications of such technologies for urban heat, building energy, and air quality. Taking urban vegetation as an example, there is ample empirical and modeling evidence of the potential for urban vegetation to significantly reduce urban air temperatures (e.g., [11][12][13]), although water availability is a key determinant of performance [14]. Some important implementation issues, however, are often not considered. ...
... While an extensive amount of literature has examined the influence of land cover changes in cities on heat island formation [1,3,14], and the health impacts of high temperatures [31], few studies have explicitly sought to link UHI formation directly to human health outcomes. One of the first studies to address this question [33] used a global circulation model (GISS) coupled with a regional climate model (MM5) to assess the impact of globally-and regionally-driven warming on heat-related mortality in New York by 2050. ...
We use the Northeast US Urban Climate Archipelago as a case study to explore three key limitations of planning and policy initiatives to mitigate extreme urban heat. These limitations are: (1) a lack of understanding of spatial considerations-for example, how nearby urban areas interact, affecting, and being affected by, implementation of such policies; (2) an emphasis on air temperature reduction that neglects assessments of other important meteorological parameters, such as humidity, mixing heights, and urban wind fields; and (3) too narrow of a temporal focus-either time of day, season, or current vs. future climates. Additionally, the absence of a direct policy/planning linkage between heat mitigation goals and actual human health outcomes, in general, leads to solutions that only indirectly address the underlying problems. These issues are explored through several related atmospheric modeling case studies that reveal the complexities of designing effective urban heat mitigation strategies. We conclude with recommendations regarding how policy-makers can optimize the performance of their urban heat mitigation policies and programs. This optimization starts with a thorough understanding of the actual end-point goals of these policies, and concludes with the careful integration of scientific knowledge into the development of location-specific strategies that recognize and address the limitations discussed herein.
... So, while an agency may be pursuing deployment of green roofs or rain gardens for storm water management, it may miss the implications of such technologies for urban heat, building energy, and air quality. Taking urban vegetation as an example, there is ample empirical and modeling evidence of the potential for urban vegetation to significantly reduce urban air temperatures (e.g., [11][12][13]), although water availability is a key determinant of performance [14]. Some important implementation issues, however, are often not considered. ...
... While an extensive amount of literature has examined the influence of land cover changes in cities on heat island formation [1,3,14], and the health impacts of high temperatures [31], few studies have explicitly sought to link UHI formation directly to human health outcomes. One of the first studies to address this question [33] used a global circulation model (GISS) coupled with a regional climate model (MM5) to assess the impact of globally-and regionally-driven warming on heat-related mortality in New York by 2050. ...
... Results also showed that a more compact city with higher building density and fewer impervious surfaces improved nighttime cooling rates with marginal increases in outdoor water use. This line of inquiry was extended to the Portland area by Middel et al. (2011a), who investigated the sensitivity of LUMPS outputs to varying climate and land-surface conditions (model results are highly sensitive to solar radiation), and House-Peters and Chang (2011a) who considered the effects of climate change on the SEB in Portland suburb of Hillsboro. Findings from the latter study showed that a warming climate raises evapotranspiration (ET), prompting us to speculate that Portland would require sizeable additions of outdoor water to retain current landscapes and manage heat in a warmer climate. ...
... We viewed LUMPS as a vehicle to explore alternative urban futures rather than as a method to predict the future. Interactions between changes in land cover fractions are, in fact, the subject of more detailed analysis in Middel et al. (2011a). Second, ET is not strictly the equivalent of outdoor water use, especially in Portland. ...
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.
... Results show that customers in hot dry climates purchase more water than those in wetter and cooler ones (Coomes et al. 2010) and that residents in neighborhoods impacted by urban heat island effects use more water, all things being equal, than other urban residents Gober 2007, 2010). At the heart of these studies is an interest in urban sustainability, including tradeoffs between temperature amelioration (UHI mitigation) and urban water use (Middel et al. 2011). ...
... There have been, however, no systematic efforts to analyze the space/time dynamics of urban water use as they vary by both climatic and land cover characteristics. Recently, Middel et al. (2011) examined the effects of urban land development on temperature and the surface energy balance. We build on this previous work to examine the effects of biophysical land cover characteristics and local climate conditions on residential water use in Phoenix and Portland at fine geographic and temporal scales. ...
Critical to effective urban climate adaptation is a clearer understanding of the sensitivities of resource demand to changing climatic conditions and land cover situations. We used Bayesian Maximum Entropy (BME) stochastic procedures to estimate temperature and precipitation at the very small scale of urban Census Block Groups (CBGs) in Phoenix, Arizona and Portland, Oregon, and then compared average household water use patterns by climate conditions and land cover characteristics between and within the two cities. Summer household water use was positively related to maximum temperatures and dense vegetation cover in terms of grass cover and trees and shrubs; it was negatively related to precipitation amounts in both cities. Water use was more sensitive to maximum temperature, precipitation levels, and vegetation cover in Phoenix than in Portland. There was substantial intra-city variation with greater sensitivity in urban water use associated with higher densities of trees and shrubs in both cities, but in Phoenix, the highest sensitivities to maximum temperatures occurred in CBGs with the most grass cover while in Portland, high sensitivity was associated with CBGs with the least grass cover. Many of the latter are in highly built-up downtown areas of Portland where artificial irrigation is required to maintain landscapes during the hot summer season. Take-home messages are: (1) BME space/time statistics provide efficient estimates of missing precipitation and temperature data to create continuous high resolution meteorological data that improve water demand analysis and (2) use of landscaping for urban climate adaptation will have differing impacts on water use, depending on local climate conditions, urban layout, and the type of vegetation cover.
... One method of ameliorating daytime and nighttime temperatures is to increase the amount of vegetation, providing cooling through shading and evapotranspiration. In desert cities, where water resources are scarce, this approach creates a cooling-water use tradeoff that needs to be optimized to find a sustainable balance between temperature reduction achieved and the amount of water used Middel, Brazel, Gober, et al., 2012;Middel, Brazel, Kaplan, & Myint, 2012;Shashua-Bar, Pearlmutter, & Erell, 2009). However, the most sustainable solution may not be the best from a human vulnerability standpoint (Jenerette, Harlan, Stefanov, & Martin, 2011;Middel, Brazel, Kaplan, et al., 2012). ...
... The results of this study confirm prior efforts that found substantial air temperature cooling benefits from vegetation (Guhathakurta & Gober, 2010;Middel, Brazel, Gober, et al., 2012;Middel, Brazel, Kaplan, et al., 2012). Mesic sites were found to be the coolest landscapes, followed by oasis then xeric. ...
This study investigates the impact of urban form and landscaping type on the mid-afternoon microclimate in semi-arid Phoenix, Arizona. The goal is to find effective urban form and design strategies to ameliorate temperatures during the summer months. We simulated near-ground air temperatures for typical residential neighborhoods in Phoenix using the three-dimensional microclimate model ENVI-met. The model was validated using weather observations from the North Desert Village (NDV) landscape experiment, located on the Arizona State University's Polytechnic campus. The NDV is an ideal site to determine the model's input parameters, since it is a controlled environment recreating three prevailing residential landscape types in the Phoenix metropolitan area (mesic, oasis, and xeric). After validation, we designed five neighborhoods with different urban forms that represent a realistic cross-section of typical residential neighborhoods in Phoenix. The scenarios follow the Local Climate Zone (LCZ) classification scheme after Stewart and Oke. We then combined the neighborhoods with three landscape designs and, using ENVI-met, simulated microclimate conditions for these neighborhoods for a typical summer day. Results were analyzed in terms of mid-afternoon air temperature distribution and variation, ventilation, surface temperatures, and shading. Findings show that advection is important for the distribution of within-design temperatures and that spatial differences in cooling are strongly related to solar radiation and local shading patterns. In mid-afternoon, dense urban forms can create local cool islands. Our approach suggests that the LCZ concept is useful for planning and design purposes.
... To the authors' knowledge, no study to date has compared these local correlations across cities, although an increasing number of individual case studies on temperature, land use, and outdoor water use have emerged (Balling, Gober, & Jones, 2008;Hof & Schmitt, 2011;House-Peters, Pratt, & Chang, 2010). Previous comparative studies of water use in Portland and Phoenix have focused on feedback effects among water demand, irrigated vegetation, and the urban heat island effect (Gober, Middel et al., in press;Middel et al., 2011). Research findings suggest that a comparative geographic perspective on water use can highlight subtle but important trade-offs among urban form, vegetation distributions, and water demand patterns. ...
... Our research approach leverages these differences in land use and climate to draw out their effect on water use. We situate our work within a larger body of comparative research on the linkages among land cover, climate, and water use in Portland and Phoenix (Gober, Middel et al., in press;Middel et al., 2011). Results from this research have implications for cities where connections between land use and water use are often overlooked in planning and development. ...
... As shown in Fig. 12, about 20% of the solar radiation is absorbed by ozone, water, and the atmosphere, about 30% is scattered by air molecules, dust, and small water droplets, and the rest can reach the ground unhindered (Middel et al., 2012;Oke & Stewart, 2012). The solar radiation that reaches the ground consists of two parts: parallel rays that directly reach the ground, called direct solar radiation; additional, non-parallel rays that reach the ground from all directions in the sky after being scattered by the atmosphere, called scattered radiation (Castaldo et al., 2018). ...
The “Laochi” public space (LPS), which has existed for hundreds of years, has been gradually replaced by infrastructure during rural reconstruction. This study provides suggestions to protect the LPS with rural sustainable development by analyzing its effect on outdoor thermal environment. The Pearson correlation coefficient, root mean square error (RMSE), and mean absolute percentage error (MAPE) were used to verify the applicability of the ENVI-met model on typical villages in Northwest China. Additionally, the thermal effects of different underlying surfaces on rural environments were compared according to heat parameters through numerical simulation. The results showed mostly accurate predictions by the microclimate software. Furthermore, the LPS could effectively reduce the air temperature and increase the relative humidity of the settlement, especially during the daytime. Besides, compared with the current scenario (soil), concrete and brick paving increased the outdoor air temperature by 1.6% and 0.94%, respectively, while grassland and waterbody decreased air temperature by 0.75% and 1.23%, respectively. Based on these findings, some policy formulations and changes were recommended to local governments. Moreover, rural sustainable development showed great significance in the creation of a healthier ecological sustainable rural settlement.
... Most studies on UHI were focused on the summer (Kolokotroni and Giridharan, 2008;Middel et al., 2012;Zhang et al., 2017a;Lam and Lau, 2018;) because this UHI effect is significant during the hot season, the radiation of the solar energy makes the surface stored more heat during the daytime. Thus studies showed that surface urban heat island (SUHI) is related to the surface albedo and heat transfer by the coverage materials (Bhattacharya et al., 2009;Erell et al., 2014). ...
Most of the urban heat island (UHI) researches focused on the phenomenon in summer. They mainly studied the causes, different functional areas, and possible mitigation measures to reduce the high temperature in urban areas. However, UHI also exists in winter, but there are a limited number of studies on winter UHI. The characteristics and causes of UHI in winter have not been received much attention or consideration yet. This study aims to characterize the UHI feature in winter in Budapest, Hungary, based on the analysis of land surface temperature (LST) in relation to the factors of elevation, slope exposure, residential type, and snow coverage. Five different Landsat images in the winter season were applied to detect the surface temperature; besides, pictures of the thermal camera at a micro-scale were also used. Results showed that UHI intensity was not strong in winter; built-up areas were warmer than other urban areas. Topography was one of the significant factors affecting the surface temperature in winter. The surface temperature of the hills (300 m asl) was lower than that of the lowlands (below 120 m asl). The south-facing slopes and south oriented buildings were warmer than north-facing slopes and buildings oriented to the north. Areas with snow coverage had a lower temperature than no snow coverage areas. These findings could give general guidance for further UHI research, urban planning as well as landscape design.
... 4,5 The anthropogenic alterations of surface morphology due to urbanization (increase in urban infrastructure) result in signicant changes in the local surface energy balance. [6][7][8][9] These have a direct effect on land surface temperature (LST) and heat uxes giving rise to the urban heat island (UHI) effect apart from contributing to global warming. 10,11 Increases in LST in the urban agglomerates are further exacerbated by modication of the land surface that uses materials that effectively retain heat due to different bulk thermal properties in addition to continued emission of heat by human activities. ...
The COVID-19 pandemic forced a nationwide lockdown in India for months when close to 1.3 billion people were confined to their homes. An abrupt halt in the majority of the urban activities reduced the generation of anthropogenic heat which often exacerbates the Urban Heat Island (UHI) effect in the urban pockets of the country. We studied the lockdown impact on seven highly populated and polluted mega urban agglomerations across India, namely Delhi, Ahmedabad, Hyderabad, Kolkata, Mumbai, Bengaluru and Chennai using near-anniversary Landsat 8 data. The results revealed that the lockdowns have improved the air quality and reduced the Land Surface Temperature (LST) and hence the UHI effect over those cities. Each of the cities experienced an improved Air Quality Index (AQI) ranging from 18 to 151 units except Chennai with a marginal AQI increase by 8 units, a decrease in mean LST in the range of 0.27 ⁰C to 7.06 ⁰C except Kolkata which showed an increment by ~4 ⁰C, and a reduction in daily averaged air temperature ranging from 0.3 ⁰C to 10.88 ⁰C except Hyderabad with an increase of 0.09 ⁰C during the lockdown (April 2020) compared to the previous years (April 2019 and 2018). Delhi exhibited the maximum positive impact of the lockdown in all aspects with two-fold improved air quality, and Ahmedabad showed the least improvement. In addition to the variations in regional land use and land cover and proportion of essential industries that remained operational throughout the lockdown, the geographic location, topography, local meteorology and climate were some of the other factors also responsible for either aiding or overcompensating the large scale LST variabilities observed in these cities. These results hint at an unprecedented opportunity to evaluate the effectiveness of periodic planned lockdowns as a possible mitigating measure to reduce LST spikes and degraded air quality in urban areas in the future.
... Enhancing services entails increasing the multifunctionality of landscapes, which necessitates managing social-ecological interactions that can result in tradeoffs and synergistic outcomes (Fagerholm et al., 2019). One example of tradeoffs in urban landscapes is between water conservation and heat mitigation, since vegetation often requires irrigation but provides cooling benefits (Middel et al., 2012). Another interchange is between biodiversity outcomes and aesthetic benefits, since the vegetation structure that provides wildlife habitat can often be perceived as messy and disorderly (Nassauer, 1995). ...
Local regulations on residential landscapes (yards and gardens) can facilitate or constrain ecosystem services and disservices in cities. To our knowledge, no studies have undertaken a comprehensive look at how municipalities regulate residential landscapes to achieve particular goals and to control management practices. Across six U.S. cities, we analyzed 156 municipal ordinances to examine regional patterns in local landscape regulations and their implications for sustainability. Specifically, we conducted content analysis to capture regulations aimed at: 1) goals pertaining to conservation and environmental management, aesthetics and nuisance avoidance, and health and wellbeing, and 2) management actions including vegetation maintenance, water and waste management , food production, and chemical inputs. Our results reveal significant variation in local and regional regulations. While regulatory goals stress stormwater management and nuisance avoidance, relatively few municipalities explicitly regulate residential yards to maintain property values, mitigate heat, or avoid allergens. Meanwhile, biological conservation and water quality protection are common goals, yet regulations on yard management practices (e.g., non-native plants or chemical inputs) sometimes contradict these purposes. In addition, regulations emphasizing aesthetics and the maintenance of vegetation, mowing of grass and weeds, as well as the removal of dead wood, may inhibit wildlife-friendly yards. As a whole, landscaping ordinances largely ignore tradeoffs between interacting goals and outcomes, thereby limiting their potential to support landscape sustainability. Recommendations therefore include coordinated, multiobjective planning through partnerships among planners, developers, researchers, and non-government entities at multiple scales.
... In addition, trees have esthetic benefits and other vegetation helps to alleviate the effects of the urban heat island by reducing the heat flow leading to increased heat flow through evapotranspiration and low air temperatures (Anyanwu and Kanu 2006;Tan et al. 2016). In terms of air temperature studies, cool places are closely linked to much vegetation (Lindén 2011;Middel et al. 2012;Alavipanah et al. 2015;Fan et al. 2015;Norton et al. 2015). Harlan et al. (2006) show that increased urban vegetation is strongly associated with improved thermal comfort conditions, especially during heatwaves. ...
Urbanization models that do not comply with the planning criteria are affecting human lives. In urban areas, street trees have positive contributions to the ecosystem and human thermal comfort. In this study, the thermal comfort of the main streets that connect people to each other and provide access and transportation has been thermally explored. Cumhuriyet Street, which is one of the vibrant streets in Erzurum, was selected as a case study scenario in the winter and summer periods in 2018 by using the ENVI-met V. 4.4.2 winter model. A different green scenario is proposed, and the best thermal comfort scenario in both seasons is determined. The results show that, in the summer period, the air temperature of the greener street scenario is about 1.0°C cooler than the existing condition and about 2.0°C warmer in the winter period. Physiological equivalent temperature (PET) value was better in narrow canyon streets in winter months, but in wide canyon streets in summer months. The green scenarios of wide canyon streets positively affect the outdoor thermal comfort in both seasons. These results clearly imply that green streets are an appropriate strategy for city streets that suffer from discomfort levels in cold winter and hot summer periods. It has been concluded that it is possible to increase thermal comfort through improvement in the open space in street and more suitable plant preferences for livable urbanization. Planning streets in a new city characterized by summer and winter seasons should take into consideration an accurate decision for providing a thermal comfort level and healthy urbanization.
... Accurate replication of plants, especially trees, has been handled rather crudely. However, there is general consensus about the importance of urban vegetation with regard to mitigating the urban heat island [1][2][3][4][5][6]. The key positive effects of urban vegetation onto thermal comfort are lowering air and radiative temperature via evaporative cooling and shading [6][7][8]. ...
While complex urban morphologies including different materials, wall structures, etc., are rather adequately represented in microclimate models, replication of actual plant geometry is-so far-rather crudely handled. However, plant geometry greatly differs within species and locations while strongly determining a plant's microclimate performance. To improve the plants representation in numerical models, a new method to describe plant skeletons using the so-called Lindenmayer-System has been implemented in the microclimate model ENVI-met. The new model allows describing much more realistic plants including the position and alignment of leaf clusters, a hierarchical description of the branching system and the calculation of the plant's biomechanics. Additionally, a new canopy radiation transfer module is introduced that allows not only the simulation of diffuse radiation extinction but also secondary sources of diffuse radiation due to scattering of direct radiation within plant canopies. Intercomparisons between model runs with and without the advancements showed large differences for various plant parameters due to the introduction of the Lindenmayer-System and the advanced radiation scheme. The combination of the two developments represents a sophisticated approach to accurately digitize plants, model radiative transfer in crown canopies, and thus achieve more realistic microclimate results.
... Land cover is one of the key factors affecting the energy balance of surface solar radiation [1][2][3][4]. Changes in land cover and its spatial distribution have important impacts on global environmental change, climate change, the energy cycle of earth ecosystems, regional resources, and the sustainable development of economy and society [5][6][7][8]. At present, surface land-cover information and dynamic changes form the basis of scientific research in many fields, such as environmental modeling and soil erosion [9,10]. ...
Analyzing consistency of different land-cover data is significant to reasonably select land-cover data for regional development and resource survey. Existing consistency analysis of different datasets mainly focused on the phenomena of spatial consistency regional distribution or accuracy comparison to provide guidelines for choosing the land-cover data. However, few studies focused on the hidden inconsistency distribution rules of different datasets, which can provide guidelines not only for users to properly choose them but also for producers to improve their mapping strategies. Here, we zoned the Sindh province of Pakistan by the Terrestrial Ecoregions of the World as a case to analyze the inconsistency patterns of the following three datasets: GlobeLand30, FROM-GLC, and regional land cover (RLC). We found that the inconsistency of the three datasets was relatively low in areas having a dominant type and also showing homogeneity characteristics in remote sensing images. For example, cropland of the three datasets in the ecological zoning of Northwestern thorn scrub forests showed high consistency. In contrast, the inconsistency was high in areas with strong heterogeneity. For example, in the southeast of the Thar desert ecological zone where cropland, grassland, shrubland, and bareland were interleaved and the surface cover complexity was relatively high, the inconsistency of the three datasets was relatively high. We also found that definitions of some types in different classification systems are different, which also increased the inconsistency. For example, the definitions of grassland and bareland in GlobeLand30 and RLC were different, which seriously affects the consistency of these datasets. Hence, producers can use the existing land-cover products as reference in ecological zones with dominant types and strong homogeneity. It is necessary to pay more attention on ecological zoning with complex land types and strong heterogeneity. An effective way is standardizing the definitions of complex land types, such as forest, shrubland, and grassland in these areas.
... These may cause changes in the heat fluxes between the surface and the atmosphere, which affect the energy balance. Therefore, the heat transport, vapor formation, precipitation, and wind field will be affected, as well as the dispersion of pollutants (Pielke et al. 2002;Brazel et al. 2007;Martilli 2007;Middel et al. 2012;Ge et al. 2014;Cao et al. 2015;Zhou et al. 2015;Kumar et al. 2016). Thus, establishing the relationship between land use changes and modeling prediction is important to obtain results closer to those measured in by loco monitoring networks (Levy et al. 2004;Freitas et al. 2005;Chiquetto and Silva 2010;Qu et al. 2013;Pereira et al. 2016). ...
This study evaluates the effect of the land use update to meteorological simulations in the Metropolitan Region of Greater Vitoria (MRGV) using the Weather Research and Forecasting (WRF) mesoscale model. WRF performance was analyzed using monitoring data like wind speed and direction, temperature, and sensible heat flux. In general, the changes in the simulations results with the updating of the land use data are quite subtle, and these values are better represented by the local data in the cold front period. The results obtained indicate a slight improvement in the wind speed and direction when land use is local for the airport station, where the mean bias reduced from − 0.124 to − 0.079, thereby better capturing smaller urban centers and the urban canopy.
... The research revealed large variations in LST changes in response to irrigation across different regions, with a cooling effect as much as 10°C. No matter what approach was applied, the mechanism in these bio-geophysical processes was elaborated by the perspective of energy budget balance (Grachev et al., 2017;Middel et al., 2012). ...
... As for Surface energy fluxes, the non-linear relationship between latent heat fluxes proportion (e.g., Bowen ratio) and the vegetative fraction was discovered in numerical simulations [27,28]. With a 3D geometry physical model, a linear pattern was detected between evaporation heat loss and the vegetative cover [29]. ...
... The effects of land-use heterogeneities on local climate and on the variability of vapour and energy fluxes have been studied using the atmospheric models (Pielke et al. 2002;Schneider et al. 2004;Douglas et al. 2006;Narisma and Pitman 2006). Several earlier works have been attributed anthropogenic alterations of the surface morphology due to change in LULC to significant changes in the local surface energy balance, thus creating a new, local microclimate (Bonan 2000;Pearlmutter et al. 2009;Middel et al. 2012;Pathirana et al. 2014). Since LULC changes have immediate and profound effect on the local weather and climate, and difficult to understand from global perspective (Pielke et al. 2011;Pitman et al. 2012), it is very important to understand and quantify the impacts of LULC changes on the local climate and weather through carefully designed sensitivity experiments with high-resolution Limited Area Model (LAM). ...
This study is about the impact assessment of different land-use data sets on the simulation of an Extreme Rainfall Event (ERE) which is one of the unusually rare events that occurred between 14th to 18th of June 2013 over Uttarakhand in India. In this work, high-resolution (2-km), time ensemble simulations are carried out using Weather Research and Forecasting model (WRFV3.5) with a 3-nest configuration. The sensitivity analysis of the model in simulating rainfall to different land-use data i.e. USGS-24 category (1992–93), ISRO (2004–05) and (2012–13) are carried out. Comparison of simulated rainfall which is averaged over the study region with that of IMD observed station data (averaged over 23 stations) showed that the simulations based on ISRO land-use data are comparatively more accurate with lesser simulation error when compared to simulations with USGS land-use data. The percentage of error in rainfall for the 3 simulations was found to be 24% (USGS), 9.5% (ISRO-2005) and 10% (ISRO-2013) with respect to the IMD observation. During the initial stage, the results have shown maximum convergence and vorticity with a strong updraft. The strong updraft, however, persisted throughout the simulation period. The increasing tendency of positive vorticity both in the simulation and observation suggests an intensification of cyclonic circulation in a vertical direction and hence creates instability in the boundary layer causing ERE over Uttarakhand. This study shows that ISRO land-use data is a relatively more realistic representation of the study region than the USGS data, and found to be useful in reducing the model error in the simulation of such rare events over this kind of mountainous region.
... Yet as Oke et al. (1998) demonstrated, this may not be the case. So while there has been an increase in studies of urban microclimate in tropical and wet subtropical areas (see review in Roth, 2007) the only desert city where microclimate has been studied extensively is Phoenix, Arizona (e.g., Baker et al., 2002;Brazel and Hedquist, 2006;Guhathakurta and Gober, 2010;Svoma and Brazel, 2010;Middel et al., 2012Middel et al., , 2014. This is despite the fact that several studies have found important differences between desert cities and temperate ones (Brazel et al., 2000;Lazzarini et al., 2015). ...
Mapping spatial and temporal variability of urban microclimate is pivotal for an accurate estimation of the ever‐increasing exposure of urbanized humanity to global warming. This particularly concerns cities in arid/semi‐arid regions which cover two fifths of the global land area and are home to more than one third of the world's population. Focusing on the desert city of Be'er Sheva Israel, we investigate the spatial and temporal patterns of urban‐rural and intra‐urban temperature variability by means of satellite observation, vehicular traverse measurement, and computer simulation. Our study reveals a well‐developed nocturnal canopy layer urban heat island in Be'er Sheva, particularly in the winter, but a weak diurnal cool island in the mid‐morning. Near surface air temperature exhibits weak urban‐rural and intra‐urban differences during the daytime (< 1oC), despite pronounced urban surface cool islands observed in satellite images. This phenomenon, also recorded in some other desert cities, is explained by the rapid increase in surface skin temperature of exposed desert soils (in the absence of vegetation or moisture) after sunrise, while urban surfaces are heated more slowly. The study highlights differences among the three methods used for describing urban temperature variability, each of which may have different applications in fields such as urban planning, climate change mitigation and epidemiological research. This article is protected by copyright. All rights reserved.
... The previous researches that focused on the urban energy modeling have stated on energy related carbon emission (Yi, et al., 2013), energy potential mapping (Broersma, Fremouw and Dobbelsteen, 2013) and the urban energy balancing model (Middel, et al., 2011;Balogun et al., 2009;Grimmond et al., 2010;Christen and Vogt, 2004;Coutts et al., 2007;Kalanda et al., 1980;Piringer et al., 2007;Mitchell et al., 2008). This research focuses on urban energy modelling. ...
... Vegetation plays a vital role in urban environments: Aside from the aesthetic benefits, trees and other vegetation help mitigate the effects of the urban heat island by increasing the latent heat flux through evapotranspiration and decreasing the sensible heat flux through shading, resulting in lower air temperatures (Anyanwu & Kanu, 2006;Yu & Hien, 2006). Studies of the ambient air temperature in cities have shown a mosaic of cooler and warmer places, with cooler places being closely connected to increased vegetation cover (Alavipanah, Wegmann, Qureshi, Weng, & Koellner, 2015;Fan, Myint, & Zheng, 2015;Harlan, Brazel, Prashad, Stefanov, & Larsen, 2006;Lindén, 2011;Middel et al., 2012;Norton et al., 2015). Harlan et al. (2006) demonstrate that increased urban vegetation strongly correlates with improved thermal comfort conditions, particularly during heat waves. ...
Increasing vegetation cover in cities is a key approach to mitigating urban heat excess. However, both the effect of vegetation on microclimate and the plants' vitality need to be assessed to support and quantify the effects of such strategies. One way to assess the interactions between vegetation and the urban environment is through microclimate models that can simulate the effects of vegetation onto the urban microclimate as well as effects of urban environments onto vegetation. To provide reliable estimates microclimate models need to be para-meterized based on empirically obtained data. In this paper we compare modeled transpiration rates and leaf temperatures of a leading microclimate model, ENVI-met V4, with in-situ measured stem sap flow and leaf temperatures of two different trees in an urban courtyard. The vegetation model of ENVI-met is evaluated considering four synoptic situations including varying cloud covers ranging from fully cloudy to clear sky. The comparison of simulation results with empirical data reveals a high agreement. The model is capable of capturing the magnitude as well as short-term variations in transpiration caused by microclimatic changes. However, substantial deviations were found in situations with low photosynthetic active radiation. Modeled and observed diurnal tree transpiration and leaf temperature showed good agreement. These findings indicate that ENVI-met is capable of simulating transpiration rates and leaf temperatures of trees in complex urban environments .
... Understanding the links between urban land cover and the SEB processes that influence microclimatic conditions is critical for planning and design purposes Middel et al., 2012;Mitchell et al., 2008;Wang et al., 2016), in particular, for cities facing an urban heat island. In the Phoenix, Arizona, metropolitan area, rapid urbanization during the second half of the twentieth century led to the conversion of agriculture and desert lands into urban and suburban developments (e.g., Hirt et al., 2008;Jenerette et al., 2011). ...
The impact of urbanization on water and energy fluxes varies according to the characteristics of the urban patch type. Nevertheless, urban flux observations are limited, particularly in arid climates, given the wide variety of land cover present in cities. To help address this need, a mobile eddy covariance (EC) tower was deployed at three locations in Phoenix, Arizona, to sample the surface energy balance (SEB) at a parking lot, a xeric landscaping (irrigated trees with gravel) and a mesic landscaping (irrigated turf grass). These deployments were compared to a stationary EC tower in a suburban neighborhood. A comparison of the observations revealed key differences between the mobile and reference sites tied to the urban land cover within the measurement footprints. For instance, the net radiation varied substantially among the sites in manners consistent with albedo and shallow soil temperature differences. The partitioning of available energy between sensible and latent heat fluxes was modulated strongly by the presence of outdoor water use, with the irrigated turf grass exhibiting the highest evaporative fraction. At this site, we identified a lack of sensitivity of turbulent flux partitioning to precipitation events which suggests that frequent outdoor water use removes water limitations in an arid climate, thus leading to mesic conditions. Other urban land covers with less irrigation, however, exhibited sensitivity to the occurrence of precipitation, as expected for an arid climate. As a result, quantifying the frequency and magnitude of outdoor water use is critical for understanding evapotranspiration losses in arid urban areas.
... Wind speed (m/s)이 증가하는 등의 요인으로 인해, 연 평균 기온이 0.5~1.0℃ 이상 상승하였다(Yun, 2002;O'Hare et al., 2005;Chung et al., 2004;Seto and Shepherd, 2009;Hu and Jia, 2010;Middel et al., 2010;Ahn et al., 2010;Cui and Shi, 2012; Janković and Hebbert, 2012;Kim and Yeom, 2012;Misra et al., 2012;Park and Tak, 2013;Li et al., 2013;Robaa, 2013).Relocation type Temperature ...
... (Lee, 1995;Barry and Chorley, 2003;O'Hare et al., 2005;Ahrens, 2006;Aguado and Burt, 2006;Lee, 2007;Hung, 2009;Kim et al., 2010) (Yun, 2002;Chung et al., 2004;O'Hare et al, 2005;Ahn et al., 2010;Hu and Jia, 2010;Middel et al., 2012;Misra et al., 2012;Li et al., 2013). ...
... While increasing impervious surface areas could reduce summer water use as evidenced by other studies (House-Peters and Chang, 2011b;Gober et al., 2012;Middel et al., 2012;Lee et al., 2015), higher impervious areas could also exacerbate existing urban heat island effects and reduce other ecosystem services in arid cities (e.g., in Phoenix, see references Jenerette et al., 2011;Wentz et al., 2016) and induce higher peak runoff and frequent localized flooding in the wet season (e.g., in Portland, see references Chang, 2007, Chang et al., 2010b. To minimize potential negative consequences of increasing impervious surface areas on urban water and ecosystem services, planners and decision-makers need to consider best management practices such as stormwater planning, porous pavement, green infrastructure (Pennino et al., 2016). ...
A growing body of literature examines urban water sustainability with increasing evidence that locally-based physical and social spatial interactions contribute to water use. These studies however are based on single-city analysis and often fail to consider whether these interactions occur more generally. We examine a multi-city comparison using a common set of spatially-explicit water, socioeconomic, and biophysical data. We investigate the relative importance of variables for explaining the variations of single family residential (SFR) water uses at Census Block Group (CBG) and Census Tract (CT) scales in four representative western US cities – Austin, Phoenix, Portland, and Salt Lake City, - which cover a wide range of climate and development density. We used both ordinary least squares regression and spatial error regression models to identify the influence of spatial dependence on water use patterns. Our results show that older downtown areas show lower water use than newer suburban areas in all four cities. Tax assessed value and building age are the main determinants of SFR water use across the four cities regardless of the scale. Impervious surface area becomes an important variable for summer water use in all cities, and it is important in all seasons for arid environments such as Phoenix. CT level analysis shows better model predictability than CBG analysis. In all cities, seasons, and spatial scales, spatial error regression models better explain the variations of SFR water use. Such a spatially-varying relationship of urban water consumption provides additional evidence for the need to integrate urban land use planning and municipal water planning.
... Although numerous studies of urban climate have shown that cooler places within the city are closely connected to an increased vegetation cover (Alavipanah et al., 2015;Fan et al., 2015;Harlan et al., 2006;Lindén, 2011;Middel et al., 2012;Norton et al., 2015), the diurnal variations as well as influence of changing weather conditions on the transpiration-induced cooling are still unclear. For example, cooling was strongest in the afternoon in irrigated parks and parks in humid climates (Jonsson, 2004;Potchter et al., 2006;Spronken-Smith and Oke, 1998). ...
... Table 2 and Fig. 2 provide an overview of the four sites included in this work. SUEWS has mostly been applied in temperate climates though the simpler model LUMPS has been applied in arid environments before (Middel et al., 2012). Here we applied SUEWS to a newly (< 2 years) instrumented site in Dublin, Ireland; a long term (5-10 years) site in Hamburg; Germany; a long term site in Melbourne, Australia; and an established site (2-4 years) in Phoenix, USA. ...
... Building upon the literature, we detail how our place-based research has advanced knowledge as well as strategies for dealing with complexity and uncertainty through adaptive approaches. While most DCDC research has been centered on the desert study region of metropolitan Phoenix, some studies-leveraged with additional resources from other grants and projects-have been comparative in nature [40,44]. For example, we focus in particular in this analysis on how a National Oceanographic and Atmospheric Administration (NOAA) sponsored study of arid Phoenix, Arizona and humid Portland, Oregon has expanded knowledge through comparative analysis of land-water-climate dynamics and how they play out across these rather different biomes. ...
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.
... In Miami's residential areas, decreased tree and vegetation cover (Nowak and Greenfield 2012) and impervious surfaces that route rainfall away from homes appeared to warm and dry the microclimate compared with dense, native subtropical forest and moist soils that retain rainfall. These patterns support the findings of other cross-city and modeling studies that show that daytime patterns of evapotranspiration and cooling are driven by the configuration and fraction of land covered by vegetation (Dimoudi and Nikolopoulou 2003;Middel et al. 2012). Additionally, the microclimate patterns shown here may be influenced by the apparent continental-scale convergence of hydrological features in US cities, which results in more surface water in dry cities and less surface water in wet cities compared with native ecosystems . ...
Context. The urban heat island (UHI) is a well- documented pattern of warming in cities relative to rural areas. Most UHI research utilizes remote sensing methods at large scales, or climate sensors in single cities surrounded by standardized land cover. Relatively few studies have explored continental-scale climatic patterns within common urban microenvironments such as residential landscapes that may affect human comfort.
Objectives. We tested the urban homogenization hypothesis which states that structure and function in cities exhibit ecological ‘‘sameness’’ across diverse regions relative to the native ecosystems they replaced.
Methods. We deployed portable micrometeorological sensors to compare air temperature and humidity in residential yards and native landscapes across six U.S. cities that span a range of climates (Phoenix, AZ; Los Angeles, CA; Minneapolis-St. Paul, MN; Boston, MA; Baltimore, MD; and Miami, FL).
Results. Microclimate in residential ecosystems was more similar among cities than among native ecosystems, particularly during the calm morning hours. Maximum regional actual evapotranspiration (AET) was related to the morning residential microclimate effect. Residential yards in cities with maximum AET 50–65 cm/year (Phoenix and Los Angeles) were generally cooler and more humid than nearby native shrublands during summer mornings, while yards in cities above this threshold were generally warmer (Baltimore and Miami) and drier (Miami) than native forests. On average, temperature and absolute humidity were ~6 % less variable among residential ecosystems than among native ecosystems from diverse regions.
Conclusions. These data suggest that common residential land cover and structural characteristics lead to microclimatic convergence across diverse regions at the continental scale.
... Numerous studies have considered the characteristics of urban vegetation in relation to its positive role in mitigating urban warming (Kaufmann et al., 2003; Sandholt et al., 2002; Van de Griend and Owe, 1993), including a large body of work on UHI mitigation through urban forestry in Phoenix (Buyantuyev and Wu, 2010; Jenerette et al., 2007; Myint et al., 2010). One study examined the urban surface energy balance in response to land-cover variations using a Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) (Middel et al., 2012). The investigation determined that urban vegetation can potentially reduce storage heat flux density and therefore plays an important role in UHI mitigation. ...
Urban forestry is an important component of the urban ecosystem that can effectively ameliorate temperatures by providing shade and through evapotranspiration. While it is well known that vegetation abundance is negatively correlated to land surface temperature, the impacts of the spatial arrangement (e.g. clustered or dispersed) of vegetation cover on the urban thermal environment requires further investigation. In this study, we coupled remote sensing techniques with spatial statistics to quantify the configuration of vegetation cover and its variable influences on seasonal surface temperatures in central Phoenix. The objectives of this study are to: (1) determine spatial arrangement of green vegetation cover using continuous spatial autocorrelation indices combined with high-resolution remotely-sensed data; (2) examine the role of grass and trees, especially their spatial patterns on seasonal and diurnal land surface temperatures by controlling the effects of vegetation abundance; (3) investigate the sensitivity of the vegetation-temperature relationship at varying geographical scales. The spatial pattern of urban vegetation was measured using a local spatial autocorrelation index—the local Moran’s Iv. Results show that clustered or less fragmented patterns of green vegetation lower surface temperature more effectively than dispersed patterns. The relationships between the local Moran’s Iv and surface temperature are evidenced to be strongest during summer daytime and lowest during winter nighttime. Results of multiple regression analyses demonstrate significant impacts of spatial arrangement of vegetation on seasonal surface temperatures. Our analyses of vegetation spatial patterns at varying geographical scales suggest that an area extent of ˜200 m is optimal for examining the vegetation-temperature relationship. We provide a methodological framework to quantify the spatial pattern of urban features and to examine their impacts on the biophysical characteristics of the urban environment. The insights gained from our study results have significant implications for sustainable urban development and resource management.
... Surface energy balance (SEB), which is partitioning of net available radiation energy into dissipative turbulent fluxes of sensible, latent and soil heat at a particular site depends upon the surface morphology (Middel et al., 2012). It also depends on the land surface temperature and the soil moisture content at any site (Bateni and Entekhabi, 2012). ...
Turbulent surface energy exchanges from land-air interface play an important role in generation and enhancing the convection. During pre-monsoon months (April to May) thunderstorms generate over Chota Nagpur plateau area of NE India and moves over the study area Ranchi (23°25′ N, 85°26′ E). Even though convective conditions prevail over Ranchi during these months, thunderstorm occurs on some days only. To address this important aspect, present study focuses on understanding of surface energy budget (SEB): partitioning of net solar radiation flux (QN) in to sensible (QH), latent heat (QE) and soil heat fluxes during different epochs of thunderstorm activity over study site at Ranchi. For this purpose, micro-meteorological data sets which comprises of fast response turbulent measurements and slow response data during 2008, 2009 and 2010 over Ranchi are used. A total 25 thunderstorm cases are selected for the present study. The study reveals that prior to the occurrence of thunderstorm the QH and QE fluxes reaches the same order followed by soil heat flux (QG). No significant variation of soil heat (QG) flux is noticed between thunderstorm days and non-thunderstorm days. The variations in the partitioning of QN flux in to QH, QE and QG fluxes are distinguishable between the days of thunderstorm (TD) and non thunderstorm (NTD). This variation can be used as precursor signal for the occurrence of thunderstorm activity. The results emanated form the present work is important in validating the performance of the meso-scale models in simulating these storms.
... It has an arid climate with extremely hot summers and mild winters. July is the warmest month of the year with a mean maximum temperature of 41.4°C, and a mean minimum exceeding 27°C [Middel et al., 2012]. During the previous decade the population grew by 29% to 4.1 million people [U.S. Census Bureau, 2010] making it one of the largest metropolitan areas in the United States. ...
This article investigates the effect of air-conditioning (AC) systems on air temperature and examines their electricity consumption for a semiarid urban environment. We simulate a 10-day extreme heat period over the Phoenix metropolitan area (US) with the Weather Research and Forecasting (WRF) model coupled to a multilayer building energy scheme. The performance of the modeling system is evaluated against ten Arizona Meteorological Network (AZMET) weather stations and one weather station maintained by the National Weather Service (NWS) for air temperature, wind speed, and wind direction. We show that explicit representation of waste heat from air-conditioning systems improved the 2 m-air temperature correspondence to observations. Waste heat release from AC systems was maximum during the day but the mean effect was negligible near the surface. However, during the night, heat emitted from AC systems increased the mean 2 m-air temperature by more than 1 °C for some urban locations. The AC systems modified the thermal stratification of the urban boundary layer promoting vertical mixing during nighttime hours. The anthropogenic processes examined here (i.e., explicit representation of urban energy consumption processes due to AC systems) require incorporation in future meteorological and climate investigations to improve weather and climate predictability. Our results demonstrate that releasing waste heat into the ambient environment exacerbates the nocturnal urban heat island and increases cooling demands.
... While there has been ample research into Phoenix's urban climate, in particular the UHI phenomenon within the boundaries of its metropolitan area (Fernando et al., 2010;Jenerette et al., 2011;Lee et al., 2012), much less focus has ensued on the fundamental surface energetics and its influence on near-surface climate. Several recent papers have modelled seasonal variations of urban SEB with LUMPS in Phoenix (Middel et al., 2012a(Middel et al., , 2012b, but there is an absence of long-term in situ observational platforms in the city. ...
Observations of local-scale urban surface energy balance (SEB), which include fluxes of net all-wave radiation (Q*), and eddy covariance measurements of sensible (QH) and latent heat (QE) were collected in an arid Phoenix, AZ suburb from January to December 2012. We studied diurnal variations in SEB partitioning over four distinct seasons: winter, equinoxes, and summer; the latter period is further subdivided into (1) months prior to and (2) months occurring during the North American Monsoon. Largest flux densities were observed in summer, with most available energy partitioned into QH. Much less energy is partitioned into QE, but this term is strongly affected by monsoonal precipitation, where greater-than-average QE can be discerned for several days after storm events. The presence of a positive daily flux residual (RES) [i.e. Q* − (QH + QE)] for most of the summer indicates that anthropogenic heat (QF) from residential cooling is likely a significant factor influencing SEB. Analysis of hourly ensemble SEB fluxes during all seasons also indicates that RES is largest in the morning, but QH dominates in the afternoon. Results of SEB trends and magnitudes from Phoenix were also compared with other urban sites, especially in (sub)tropical cities. When normalized with net radiation terms, a consistent diurnal hysteresis between ensemble QH and RES occurs, suggesting a robust parameterization of this relationship for model development during clear-sky conditions. SEB dynamics also appear to be affected by local surface characteristics, with regular nocturnal negative QH associated with a high urban sky-view factor. Measured QE fluxes during dry seasons were larger than expected based on the small proportion of irrigated plan area vegetated surfaces. A probable explanation could be an enhanced micro-scale advective forcing of evapotranspiration arising from leading-edge effects over patchy residential lawns, which has possible implications for modelling evapotranspiration in hot arid cities.
... Surface energy balance (SEB), which is partitioning of net available radiation energy into dissipative turbulent fluxes of sensible, latent and soil heat at a particular site depends upon the surface morphology (Middel et al., 2012). It also depends on the land surface temperature and the soil moisture content at any site (Bateni and Entekhabi, 2012). ...
... This research employs a surface energy budget model, the Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) version 5 (Grimmond & Oke, 2002;Loridian et al., 2011), to calculate hourly scale sensible, latent, and storage fluxes during the month of August under multiple plausible future scenarios of urban development and air temperature change. Surface energy balance models have been used worldwide (for an extensive review see Grimmond et al. (2010), but most previous research projects have focused primarily on urban-rural comparisons (Christen & Vogt, 2004;Cleugh & Oke, 1986;Xu et al., 2008), comparisons across cities (Grimmond & Oke, 2002), or changes in one location under multiple scenarios Middel et al., 2011;Mitchell et al., 2008). Using surface energy models to evaluate alternative futures is a relatively new feature of UHI research Mitchell et al., 2008) and to the authors' knowledge, future temperature change scenarios derived from down-scaled Global Climate Models (GCMs) have not been used as model input. ...
... Given the substantial influence of land cover change on the surface energy balance and thus on climate, particularly local climate, greater care should be taken in representing land cover and changes to land cover within climate modeling scenarios (Comarazamy et al., 2010;Herb et al., 2008;Middel et al., 2012;Stohlgren et al., 1998). With this work we provide a straightforward method for evaluating land cover change and connecting such changes with population change anywhere in the United States. ...
Land cover changes affect local surface energy balances by changing the amount of solar energy reflected, the magnitude and duration over which absorbed energy is released as heat, and the amount of energy that is diverted to non-heating fluxes through evaporation. However, such local influences often are only crudely included in climate modeling exercises, if at all. A better understanding of local land conversion dynamics can serve to inform inputs for climate models and increase the role for land use planning in climate management policy. Here we present a new approach for projecting and incorporating metropolitan land cover change into mesoscale climate and other environmental assessment models. Our results demonstrate the relative contributions of different land development patterns to land cover change and conversion and suggest that regional growth management strategies serving to increase settlement densities over time can have a significant influence on the rate of deforestation per unit of population growth. Employing the approach presented herein, the impacts of land conversion on climate change and on parallel environmental systems and services, such as ground water recharge, habitat provision, and food production, may all be investigated more closely and managed through land use planning.
Outdoor use in cities has increased considerably with the COVID-19 outbreak. Outdoor use is related to whether the spaces are comfortable or not. The more comfortable the outdoor spaces are in terms of thermals, the more intensive its use. Erzurum city is a winter city and is located in Dsb climate class. It has a very hot and dry climate in summer due to its high altitude, and a very harsh and cold climate in winter. Havuzbaşi City Square, which is one of the most used squares in Erzurum city center, was chosen as the working area and 4 alternatives were prepared with portable landscape designs. Most of the studies are focused on a single season, and both winter (January 2017) and summer (July 2017) seasons were evaluated in this study. In this context; ENVI-met analysis was made for the current situation and 4 different scenarios for both summer and winter months. In the climate analyzes made, air temperature, relative humidity, wind speed, Mean Radiant Temperature (MRT), Predicted Mean Vote (PMV) and Physiological Equivalent Temperature (PET) indexes were evaluated for 14:00, the hottest hour of the day. As a result of the evaluations; It has been revealed that city squares should not only have hard floors, but also green areas and other landscape design elements should be included in the squares. In addition, Alternative 4, which is a collective landscape design area in the middle of the square, gave the best results, reducing the PET value to 1.5 ℃ for January and 1.6 ℃ for July. As a result, thermal comfort increases as green space and landscape design elements are used in today's city squares.
The severity of urban heat islands (UHIs) is increasing due to global and urban climate change. The damage caused by UHIs is also increasing. To establish a plan to improve the deteriorating thermal environment in cities due to UHIs and to minimize the damage, further research is needed to accurately estimate and analyze the intensity and magnitude of UHIs. This systematic literature review (SLR) is an in-depth review of 51 studies obtained through a five-step filtering process focusing on their analysis of the spatial extent of UHIs, the UHI concept that was used for UHI estimation, and the UHI estimation and analysis methods. This SLR confirmed the need for accurate UHI intensity and magnitude estimation and analysis to reset the existing UHI classification based on the variety of vertical and horizontal ranges where UHIs occur. The results also indicated that the existing UHI energy concepts for estimating UHIs need to be modified and developed to reflect the three-dimensional physical form of the city. Finally, this SLR clarifies the need to develop an optimized analysis method for UHI research. The review results of this SLR will inform future studies and be the cornerstone for establishing policies and plans that can accurately predict and respond to the damage caused by UHIs.
Increasing heat-wave risk due to regional climate evolutions, exacerbated by urban heat island (UHI) effects, is a major threat for the inhabitants of many cities. Adaptive policies such as greening the urban environment are often proposed to limit population vulnerability, as vegetation enables to regulate the microclimate by evapotranspiration. The efficiency of such strategies depends on water availability and raises the issues of water supply for irrigation and of vegetation efficiency. Three vegetation watering alternatives and a scenario of pavement watering are studied and compared using Paris (France) urban area as a case study. With an evolution of the city based on “business as usual” trends, urban climate modeling enables to evaluate both UHI and heat stress under heat-wave conditions in 2100. Vegetation watering is efficient in reducing air temperature and thermal stress, but mostly in residential areas where vegetation density is important enough. Pavement watering is relevant in the densely built city center only where it improves the cooling efficiency and increases the water consumption by 2% only. The combination of both solutions provides the best performances with a reduction (compared to a non irrigated scenario) of the maximum temperature anomaly by 0.8 °C (2.6 °C) during the day (night).
The coupled processes of climate change and urbanization pose challenges for water resource management in cities worldwide. Comparing the vulnerabilities of water systems in Phoenix, Arizona and Portland, Oregon, this paper examines (1) exposures to these stressors, (2) sensitivities to the associated impacts, and (3) adaptive capacities for responding to realized or anticipated impacts. Based on a case study and survey-based approach, common points of vulnerability include: rising exposures to drier, warmer summers, and suburban growth; increasing sensitivities based on demand hardening; and limited capacities due to institutional and pro-growth pressures. Yet each region also exhibits unique vulnerabilities. Comparatively, Portland shows: amplified exposures to seasonal climatic extremes, heightened sensitivity based on less diversified municipal water sources and policies that favor more trees and other irrigated vegetation, and diminished adaptive capacities because of limited attention to demand management and climate planning for water resources. Phoenix exhibits elevated exposure from rapid growth, heightened sensitivities due to high water demands and widespread increases in residential and commercial uses, and limited adaptive capacities due to weak land use planning and "smart growth" strategies. Unique points of vulnerability suggest pathways for adapting to urban-environmental change, whether through water management or land planning. Greater coordination between the land and water sectors would substantially reduce vulnerabilities in the study regions and beyond.
In this paper a simple empirical scheme is presented, which gives hourly
estimates of the surface fluxes of heat and momentum from routine
weather data during daytime. The scheme is designed for grass surfaces,
but it contains parameters which take account of the surface properties
in general. The required input weather data are no more than a single
wind speed, air temperature at screen height and total cloud cover. The
output of the scheme is in terms of the Monin-Obukhov similarity
parameters; it is obtained by using estimates for the mean values of the
surface radiation and energy budget. For the climate of the Netherlands
good agreement is found between a full year of observations and
estimates made with the scheme. For all data it appears that
root-mean-square errors are = 90 W m2 for the incoming solar
radiation, = 63 W m2 for the net radiation, = 34 W
m2 for the sensible heat flux, = 0.01 m s1 for
the friction velocity and = 0.67 × 103 for the
similarity ratio between the surface roughness length and the Obukhov
stability parameter. A discussion is given an the surface parameters and
coefficients of the scheme.
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 I 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.
Estimates of incident solar radiation for the southwestern United States from 4 general circulation models (GCMs) are evaluated by comparison to observed values. Results indicate that GCMs reliably simulate the annual solar cycle, but generally underestimate incident solar rad~ation for the southwestern United States. For climatic conditions resulting from a doubling of atmospheric carbon dioxide, the 4 GCMs evaluated in this study estimate increases of 1 to 3 % of mean annual incident solar radiation simulated for current climatic conditions.
Two Long-Term Ecological Research (LTER) sites now include urban areas (Baltimore, Maryland and Phoenix, Arizona). A goal of LTER in these cities is to blend physical and social science investigations to better understand urban ecological change. Research monitoring programs are underway to investigate the effects of urbanization on ecosystems. Climate changes in these urban areas reflect the expanding population and associated land surface modifications. Long-term urban climate effects are detectable from an analysis of the GHCN (Global Historical Climate Network) database and a comparison of urban versus rural temperature changes with decadal population data. The relation of the urban versus rural minimum temperatures (Delta Tmin(u-r)) to population changes is pronounced and non-linear over time for both cities. The Delta Tmax(u-r) data show no well-defined temporal trends.
Solar radiation is the most important source of renewable energy available to reduce fossil CO2 atmospheric emissions and also is an important factor in heating, ventilation, and air conditioning (HVAC) energy considerations. Solar radiation may be affected by climate changes induced by CO2 emissions. In this study, a refined regional climate model was used to generate seasonal global radiation climatologies for the US under the present and mid 21st century enhanced atmospheric CO2 level. Simulated seasonal-mean daily global radiation (direct plus diffuse incident radiation on a horizontal surface) under the present climate showed overall reasonable agreement with observed patterns but with negative biases in most locations. In most of the US, the enhanced CO2 simulation (future climate) showed a trend of decreased seasonal-mean daily global radiation availability in the range of 0–20%. The most noticeable decrease was simulated in the western US during fall, winter, and spring. In small areas in the southern and northwestern US some increase in global radiation was simulated. Changes in global radiation during summer were relatively low.
The question about a possible dependence of the Urban Heat Island (UHI) on latitude and its causes has not been solved satisfactorily up to now. This paper tries to give an answer to the problem by extracting the UHI of cities on a global scale from the available international scientific literature and treating them with various statistical methods. In addition parameters like the city population, use of primary energy, topographic features, height above sea level and the energy balance of the earth's surface are included into the statistical calculations in order to substantiate a latitudinal variation of the UHI. Three main results could be derived from the statistical examinations, namely: 1. The UHI shows a trend to increase from low to high latitudes 2. The part of the observed variance of the UHI explained by its latitudinal variation, however, remains relatively small with about 6 %. 3. A statistically significant dependence of the UHI on latitude is based mainly on the latitudinal variation of anthropogenic heat production and radiation balance.
German
Die Frage nach einer möglichen Breitenabhängigkeit der städtischen Wärmeinsel (UHI) und deren Ursachen ist bis heute nicht zufriedenstellend beantwortet. Die vorliegende Publikation versucht zur Lösung des Problems beizutragen, indem aus der frei zugänglichen internationalen Fachliteratur Daten zur UHI von Städten im globalen Umfang entnommen und anschließend mit unterschiedlichen statistischen Methoden bearbeitet wurden. Parameter wie die Größe der Stadtpopulation, der Verbrauch an Primärenergie, topographische Merkmale, die Geländehöhe über dem Meeresspiegel und die Energiebilanz der Erdoberfläche werden in die statistischen Berechnungen miteinbezogen, um eine Breitenabhängigkeit der UHI zu untermauern. Die statistischen Untersuchungen führten zu drei wesentlichen Ergebnissen: 1. Die UHI zeigt die Tendenz einer Zunahme von niederen zu hohen Breiten. 2. Der Anteil der beobachteten Varianz der UHI, der durch ihre Breitenabhängigkeit erklärt wird, bleibt allerdings mit etwa 6 % relativ klein. 3. Eine statistisch signifikante Breitenabhängigkeit der UHI wird hauptsächlich durch eine Breitenvariation der anthropogenen Wärmeproduktion und der Strahlungsbilanz bedingt.
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 vege- tation 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 vali- dating 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. Keywords -- urban heat island (UHI), LUMPS model, scenarios, urban heat island mitigation, water resource planning Research Support: This work was supported by the National Science Foun- dation (NSF) under Grant SES-0345945 (Decision Center for a Desert City) and by the City of Phoenix Water Services Depart- ment. Any opinions, findings, and conclu- sions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF.
The effects of vegetation on human thermal stress in a hot-arid region were tested in two semi-enclosed urban spaces with various combinations of mature trees, grass, overhead shading mesh and paving. The index of thermal stress was calculated hourly from measured meteorological data in the studied sites to evaluate thermal comfort in the different spaces based on radiative and convective pedestrian–environment energy exchanges and sweat efficiency, and expressed on a thermal sensation scale ranging from ‘comfortable’ to ‘very hot’. The efficiency of water use in providing improved comfort was gauged for each of the vegetative landscaping treatments by comparing the total evapotranspiration with the reduction in thermal stress, both expressed in terms of their values in equivalent energy. While conditions in a paved, unshaded courtyard were found to be uncomfortable throughout the daytime hours (with half of these hours defined by severe discomfort), each of the landscape treatments made a clear contribution to improved thermal comfort. With shading, either by trees or mesh, discomfort was reduced in duration by over half and limited in maximum severity when the shading was placed above paving. When combined with grass, both shading mechanisms yielded comfortable conditions at all hours. In both cases, the effect of trees was more pronounced than that of the mesh, but by a small margin. With unshaded grass, ‘hot’ conditions in the courtyard were restricted to a short period in mid-afternoon, a considerable improvement over unshaded paving, attributable mainly to the lower radiant surface temperatures. Copyright © 2010 Royal Meteorological Society
For a significant number of urban hydrological issues, notably, water supply, water quality, groundwater recharge, saline intrusions, and flood runoff, knowledge of évapotranspiration (ET) rates is required. However, because little is known about the magnitude of urban ET rates and their spatial variability, broad assumptions have to be made in many applications. In this paper we present direct measurements of the magnitude and variability of ET rates using micrometeorological techniques (eddy correlation), in seven North American cities. The data demonstrate the importance of urban ET, and illustrate clear differences with land use. Simple relations between ET and measures of land cover are shown.
Accurate and reliable information on the spatial distribution of mangrove species is needed for a wide variety of applications, including sustainable manage-ment of mangrove forests, conservation and reserve planning, ecological and biogeographical studies, and invasive species management. Remotely sensed data have been used for such purposes with mixed results. Our study employed an object-oriented approach with the use of a lacunarity technique to identify different man-grove species and their surrounding land use and land cover classes in a tsunami-affected area of Thailand using Landsat satellite data. Our results showed that the object-oriented approach with lacunarity-transformed bands is more accurate (over-all accuracy 94.2%; kappa coefficient = 0.91) than traditional per-pixel classifiers (overall accuracy 62.8%; and kappa coefficient = 0.57).
This paper examines the impacts, feedbacks, and mitigation of the urban heat island in Phoenix, Arizona (USA). At Sky Harbor Airport, urbanization has increased the nighttime minimum temperature by 5C and the average daily temperatures by 3.1C. Urban warming has increased the number of misery hours per day for humans, which may have important social consequences. Other impacts include (1) increased energy consumption for heating and cooling of buildings, (2) increased heat stress (but decreased cold stress) for plants, (3) reduced quality of cotton fiber and reduced dairy production on the urban fringe, and (4) a broadening of the seasonal thermal window for arthropods. Climate feedback loops associated with evapotranspiration, energy production and consumption associated with increased air conditioning demand, and land conversion are discussed. Urban planning and design policy could be redesigned to mitigate urban warming, and several cities in the region are incorporating concerns regarding urban warming into planning codes and practices. The issue is timely and important, because most of the world's human population growth over the next 30 years will occur in cities in warm climates.
Through its various radiative effects and latent heat release, water plays a major role in the maintenance of climate. Therefore
a better understanding of climate and climate changes requires a better understanding of the hydrological cycle. In this study
we investigate the scale-decomposed atmospheric water budget over North America as simulated by the Canadian Regional Climate
Model (CRCM) driven by the Canadian Coupled Global Climate Model (CGCM) under current conditions for 1961–1990 and the SRES
A2 scenario for 2041–2070. A discrete cosine transform is applied to the atmospheric water budget variables in order to separate
small scales that are resolved exclusively by the high-resolution CRCM, from larger scales resolved by both the CRCM and low-resolution
driving CGCM. The moisture flux divergence is alternatively decomposed in terms of three scales of wind and humidity to provide
nine interaction terms. Statistics of these fields are calculated for winter and summer seasons, and the local statistical
significance of climate-change projections is tested. The contributions of each scale band to the water budget current climatology
and to its evolution in a warmer climate are investigated, addressing the issue of the potential added value of smaller scales.
Results show a time variability larger than the time mean for all variables, and a significant small-scale contribution to
time variability, which is even dominant in summer, both in the current and future climates. Future climate exhibits an overall
intensification of the hydrological cycle in winter, and more mixed changes in summer. Relative changes in the time mean and
time variability appear comparable, and the contribution of each scale band to variability changes remains overall very consistent
with their contribution to current climate variability.
KeywordsRegional climate model–Scale decomposition–Atmospheric water budget–Climate change–Added value
Variations in urban surface characteristics are known to alter the local climate through modification of land surface processes that influence the surface energy balance and boundary layer and lead to distinct urban climates. In Melbourne, Australia, urban densities are planned to increase under a new strategic urban plan. Using the eddy covariance technique, this study aimed to determine the impact of increasing housing density on the surface energy balance and to investigate the relationship to Melbourne's local climate. Across four sites of increasing housing density and varying land surface characteristics (three urban and one rural), it was found that the partitioning of available energy was similar at all three urban sites. Bowen ratios were consistently greater than 1 throughout the year at the urban sites (often as high as 5) and were higher than the rural site (less than 1) because of reduced evapotranspiration. The greatest difference among sites was seen in urban heat storage, which was influenced by urban canopy complexity, albedo, and thermal admittance. Resulting daily surface temperatures were therefore different among the urban sites, yet differences in above-canopy daytime air temperatures were small because of similar energy partitioning and efficient mixing. However, greater nocturnal temperatures were observed with increasing density as a result of variations in heat storage release that are in part due to urban canyon morphology. Knowledge of the surface energy balance is imperative for urban planning schemes because there is a possibility for manipulation of land surface characteristics for improved urban climates.
The Town Energy Balance (TEB) model of Masson simulates turbulent fluxes for urban areas. It is forced with atmospheric data and radiation recorded above roof level and incorporates detailed representations of the urban surface (canyon geometry) to simulate energy balances for walls, roads, and roofs. Here the authors evaluate TEB using directly measured surface temperatures and local-scale energy balance and radiation fluxes for two "simple" urban sites: a downtown area within the historic core of Mexico City, Mexico (stone buildings five to six stories in height), and a light industrial site in Vancouver, British Columbia, Canada (flat-roofed, single-story warehouse). At both sites, vegetation cover is less than 5%, which permits direct evaluation of TEB in the absence of a coupled vegetation scheme. Following small modifications to TEB, notably to the aerodynamic resistance formulations, the model is shown to perform well overall. In Mexico City, with deep urban canyons and stone walls, almost two-thirds of the net radiation is partitioned into storage heat flux during the day, and this maintains large heat releases and an upward turbulent sensible heat flux at night. TEB simulates all of these features well. At both sites TEB correctly simulates the net radiation, surface temperatures, and the partitioning between the turbulent and storage heat fluxes. The composite wall temperature simulated by TEB is close to the average of the four measured wall temperatures. A sensitivity analysis of model parameters shows TEB is fairly robust: for the conditions considered here, TEB is most sensitive to roof characteristics and incoming solar radiation.
Recent developments to the Local-scale Urban Meteorological Parameterization Scheme (LUMPS), a simple model able to simulate the urban energy balance, are presented. The major development is the coupling of LUMPS to the Net All-Wave Radiation Parameterization (NARP). Other enhancements include that the model now accounts for the changing availability of water at the surface, seasonal variations of active vegetation, and the anthropogenic heat flux, while maintaining the need for only commonly available meteorological observations and basic surface characteristics. The incoming component of the longwave radiation (L down arrow) in NARP is improved through a simple relation derived using cloud cover observations from a ceilometer collected in central London, England. The new L down arrow formulation is evaluated with two independent multiyear datasets (Lodz, Poland, and Baltimore, Maryland) and compared with alternatives that include the original NARP and a simpler one using the National Climatic Data Center cloud observation database as input. The performance for the surface energy balance fluxes is assessed using a 2-yr dataset (Lodz). Results have an overall RMSE <34 W m(-2) for all surface energy balance fluxes over the 2-yr period when using L down arrow as forcing, and RMSE < 43 W m(-2) for all seasons in 2002 with all other options implemented to model L down arrow.
A simple scheme to estimate net all-wave radiation (Q*) is evaluated using annual datasets in three urban settings (Chicago, Illinois; Los Angeles, California; and Łódź, Poland . Results are compared with a regression model based on incoming solar radiation and with an urban canopy-iayer model incorporating a canyon geometry radiation scheme that requires a larger set of meteorological and surface property inputs. This net all-wave radiation parameterization (NARP) is most sensitive to albedo and the effects of clouds on incoming longwave radiation. Although omitting the diurnal variation of albedo has little impact on overall model fit, its seasonal variability needs to be considered in some cases. For incoming longwave radiation. even clear-sky estimates show a large degree of scatter, and results degrade substantially if cloudy periods are included. NARP shows improvement over the regression approach. If observations of downwelling longwave radiation are included, NARP and the more complex canopy scheme show similar results, near or within the range of instrument error, depending of time of year.
This paper presents directly measured energy balance fluxes for suburban areas in four cities within the United States, Tucson, Sacramento, Chicago, and Los Angeles. They represent a range of synoptic regimes and surface morphologies (built and vegetative). Ensemble diurnal patterns and ratios of fluxes for clear, cloudy, and all sky conditions are presented. Consideration is given to both the mean and the variability of the fluxes. As expected, the magnitudes of the fluxes vary between cities; however, in general, the diurnal trends of flux partitioning are similar in terms of the timing of the peaks and changes in sign. Chicago is slightly different due to frequent wetting by rain. In the other cities, it seems that daytime Bowen ratios are inversely related to the area irrigated. -from Authors
The flux density of sensible heat to or from storage in the physical mass of the city is determined for seven cities (Chicago, Illinois; Los Angeles, California; Mexico City, Distrito Federal; Miami, Florida; Sacramento, California; Tucson, Arizona; and Vancouver, British Columbia) in North America across a 30°latitudinal range. These cities have a variety of synoptic-scale climates and surface cover and structural morphologies. In all cases the 'measured' storage heat flux is determined as the energy balance residual from direct observations of net all-wave radiation, and sensible and latent heat fluxes conducted using the same radiometer and eddy correlation techniques. Databases describing the surface characteristics around each site are developed from analysis of aerial photography and field surveys. Results indicate that storage heat flux is a significant component of the surface energy balance at all sites and is greatest at downtown and light industrial sites. Hysteresis behavior, of varying degrees, is seen at all locations. A simple objective hysteresis model (OHM), which calculates storage heat flux as a function of net all-wave radiation and the surface properties of the site, is found to perform well in the mean for most cases, with the notable exception of Tucson; but considerable scatter is observed at some sites. Some of this is attributed to the moisture, wind, and synoptic controls at each of the sites, and to hour-to-hour variability in the convective fluxes that the OHM does not simulate. Averaging over 2 to 3 h may be a more appropriate way to use the model. Caution should be used when employing the OHM in windy environments.
A linked set of simple equations specifically designed to calculate heat fluxes for the urban environment is presented. This local-scale urban meteorological parameterization scheme (LUMPS), which has similarities to the hybrid plume dispersion model (HPDM) scheme, requires only standard meteorological observations and basic knowledge of surface cover. LUMPS is driven by net all-wave radiation. Heat storage by the urban fabric is parameterized from net all-wave radiation and surface cover information using the objective hysteresis model (OHM). The turbulent sensible and latent heat fluxes are calculated using the available energy and are partitioned using the approach of de Bruin and Holtslag, and Holtslag and van Ulden. A new scheme to define the Holtslag and van Ulden α and β parameters for urban environments is presented: α is empirically related to the plan fraction of the surface that is vegetated or irrigated, and a new urban value of β captures the observed delay in reversal of the sign of the sensible heat flux in the evening. LUMPS is evaluated using field observations collected in seven North American cities (Mexico City, Mexico; Miami, Florida; Tucson, Arizona; Los Angeles and Sacramento, California; Vancouver, British Columbia, Canada; and Chicago, Illinois). Performance is shown to be better than that for the standard HPDM preprocessor scheme. Most improvement derives from the inclusion of the OHM for the storage heat flux and the revised β coefficient. The scheme is expected to have broad utility in models used to calculate air pollution dispersion and the mixing depths of urban areas or to provide surface forcing for mesoscale models of urban regions.
This paper describes a climatic analysis of landscape strategies for outdoor cooling in a hot-arid region, considering the efficiency of water use. Six landscape strategies were studied, using different combinations of trees, lawn, and an overhead shade mesh. The effects of these treatments were tested during the summer season in two semi-enclosed courtyards located at an urban settlement in the arid Negev Highlands of southern Israel. Compared to a non-vegetated exposed courtyard, which on average reached a maximum air temperature of 34 °C in mid-afternoon, a similar courtyard treated with shade trees and grass yielded a daytime temperature depression of up to 2.5 K, while shading the courtyard with a fabric shading mesh, counter-intuitively, caused a relative increase of nearly 1 K. Unshaded grass was found to cause only a small air temperature depression and had the highest water requirement. However when the grass was shaded, either by the trees or by the shade mesh, a synergic effect produced greater cooling as well as a reduction of more than 50% in total water use. The “cooling efficiency” of these strategies was calculated as the ratio between the sensible heat removed from the space and the latent heat of evaporation, with the latter representing the amount of water required for landscape irrigation. This measure is proposed as a criterion for evaluating landscape strategies in arid regions, where water resources are scarce.
A large number of urban surface energy balance models now exist with different assumptions about the important features of the surface and exchange processes that need to be incorporated. To date, no comparison of these models has been conducted; in contrast, models for natural surfaces have been compared extensively as part of the Project for Intercomparison of Land-surface Parameterization Schemes. Here, the methods and first results from an extensive international comparison of 33 models are presented. The aim of the comparison overall is to understand the complexity required to model energy and water exchanges in urban areas. The degree of complexity included in the models is outlined and impacts on model performance are discussed. During the comparison there have been significant developments in the models with resulting improvements in performance (root-mean-square error falling by up to two-thirds). Evaluation is based on a dataset containing net all-wave radiation, sensible heat, and latent heat flux observations for an industrial area in Vancouver, British Columbia, Canada. The aim of the comparison is twofold: to identify those modeling approaches that minimize the errors in the simulated fluxes of the urban energy balance and to determine the degree of model complexity required for accurate simulations. There is evidence that some classes of models perform better for individual fluxes but no model performs best or worst for all fluxes. In general, the simpler models perform as well as the more complex models based on all statistical measures. Generally the schemes have best overall capability to model net all-wave radiation and least capability to model latent heat flux.
The current Southwest drought is exceptional for its high temperatures and arguably the most severe in history. Coincidentally, there has been an increase in forest and woodland mortality due to fires and pathogenic outbreaks. Although the high temperatures and aridity are consistent with projected impacts of greenhouse warming, it is unclear whether the drought can be attributed to increased greenhouse gases or is a product of natural climatic variability. Climate models indicate that the 21st century will be increasingly arid and droughts more severe and prolonged. Forest and woodland mortality due to fires and pathogens will increase. Demography and food security dictate that water demand in the Southwest will remain appreciable. If projected population growth is twinned with suburb-centered development, domestic demands will intensify. Meeting domestic demands through transference from agriculture presents concerns for rural sustainability and food security. Environmental concerns will limit additional transference from rivers. It is unlikely that traditional supply-side solutions such as more dams will securely meet demands at current per-capita levels. Significant savings in domestic usage can be realized through decreased applications of potable water to landscaping, but this is a small fraction of total regional water use, which is dominated by agriculture. Technical innovations, policy measures, and market-based solutions that increase supply and decrease water demand are all needed. Meeting 21st-century sustainability challenges in the Southwest will also require planning, cooperation, and integration that surpass 20th-century efforts in terms of geographic scope, jurisdictional breadth, multisectoral engagement, and the length of planning timelines.
Thesis (Ph. D.)--Indiana University, 2003.
Remote sensing techniques have been shown effective for large-scale damagesurveys after a hazardous event in both near real-time or post-event analyses. The paperaims to compare accuracy of common imaging processing techniques to detect tornadodamage tracks from Landsat TM data. We employed the direct change detection approachusing two sets of images acquired before and after the tornado event to produce a principalcomponent composite images and a set of image difference bands. Techniques in thecomparison include supervised classification, unsupervised classification, and object-oriented classification approach with a nearest neighbor classifier. Accuracy assessment isbased on Kappa coefficient calculated from error matrices which cross tabulate correctlyidentified cells on the TM image and commission and omission errors in the result. Overall,the Object-oriented Approach exhibits the highest degree of accuracy in tornado damagedetection. PCA and Image Differencing methods show comparable outcomes. Whileselected PCs can improve detection accuracy 5 to 10%, the Object-oriented Approachperforms significantly better with 15-20% higher accuracy than the other two techniques.
The first measurements of the energy balance fluxes of a dry, densely built-up, central city site are presented. Direct observation of the net radiation, sensible and latent heat flux densities above roof-top in the old city district of Mexico City allow the heat storage flux density to be found by residual. The most important finding is that during daytime, when evaporation is very small (< 4% of net radiation), and therefore sensible heat uses dominate (Bowen ratio > 8), the uptake of heat by the buildings and substrate is so large (58%) that convective heating of the atmosphere is reduced to a smaller role than expected (38%), The nocturnal release of heat from storage is equal to or larger than the net radiation and sufficient to maintain an upward convective heat flux throughout most nights. It is important to see if this pattern is repeated at other central city, or dry urban sites, or whether it is only found in districts dominated by massive stone structures. These findings have implications for the height of the urban mixing layer and the magnitude of the urban heat island.
The current Southwest drought is exceptional for its high temperatures and arguably the most severe in history. Coincidentally, there has been an increase in forest and woodland mortality due to fires and pathogenic outbreaks. Although the high temperatures and aridity are consistent with projected impacts of greenhouse warming, it is unclear whether the drought can be attributed to increased greenhouse gasses or is a product of natural climatic variability. Climate models indicate that the 21st century will be increasingly arid and droughts more severe and prolonged. Forest and woodland mortality due to fires and pathogens will increase. Demography and food security dictate that water demand in the Southwest will remain appreciable. If projected population growth is twinned with suburb-centered development, domestic demands will intensify. Meeting domestic demands through transference from agriculture presents concerns for rural sustainability and food security. Environmental concerns will limit additional transference from rivers. It is unlikely that traditional supply-side solutions such as more dams will securely meet demands at current per-capita levels. Significant savings in domestic usage can be realized through decreased applications of potable water to landscaping, but this is a small fraction of total regional water use, which is dominated by agriculture. Technical innovations, policy measures, and market-based solutions that increase supply and decrease water demand are all needed. Meeting 21st-century sustainability challenges in the Southwest will also require planning, cooperation, and integration that surpass 20th-century efforts in terms of geographic scope, jurisdictional breadth, multisectoral engagement, and the length of planning timelines.
Previous studies have shown that residential water consumption in Phoenix, Arizona is significantly related to changes in climate, although that sensitivity varies substantially from one census tract to another. In this investigation, we determine the empirical relationship between water consumption and variations in temperature and precipitation. We find the sensitivity of water consumption to either climate variable is positively related to the percent of land covered in mesic irrigated landscaping, mean household income, lot size, and percent of single-family residential lots containing swimming pools. We use estimated changes in temperature and precipitation for 50 model-scenario combinations presented by the IPCC, and we determined that mean water consumption should increase by an average of over 3% by ~2050, but the climate-induced change in consumption varies considerably across census tracts.
This article presents a study of residential parcel design and surface heat island formation in a major metropolitan region of the southeastern United States. Through the integration of high-resolution multispectral data (10m) with property tax records for over 100,000 single-family residential parcels in the Atlanta, Georgia, metropolitan region, the influence of the size and material composition of residential land use on an indicator of surface heat island formation is reported. In contrast to previous work on the urban heat island, this study derives a parcel-based indicator of surface warming to permit the impact of land use planning regulations governing the density and design of development on the excess surface flux of heat energy to be measured. The results of this study suggest that the contribution of individual land parcels to regional surface heat island formation could be reduced by approximately 40% through the adoption of specific land use planning policies, such as zoning and subdivision regulations, and with no modifications to the size or albedo of the residential structure.
Surface evaporation is an important component of the urban energy balance, and its role in arid-zone cities may significantly differ from that observed in more temperate regions. However, the quantification of evapotranspiration is difficult in a complex urban setting, given the heterogeneity of the terrain and its various dry and wet elements. Here an open-air scaled urban surface (OASUS) is employed to quantify latent heat flux as a function of the surface area available for evaporation and the three-dimensional (3-D) urban geometry. The OASUS model consists of an extensive urban-like building/street array located in an arid Negev region of southern Israel (30.8°N, 480 m above sea level). Measurements were carried out during the summer month of August, and flux partitioning was analysed using evaporation pans of varying surface areas embedded in arrays of varying height. Results indicated that the increase in latent heat removal with respect to equivalent ‘vegetative’ surface area was nearly linear. Increasing latent heat flux with ‘vegetated fraction’ was offset in approximately equal measure by decreases in storage and turbulent sensible heat flux. The proportion of the radiant energy budget represented by evaporative heat loss was also linked to the 3-D geometry of the array, increasing linearly with the ratio between vegetative cover and the ‘complete’ urban surface area. Copyright © 2008 Royal Meteorological Society
A model is developed for the energy balance of an urban area, represented as a sequence of two‐dimensional street canyons. The model incorporates a novel formulation for the sensible‐heat flux, that has previously been validated against wind tunnel models, and a formulation for radiation that includes multiple reflections and shadowing. This energy balance model is coupled to a model for the atmospheric boundary layer. Results are analysed to establish how the physical processes combine to produce the observed features of urban climate, and to establish the roles of building form and fabric on the urban modification to climate.
Over a diurnal cycle there are morning and evening transition periods when the net flux of radiation is largely balanced by the flux of heat into the surface. The urban surface has a large surface area in contact with the air, and hence a large active heat capacity, and so the urban area needs to absorb a larger amount of heat than a rural area to change the surface temperature. The morning and evening transitions are therefore prolonged over urban areas, delaying the onset of convective or stable boundary layers after sunrise and sunset. The model shows that the energy balance of the roof behaves very differently from the combined energy balance of the street canyon system of walls and street. The sensible‐heat flux from the street canyon into the boundary layer is increased by the increased surface area, but is decreased by the buildings reducing the local flow speeds. The net result is that, for the two‐dimensional geometry investigated here, the sensible‐heat flux from the canyon is not strongly sensitive to canyon geometry. The sensible‐heat flux from the roof is larger than from the street, and so the total sensible‐heat flux into the boundary layer, and hence also the air temperature, is strongly dependent on the fraction of plan area occupied by roofs. The radiation budget of the street canyon, which largely drives the temperatures of the canyon surfaces, is significantly changed by the limited sky view and multiple reflections caused by the local building form. The canyon surface temperatures thus depend strongly on local building morphology.
Finally, two mechanisms are suggested for how urban areas might maintain a positive sensible‐heat flux at night. Firstly, if the roof material has much lower heat capacity than the street canyon surfaces, then the roof can cool the boundary‐layer air faster than the street canyon surfaces cool, leading to a positive heat flux out of the street canyon. Secondly, advection decouples the boundary layer from the local surface energy balance. In this way, cool air, perhaps from a rural area, advected on to an urban surface can lead to a positive sensible‐heat flux which then tends to neutralize any stable stratification in the boundary layer. Copyright © 2006 Royal Meteorological Society
As recently as 1950, 30% of the world's population lived in urban areas. By the year 2030, 60% of the world's population will live in cities, according to the United Nations (2001) World Population Prospects Revision Report. Urbanization is quickly transitioning communities from the natural rural vegetation to man-made urban engineered infrastructure. The anthropogenic-induced change has manifested itself in microscale and mesoscale increases in temperatures in comparison to adjacent rural regions which is known as the urban heat island (UHI) effect and results in potentially adverse consequences for local and global communities. One of the great challenges facing our current generation of scientists and engineers is how to support the growth of the new and existing arid urban centers in a sustainable manner. This is even more pronounced in arid regions, which will sustain the greatest rate of urbanization. This paper is focused on understanding the interdependency of the infrastructure used to support the growth of urban regions and their environmental, social and economic consequences with an emphasis on the rapidly urbanizing arid region of Phoenix, Arizona.
Results from an experimental network of seven energy balance stations in and around a European city are presented. The network of micrometeorological stations was part of the Basel Urban Boundary Layer Experiment (BUBBLE) carried out in the city of Basel, Switzerland. Three urban sites provided turbulent flux densities and radiation data over dense urban surfaces. Together with a suburban site and three rural reference sites, this network allowed the simultaneous comparison of urban, suburban, and rural energy balance partitioning during one month of summertime measurements. The partitioning is analysed together with long-term data to evaluate the magnitude of the urban flux density modification, and to document characteristic values in their diurnal and yearly course. Simple empirical relations between flux densities and surface characteristics are presented. The energy balance partitioning is addressed separately for daytime and nocturnal situations. All four components of the surface radiation budget are analysed. Moreover, the vertical flux density divergences within the urban canopy layer are discussed. Copyright 2004 Royal Meteorological Society.
In using traditional digital classification algorithms, a researcher typically encounters serious issues in identifying urban land cover classes employing high resolution data. A normal approach is to use spectral information alone and ignore spatial information and a group of pixels that need to be considered together as an object. We used QuickBird image data over a central region in the city of Phoenix, Arizona to examine if an object-based classifier can accurately identify urban classes. To demonstrate if spectral information alone is practical in urban classification, we used spectra of the selected classes from randomly selected points to examine if they can be effectively discriminated. The overall accuracy based on spectral information alone reached only about 63.33%. We employed five different classification procedures with the object-based paradigm that separates spatially and spectrally similar pixels at different scales. The classifiers to assign land covers to segmented objects used in the study include membership functions and the nearest neighbor classifier. The object-based classifier achieved a high overall accuracy (90.40%), whereas the most commonly used decision rule, namely maximum likelihood classifier, produced a lower overall accuracy (67.60%). This study demonstrates that the object-based classifier is a significantly better approach than the classical per-pixel classifiers. Further, this study reviews application of different parameters for segmentation and classification, combined use of composite and original bands, selection of different scale levels, and choice of classifiers. Strengths and weaknesses of the object-based prototype are presented and we provide suggestions to avoid or minimize uncertainties and limitations associated with the approach.
This paper reviews methods that have been used to evaluate global climate simulations and to downscale global climate scenarios for the assessment of climate impacts on hydrologic systems in the Pacific Northwest, USA. The approach described has been developed to facilitate integrated assessment research in support of regional resource management. Global climate model scenarios are evaluated and selected based on historic 20th century simulations. A statistical downscaling method is then applied to produce a regional data set. To facilitate the use of climate projections in hydrologic assessment, additional statistical mapping may be applied to generate synthetic station time series. Finally, results are presented from a regional climate model that indicate important differences in the regional climate response from what is captured by global models and statistical downscaling. Copyright © 2007 Royal Meteorological Society
Over the last 50 years the developing world, much of which is located in (sub)tropical regions, has seen a dramatic growth of its urban population associated with serious degradation of environmental quality. The total number of (sub)tropical urban climate studies, however; is still small (<20% of all urban climate studies). The available work is further biased towards descriptive studies rather than process work that seeks to indicate the physical climatology of (sub)tropical cities. The available results allow for a preliminary comparison with data from temperate latitudes. Urban heat island (UHI) intensities are generally lower compared to those of temperate cities with comparable population and show a seasonal variation with lower (higher) intensities during the wet (dry) season. (Sub)tropical population-based relations may exist but insufficient appropriate data is available to confirm a logarithmic relationship or systematic differences between different climate types. The (sub)tropical energy balance studies are biased towards dry, clear sky conditions. The amount of net radiation dissipated by sensible heat during daytime is about 40% which is similar to values observed in (sub)urban areas of cities located in temperate climates. Energy partitioning is modulated by water availability and higher percentage of vegetation promotes latent heat flux at the expense of surface heat storage. The apparent strong influence of vegetation and water availability on the energy partitioning irrespective of the climate type, suggests vegetation to be an effective means to reduce heat storage uptake during daytime and hence has the potential to effectively mitigate the nocturnal heat island. It is important to ensure that the rapidly expanding cities of the developing world incorporate climatological concerns in their design to provide a better living and working environment for a large segment of the world's inhabitants. Copyright © 2007 Royal Meteorological Society
The urban thermal environment varies not only from its rural surroundings but also within the urban area due to intra-urban
differences in land-use and surface characteristics. Understanding the causes of this intra-urban variability is a first step
in improving urban planning and development. Toward this end, a method for quantifying causes of spatial variability in the
urban heat island has been developed. This paper presents the method as applied to a specific test case of Portland, Oregon.
Vehicle temperature traverses were used to determine spatial differences in summertime ~2m air temperature across the metropolitan
area in the afternoon. A tree-structured regression model was used to quantify the land-use and surface characteristics that
have the greatest influence on daytime UHI intensity. The most important urban characteristic separating warmer from cooler
regions of the Portland metropolitan area was canopy cover. Roadway area density was also an important determinant of local
UHI magnitudes. Specifically, the air above major arterial roads was found to be warmer on weekdays than weekends, possibly
due to increased anthropogenic activity from the vehicle sector on weekdays. In general, warmer regions of the city were associated
with industrial and commercial land-use. The downtown core, whilst warmer than the rural surroundings, was not the warmest
part of the Portland metropolitan area. This is thought to be due in large part to local shading effects in the urban canyons.
Urbanization related alterations to the surface energy balance impact urban warming ('heat islands'), the growth of the boundary layer, and many other biophysical processes. Traditionally, in situ heat flux measures have been used to quantify Such processes, but these typically represent only a small local-scale area within the heterogeneous urban environment. For this reason, remote sensing approaches are very attractive for elucidating more spatially representative information. Here we use hyperspectral imagery from a new airborne sensor, the Operative Modular Imaging Spectrometer (OMIS), along with a survey map and meteorological data, to derive the land cover information and surface parameters required to map spatial variations in turbulent sensible heat flux (Q(H)). The results from two spatially-explicit flux retrieval methods which use contrasting approaches and, to a large degree, different input data are compared for a central urban area of Shanghai, China: (1) the Local-scale Urban Meteorological Parameterization Scheme (LUMPS) and (2) an Aerodynamic Resistance Method (ARM). Sensible heat fluxes are determined at the full 6 m spatial resolution of the OMIS sensor, and at lower resolutions via pixel exceeds that of roads, water and vegetated areas, with values peaking at similar to 350 W m(-2), whilst the storage heat flux is greatest for road dominated pixels (peaking at around 420 W m(-2)). We investigate the use of both OMIS-derived land surface temperatures made using a Temperature-Emissivity Separation (TES) approach, and land surface temperatures estimated from air temperature measures. Sensible heat flux differences from the two approaches over the entire 2 x 2 km study area are less than 30 W m(-2), suggesting that methods employing either strategy maybe practical when operate using low spatial resolution (e.g. 1 km) data. Due to the differing methodologies, direct comparisons between results obtained with the LUMPS and ARM methods are most sensibly made at reduced spatial scales. At 30 m spatial resolution, both approaches produce similar results, with the smallest difference being less than 15 W m(-2) in mean Q(H) averaged over the entire study area. This is encouraging given the differing architecture and data requirements of the LUMPS and ARM methods. Furthermore, in terms of mean study Q(H,) the results obtained by averaging the original 6 m spatial resolution LUMPS-derived Q(H) values to 30 and 90 m spatial resolution are within similar to 5 W m(-2) of those derived from averaging the original surface parameter maps prior to input into LUMPS, suggesting that that use of much lower spatial resolution spaceborne imagery data, for example fro Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is likely to be a practical solution for heat flux determination in urban areas. Crown Copyright
The study was conducted in a suburb of Vancouver, British Columbia, from January to June 1987. It included hourly measurements of net all-wave radiation, sensible heat flux and the Bowen ratio. The anthropogenic and storage heat fluxes were modelled. A dynamic source area model was employed to ensure the modelled parameters were consistent spatially with the measured turbulent fluxes. The winter-spring urban energy blances observed in this study are different to those reported for summertime conditions at the same site. The fluxes for the entire period are not symmetrical about solar noon. Hence earlier interpretations possibly should be modified. Apart from this feature the spring season balances are similar to those reported for the summertime in terms of relative importance of individual fluxes. The wintertime energy balance appears to be different to that of spring and summer. -from Author
Surface properties, such as roughness and vegetation, which vary both within and between urban areas, play a dominant role in determining surface-atmosphere energy exchanges. The turbulent heat flux partitioning is examined within a single urban area through measurements at four locations in Łódź, Poland, during August 2002. The dominant surface cover (land use) at the sites was grass (airport), 1-3-story detached houses with trees (residential), large 2-4-story buildings (industrial), and 3-6-story buildings (downtown). However, vegetation, buildings, and other "impervious" surface coverage vary within some of these sites on the scale of the turbulent flux measurements. Vegetation and building cover for Łódź were determined from remotely sensed data and an existing database. A source-area model was then used to develop a lookup table to estimate surface cover fractions more accurately for individual measurements. Bowen ratios show an inverse relation with increasing vegetation cover both for a site and, more significant, between sites, as expected. Latent heat fluxes at the residential site were less dependent on short-term rainfall than at the grass site. Sensible heat fluxes were positively correlated with impervious surface cover and building intensity. These results are consistent with previous findings (focused mainly on differences between cities) and highlight the value of simple measures of land cover as predictors of spatial variations of urban climates both within and between urban areas.
An objective hysteresis model to predict the storage heat flux in urban areas is presented. A review of observational and theoretical work reveals this approach to be more appropriate than the linear relation between soil heat flux and net all-wave radiation. A scheme to implement the model in any urban area is developed. In essence the model only requires land cover and net all-wave radiation as input, but it can be further refined to include anthropogenic heat release, the three-dimensional form of the surface, and can allow for changes in source area. Tests against energy balance data from a site in Vancouver, BC indicate the model simulates most aspects of measured storage heat flux values for a suburban site in both winter and summer. Comparison with the results of a study in Bonn, Germany involving the use of heat flux plates and detailed heat content change calculations gives good agreement except for a phase difference of about 1 h. There is evidence to suggest that the spatial variation of intra-urban heat storage may be relatively conservative.
The microclimates of a suburban Colorado residential landscape were studied to examine the effect of design decisions on temperature, wind speed, and relative humidity. On a hot day typical of summer, vegetated landscape elements were several degrees cooler throughout the day than non-vegetated surfaces. Across the development, dry, native grass landscapes were warmer than irrigated greenbelts and irrigated residential lawns. These data demonstrate the importance of evapotranspiration as a cooling agent in the dry, semi-arid Colorado environment. Extended meteorological measurements throughout the summer suggested housing density created microclimatic differences in the development. Heat generated by built landscape elements was readily vented from a porous neighborhood but not in a denser neighborhood. This study demonstrates that in the semi-arid Colorado environment, the choice of planting material, the design of irrigated greenbelts within a community, and the density of housing all have important consequences in creating thermally-pleasing environments.
Human exposure to excessively warm weather, especially in cities, is an increasingly important public health problem. This study examined heat-related health inequalities within one city in order to understand the relationships between the microclimates of urban neighborhoods, population characteristics, thermal environments that regulate microclimates, and the resources people possess to cope with climatic conditions. A simulation model was used to estimate an outdoor human thermal comfort index (HTCI) as a function of local climate variables collected in 8 diverse city neighborhoods during the summer of 2003 in Phoenix, USA. HTCI is an indicator of heat stress, a condition that can cause illness and death. There were statistically significant differences in temperatures and HTCI between the neighborhoods during the entire summer, which increased during a heat wave period. Lower socioeconomic and ethnic minority groups were more likely to live in warmer neighborhoods with greater exposure to heat stress. High settlement density, sparse vegetation, and having no open space in the neighborhood were significantly correlated with higher temperatures and HTCI. People in warmer neighborhoods were more vulnerable to heat exposure because they had fewer social and material resources to cope with extreme heat. Urban heat island reduction policies should specifically target vulnerable residential areas and take into account equitable distribution and preservation of environmental resources.
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