•Urbanization effects are expressed as the urban climate and land cover change.•The land cover change effect is recognized as the major effect.•Land cover change effect is stable in time ...series.•Urban climate effect has experienced an increasing trend for the past two decades.
Rapid urbanization leads to changes in the thermal characteristics of urban areas. Despite cities serving as natural laboratories to investigate responses to global change, it remains unclear how urbanization affects the thermal environment during global warming. Urbanization effects can be categorized as either the effect of urban climate (UCE) or land cover change (LCCE). This study proposes a conceptual framework for separating the urbanization effects on the thermal environment in 29 major Chinese cities. Results show that land surface temperature increases with impervious surface fractions in the urban area and decreases with vegetation fractions in rural areas, resulting in significant UCE and LCCE across cities, with LCCE approximately 1.3 to 5.7 times greater than UCE. These findings provide a comprehensive understanding of the thermal environment change caused by urbanization. To mitigate the negative effects of urbanization on the thermal environment, reducing land cover change would be more effective.
Transformative capacity (TC) is key for addressing climate change impacts. It refers to urban areas’ ability for profound and intentional change to address current challenges and move towards a more ...desirable and resilient state. However, its varied applications across disciplines can lead to misunderstandings and implementation challenges. Thus, this Semi-Systematic Literature Review (SSLR) on TC within urban studies from 2016 to 2022 aims to overview and synthesise TC literature and its gaps to inform ongoing debates, intersecting it with climate-related research. The results show an increasing interest in TC within two fields of knowledge: resilience studies and transformative research. The review found TC as a catalyst for transformative actions, promoting sustainable pathways, enhancing resilience, and driving fundamental changes in urban climate adaptation. Finally, the prevailing literature gaps concern the TC concept’s fragmentation, excessive research on governance features, and lack of joint research about TC and innovation.
Sealed surfaces greatly influence Urban Heat Island (UHI) effects. In this respect, both the composition and spatial patterns of anthropogenic land use play an important role in local thermal ...pattern. The urban environments' climate change adaptation strategy needs adequate knowledge systems urban planners can use to organise and design more resistant and resilient urban spaces. This study examined the relationship between Land Surface Temperature (LST) variations and increasing urbanised areas during the period 2001–2011 in the Po Valley, utilising different urban growth spatial patterns (UGSP). Remotely sensed LST data was obtained from MODIS (MODerate Resolution Imaging Spectroradiometer) at a resolution of 1 km/pixel for an 11 year-period, from 2001 to 2011, with urbanisation data from the ISTAT map (nominal scale 1:10,000) respectively for the 2001 and 2011 time sections. The relationship between dependent (mean annual daytime, nighttime and daily values) and independent (urbanised areas) variables were investigated through ANOVA test and post-hoc analysis (p < 0.01) for all defined UGSP. Results showed that there is a decreasing LST range (in all conditions) associated with progressive increase of urbanised areas. Furthermore, clustered patterns urban growth have a statistically significant relationship with daytime, nighttime and daily conditions while dispersed pattern urban growth have the same with nighttime only. The outcomes are helpful for understanding the effects of different UGSP, which have significant implications for urban planning, and identifying the critical territorial sectors in need of sustainable mitigation actions.
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•Between 2001 and 2011, the Po Valley area saw an increase of 630 km2 in urban areas.•The prevailing model of urban growth is the UDI 0 (aggregated urban growth).•The LST in daytime conditions was an average increase of +1,36 °C in the study area.•Quantitative framework between increased urbanised areas and LST change performed.•The UDI + (urban dispersion) shows an increase in the minimum differential recorded.
•Anthropogenic heat (AH) from buildings in Los Angeles County was simulated and analyzed.•AH has high variabilities in diurnal and season profiles across urban areas.•AH from building exterior ...surfaces is the largest component.•HVAC-related AH can increase daytime and nighttime urban air temperature by up to 0.6 °C and 2.9 °C, respectively.•The AH dataset at the annual hourly resolution and three spatial levels was published.
Anthropogenic heat (AH), i.e., waste heat from buildings to the ambient environment, increases urban air temperature and contributes to the urban heat island effect, which leads to more air-conditioning energy use and higher associated waste heat during summer, forming a positive feedback loop. This study used a bottom-up simulation approach to develop a dataset of the annual hourly AH profiles for 1.7 million buildings in Los Angeles (LA) County for the year 2018 aggregated at three spatial resolutions: 450 m, 12 km, and the census tract. Building AH exhibits strong seasonal and diurnal patterns, as well as large spatial variations across the urban areas. Building AH peaks in May and reaches a maximum of 878 W/m2 within one of several AH hotspots in the region. Among the three major AH components (surface convection, heat rejection from HVAC systems, and zonal air exchange), the surface convection component is the largest, accounting for 78% of the total building AH across LA County. Higher AH is attributed to large building density, a high percentage of industrial buildings, and older building stock. While AH peaks during the day, the resulting ambient temperature increases are much larger during the night. During the July 2018 heatwave in LA County, building AH (excluding the surface component) leads to a daily maximum ambient temperature increase of up to 0.6 °C and a daily minimum ambient temperature increase of up to 2.9 °C. It is recommended that reducing summer building AH should be considered by policy makers in developing mitigation measures for cities to transition to clean energy while improving heat resilience.
This research evaluates the perception of human thermal sensation in the Mediterranean climate in an attempt to calibrate the scale of human thermal sensation for this climate, by applying the ...Physiologically Equivalent Temperature (PET) index. A field survey was conducted in the city of Tel Aviv, Israel in several outdoor urban spaces during summers and winters of 2007–2011. Empirical data of climatic variables were collected by meteorological stations and accompanied by subjective thermal sensation questionnaires. The relations between the calculated PET values for the investigated sites and the Thermal Sensation Vote (TSV) were examined. Analytical results indicate that the “neutral” TSV range for the Mediterranean climate is between 20 and 25 °C PET, higher than that of the temperate climates and lower than that of the hot and humid climates. The PET boundaries for the cold classes of thermal perception in the Mediterranean are relatively high in comparison to Western/Middle Europe but are relatively low in comparison to Taiwan. However, the differences in PET boundaries for the hot classes of thermal perception decrease as the temperature values increase, toward an almost identical definition of “very hot” in Western/Middle Europe, the Mediterranean and Taiwan.
► This research aims to adjust the PET index to Coastal Mediterranean climate. ► The definition of thermal sensation scale is subject to local adaptation. ► Upper boundary of human thermal comfort is similar in different climatic areas. ► Lower boundary of human thermal comfort is divergent in different climatic areas.
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 (U.S.) with the Weather Research and Forecasting model coupled to a multilayer building energy scheme. The performance of the modeling system is evaluated against 10 Arizona Meteorological Network weather stations and one weather station maintained by the National Weather Service 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.
Key Points
AC systems increased the mean air temperature over 1°C in some urban locations
Waste heat from AC improved the air temperature correspondence to observations
Releasing waste heat into the ambient environment increases cooling demands
Modeling results incorporating several distinct urban expansion futures for the United States in 2100 show that, in the absence of any adaptive urban design, megapolitan expansion, alone and separate ...from greenhouse gas-induced forcing, can be expected to raise near-surface temperatures 1–2 °C not just at the scale of individual cities but over large regional swaths of the country. This warming is a significant fraction of the 21st century greenhouse gas-induced climate change simulated by global climate models. Using a suite of regional climate simulations, we assessed the efficacy of commonly proposed urban adaptation strategies, such as green, cool roof, and hybrid approaches, to ameliorate the warming. Our results quantify how judicious choices in urban planning and design cannot only counteract the climatological impacts of the urban expansion itself but also, can, in fact, even offset a significant percentage of future greenhouse warming over large scales. Our results also reveal tradeoffs among different adaptation options for some regions, showing the need for geographically appropriate strategies rather than one size fits all solutions.
Urban trees ameliorate heat stress for urban dwellers. However, it is difficult to quantitatively assess the integrated impacts of tree planting and street layouts on visual and thermal comfort in ...simulations and urban field experiments. We conducted scaled outdoor experiments in Guangzhou to investigate the influence of tree plantings on pedestrian visual and thermal comfort in street canyons with various aspect ratios (H/W = 1, 2, 3; H = 1.2 m). We considered the effects of tree crown covers (big and small crown) and tree planting densities (ρ = 1, 0.5) on pedestrian illuminance level and two thermal comfort indices (Physiological Equivalent Temperature: PET and Index of Thermal Stress: ITS).
When ρ = 1, trees in most cases reduce pedestrian illuminance (maximum 140.0klux) and improve visual comfort. Decreasing ρ from 1 to 0.5 increases the illuminance (maximum 179.5klux) in the streets with big crown trees (H/W = 1, 2) and in the street with small crown trees (H/W = 2). When ρ = 1 (H/W = 1, 2), big crown trees decrease the peak daytime PET (by about 4.0 °C) and ITS (by about 285 W). Small crown trees (ρ = 1, H/W = 1, 2) produce a warming effect on peak daytime PET (2.0-3.0 °C), but a reduction in ITS is observed when H/W = 2, 3. After reducing ρ from 1 to 0.5, big crown trees increase peak daytime thermal stress according to both indices when H/W = 1, 2. Small crown trees exhibit a similar PET cycle between ρ = 0.5 and ρ = 1 across various H/W, but their daytime reduction of ITS is less effective when ρ = 0.5 (H/W = 2). The discrepancies between PET and ITS are attributed to their different approaches to modelling radiation fluxes. The narrower the street, the lower the illuminance, PET, and ITS, while their increases caused by reduced ρ are limited in narrow streets. Our study informs some potential urban tree planting strategies and produces high-quality validation data for numerical simulations and theoretical models.
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•Scaled outdoor experiments are tested for tree impacts in streets (H/W = 1–3, H = 1.2 m).•Tree plantings reduce pedestrian illuminance by up to 140 klux.•Big crown trees reduce daytime PET (4.0 °C) and ITS (285 W) to improve thermal comfort.•Big crown trees increase PET and ITS as planting density reduces (ρ = 1 to ρ = 0.5).•During daytime, small crown trees reduce ITS but increase PET.
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•We quantified the relationship between urban forms and thermal comfort.•Our CFD and thermal comfort models were validated by measurements.•Our coupled model produced comparable Tmrt ...and sensible PET relative to other studies.•Predicted PETs at noon were more than 10 °C relative to the morning within buildings.•Modifications of building lengths and porosity were keys to reduce heat stresses.
Urban compact buildings impose large frictional drag on boundary-layer air flow and create stagnant air within the building environment. It results in exacerbating the street-level outdoor thermal comfort (OTC). It is common to perform in-situ measurements of the OTC in different urban forms and to study their relationship. However, it is impossible to do so from a planning perspective because of the absence of physical planned urban forms. Our objective was to quantify the thermal environment and OTC in different planned complex urban forms by well-validated numerical models. We coupled a computational fluid dynamics (CFD) model to an OTC (Rayman) model to study the OTC. The κ–ω SST turbulent model was adopted for the CFD simulations, with accuracy of the turbulent model validated by wind tunnel measurements. The highest calculated air temperature within the street canyon of a planned bulky urban form could reach more than 5 °C higher than the surrounding environment. Within the tested urban forms, our coupled model predicted mean radiant temperature comparable with measurements in the literature. The model also produced sensible street-level physiologically equivalent temperatures (PETs) when comparing with those listed in the human thermal sensation categories. In the morning, the predicted PETs within all the urban forms were lower than that in open areas, which indicated that the shading of buildings effectively reduced the PET increase due to solar irradiance. At noon, increases in PETs by more than 10 °C relative to the morning situation indicated that when the buildings acted as heat sources after insolation absorption, increase in the air temperature at the street intersection and in the street canyon made an important contribution to the receiver PETs. The reduction in building lengths and increase in the low-level porosity were the most effective ways to reduce the heat stress at the pedestrian-level.
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