Synergies between Urban Heat Island and Urban Heat Wave Effects in 9 Global Mega–Regions from 2003 to 2020

Global urbanization significantly impacts the thermal environment in urban areas, yet urban heat island (UHI) and urban heat wave (UHW) studies at the mega–region scale have been rare, and the impact study of urbanization is still lacking. In this study, the MODIS land surface temperature (LST) product was used to depict the UHI and UHW in nine mega–regions globally between 2003 and 2020. The absolute and percentile–based UHW thresholds were adopted for both daily and three–day windows to analyze heat wave frequency, and UHW magnitude as well as frequency were compared with UHI variability. Results showed that a 10% increase in urban built-up density led to a 0.20 °C to 0.95 °C increase in LST, a 0.59% to 7.17% increase in hot day frequency, as well as a 0.08% to 0.95% increase in heat wave number. Meanwhile, a 1 °C increase in UHI intensity (the LST differences between the built-up and Non-built-up areas) led to a 2.04% to 92.15% increase in hot day frequency, where daytime LST exceeds 35 °C and nighttime LST exceeds 25 °C, as well as a 3.30% to 33.67% increase in heat wave number, which is defined as at least three consecutive days when daily maximum temperature exceeds the climatological threshold. In addition, the increasing rates of UHW magnitudes were much faster than the expansion rates of built-up areas. In the mega–regions of Boston, Tokyo, São Paulo, and Mexico City in particular, the increasing rates of UHW hotspot magnitudes were over 2 times larger than those of built-up areas. This indicated that the high temperature extremes, represented by the increase in UHW frequency and magnitudes, were concurrent with an increase in UHI under the context of climate change. This study may be beneficial for future research of the underlying physical mechanisms on urban heat environment at the mega–region scale.

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Impact of mass human migration during Chinese New Year on Beijing urban heat island

10.5194/egusphere-egu2020-6250 ◽

2020 ◽

Author(s):

Jingjing Dou ◽

Shiguang Miao

Keyword(s):

Spatial Distribution ◽

Urban Heat Island ◽

Human Migration ◽

Floating Population ◽

Maximum Temperature ◽

Daily Maximum Temperature ◽

Daily Maximum ◽

Heat Island ◽

Urban Heat ◽

The Impact

<p>The Chinese New Year (CNY, also called Spring Festival), which officially lasts for 7 days, is the most important holiday in China. Chinese people in large cities usually return to their hometowns for family reunions before the CNY holiday and return afterward. Nearly half of Beijing&#8217;s population has been reported to leave the city for family reunions before the CNY holidays in the past several years. Hourly automatic weather station (AWS) data during CNY 2010-2015 were used to analyze the changes in the temporal and spatial distribution of the Beijing urban heat island intensity (UHII) and the impact of mass human migration on urban temperature. Soil moisture, 10-m wind speed, and cloud cover were considered and indicated nearly no change during the pre-CNY period (2 to 4 weeks before CNY) and CNY week, which means that UHII variation was mainly affected by the mass human migration. Daily UHII during CNY week was lower than during pre-CNY period. UHII for daily maximum temperature decreased by 55% during CNY week than the pre-CNY period (0.6 &#176;C during pre-CNY period vs. 0.27 &#176;C during CNY week) due to mass human migration, which was much larger than the reduction in UHII for the daily maximum temperature (5%, 4.34 &#176;C during the pre-CNY period vs. 4.11 &#176;C during the CNY week). The spatial distribution of the UHII difference between CNY week and the pre-CNY period is closely related to the locations of functional population zones. UHII for daily maximum temperature decreases most (80%, 0.40 &#176;C during the pre-CNY period vs. 0.08 &#176;C during the CNY period) between the Third and Fourth Ring Roads (RRs), an area which experiences high human activity and has the highest floating population percentage. This study can provide suggestions for optimizing the layout of urban space and land-use structures.</p>

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The Impact of the Urban Heat Island during an Intense Heat Wave in Oklahoma City

Advances in Meteorology ◽

10.1155/2010/230365 ◽

2010 ◽

Vol 2010 ◽

pp. 1-10 ◽

Cited By ~ 78

Author(s):

Jeffrey B. Basara ◽

Heather G. Basara ◽

Bradley G. Illston ◽

Kenneth C. Crawford

Keyword(s):

Urban Heat Island ◽

Heat Wave ◽

Rural Areas ◽

Oklahoma City ◽

Apparent Temperature ◽

Heat Island ◽

Atmospheric Conditions ◽

Urban Heat ◽

The Impact ◽

Intense Heat

During late July and early August 2008, an intense heat wave occurred in Oklahoma City. To quantify the impact of the urban heat island (UHI) in Oklahoma City on observed and apparent temperature conditions during the heat wave event, this study used observations from 46 locations in and around Oklahoma City. The methodology utilized composite values of atmospheric conditions for three primary categories defined by population and general land use: rural, suburban, and urban. The results of the analyses demonstrated that a consistent UHI existed during the study period whereby the composite temperature values within the urban core were approximately C warmer during the day than the rural areas and over C warmer at night. Further, when the warmer temperatures were combined with ambient humidity conditions, the composite values consistently revealed even warmer heat-related variables within the urban environment as compared with the rural zone.

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Observational evidence of urban heat island intensification during heatwaves in European cities

10.5194/egusphere-egu21-12369 ◽

2021 ◽

Author(s):

Marco Possega ◽

Leonardo Aragão ◽

Paolo Ruggieri ◽

Marco Antonio Santo ◽

Silvana Di Sabatino

Keyword(s):

Urban Heat Island ◽

Rural Areas ◽

Observational Evidence ◽

Extreme Heat ◽

Mitigation Strategies ◽

Maximum Temperature ◽

Daily Maximum ◽

Heat Island ◽

European Cities ◽

Urban Heat

<p>Heatwaves (HWs) are extreme weather conditions characterized by persistent high temperatures with considerable impacts on society in terms of mortality, thermal stress and energy demand of the population. One of the most interesting aspects of HWs concerns the interaction with the phenomenon of urban heat island (UHI). The UHI is the tendency of urbanized areas to have warmer temperatures than the surrounding rural areas, mainly due to the thermal properties of materials forming urban environment and the heat produced by human activities. Some studies analyzed the behavior of UHI during periods of extreme heat, showing an amplification of the gradient of temperature between urban and rural areas in HW conditions, but the results are often limited to case studies with a single HW and/or a specific city. Other papers dealt with the same topic by examining events on various cities using outputs of global models, but with resolution insufficient to include in detail urban-scale processes and therefore to take into account specific properties of the cities investigated. The approach of this work consisted in providing observational evidence and extending the aforementioned results, studying the effect of HWs on UHI in about ten European cities with different characteristics (geography, topography, urban planning) through the analysis of daily maximum/minimum temperatures data measured by meteorological stations for the summers of period 2006-2019. In particular, the intensity of UHI was assessed through the computation of a Composite UHI Index (UHII), defined as the difference between averaged urban and non-urban values. The different behavior of UHII during HWs compared to "normal" summer days (NO) in selected European cities was investigated, detecting an intensification of index values regarding periods of extreme heat for the majority of examined locations. More specifically, the analysis of temporal evolution of UHII was conducted, revealing an average increase of this index during the occurrence of HW events. Moreover, a correlation between UHI index and maximum temperature anomalies was examined, and HW days appeared to exhibit a larger percentage of positive UHII with respect to NO days, showing also higher absolute values. This work provides an indication of how European urban areas respond to severe hot periods and could be useful to validate numerical model simulations for more detailed analysis, for example regarding mitigation strategies. Finally, the emergence of some outliers, namely cities whose UHI manifested a different reaction to HWs, may deserve dedicated studies in the future.</p>

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Review on Urban Heat Island in China: Methods, Its Impact on Buildings Energy Demand and Mitigation Strategies

Sustainability ◽

10.3390/su13020762 ◽

2021 ◽

Vol 13 (2) ◽

pp. 762

Author(s):

Liu Tian ◽

Yongcai Li ◽

Jun Lu ◽

Jue Wang

Keyword(s):

Energy Consumption ◽

Urban Heat Island ◽

Building Energy ◽

Design Stage ◽

Heat Island ◽

Building Energy Consumption ◽

Rapid Urbanization ◽

Substantial Impact ◽

Urban Heat ◽

The Impact

High population density, dense high-rise buildings, and impervious pavements increase the vulnerability of cities, which aggravate the urban climate environment characterized by the urban heat island (UHI) effect. Cities in China provide unique information on the UHI phenomenon because they have experienced rapid urbanization and dramatic economic development, which have had a great influence on the climate in recent decades. This paper provides a review of recent research on the methods and impacts of UHI on building energy consumption, and the practical techniques that can be used to mitigate the adverse effects of UHI in China. The impact of UHI on building energy consumption depends largely on the local microclimate, the urban area features where the building is located, and the type and characteristics of the building. In the urban areas dominated by air conditioning, UHI could result in an approximately 10–16% increase in cooling energy consumption. Besides, the potential negative effects of UHI can be prevented from China in many ways, such as urban greening, cool material, water bodies, urban ventilation, etc. These strategies could have a substantial impact on the overall urban thermal environment if they can be used in the project design stage of urban planning and implemented on a large scale. Therefore, this study is useful to deepen the understanding of the physical mechanisms of UHI and provide practical approaches to fight the UHI for the urban planners, public health officials, and city decision-makers in China.

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Social media reveal ecoregional variation in how weather influences visitor behavior in U.S. National Park Service units

Scientific Reports ◽

10.1038/s41598-021-82145-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Emily J. Wilkins ◽

Peter D. Howe ◽

Jordan W. Smith

Keyword(s):

National Park ◽

National Park Service ◽

Spatial Behavior ◽

Maximum Temperature ◽

Daily Maximum Temperature ◽

Daily Maximum ◽

Daily Weather ◽

Visitor Behavior ◽

Park Service ◽

The Impact

AbstractDaily weather affects total visitation to parks and protected areas, as well as visitors’ experiences. However, it is unknown if and how visitors change their spatial behavior within a park due to daily weather conditions. We investigated the impact of daily maximum temperature and precipitation on summer visitation patterns within 110 U.S. National Park Service units. We connected 489,061 geotagged Flickr photos to daily weather, as well as visitors’ elevation and distance to amenities (i.e., roads, waterbodies, parking areas, and buildings). We compared visitor behavior on cold, average, and hot days, and on days with precipitation compared to days without precipitation, across fourteen ecoregions within the continental U.S. Our results suggest daily weather impacts where visitors go within parks, and the effect of weather differs substantially by ecoregion. In most ecoregions, visitors stayed closer to infrastructure on rainy days. Temperature also affects visitors’ spatial behavior within parks, but there was not a consistent trend across ecoregions. Importantly, parks in some ecoregions contain more microclimates than others, which may allow visitors to adapt to unfavorable conditions. These findings suggest visitors’ spatial behavior in parks may change in the future due to the increasing frequency of hot summer days.

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Climate-informed decision-making for urban design: Assessing the impact of urban morphology on urban heat island

Urban Climate ◽

10.1016/j.uclim.2021.100776 ◽

2021 ◽

Vol 36 ◽

pp. 100776

Author(s):

Luis G.R. Santos ◽

Ido Nevat ◽

Gloria Pignatta ◽

Leslie K. Norford

Keyword(s):

Decision Making ◽

Urban Heat Island ◽

Urban Design ◽

Urban Morphology ◽

Informed Decision ◽

Informed Decision Making ◽

Heat Island ◽

Urban Heat ◽

The Impact

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Characterization of the subsurface urban heat island and its sources in the Milan city area, Italy

Hydrogeology Journal ◽

10.1007/s10040-021-02387-z ◽

2021 ◽

Author(s):

Alberto Previati ◽

Giovanni B. Crosta

Keyword(s):

Urban Heat Island ◽

Urban Areas ◽

Heat Fluxes ◽

Shallow Aquifer ◽

Heat Island ◽

Groundwater Temperature ◽

City Area ◽

Groundwater Environment ◽

Urban Heat ◽

The Impact

AbstractUrban areas are major contributors to the alteration of the local atmospheric and groundwater environment. The impact of such changes on the groundwater thermal regime is documented worldwide by elevated groundwater temperature in city centers with respect to the surrounding rural areas. This study investigates the subsurface urban heat island (SUHI) in the aquifers beneath the Milan city area in northern Italy, and assesses the natural and anthropogenic controls on groundwater temperatures within the urban area by analyzing groundwater head and temperature records acquired in the 2016–2020 period. This analysis demonstrates the occurrence of a SUHI with up to 3 °C intensity and reveals a correlation between the density of building/subsurface infrastructures and the mean annual groundwater temperature. Vertical heat fluxes to the aquifer are strongly related to the depth of the groundwater and the density of surface structures and infrastructures. The heat accumulation in the subsurface is reflected by a constant groundwater warming trend between +0.1 and + 0.4 °C/year that leads to a gain of 25 MJ/m2 of thermal energy per year in the shallow aquifer inside the SUHI area. Future monitoring of groundwater temperatures, combined with numerical modeling of coupled groundwater flow and heat transport, will be essential to reveal what this trend is controlled by and to make predictions on the lateral and vertical extent of the groundwater SUHI in the study area.

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