Mass human migration and Beijing’s urban heat island during the Chinese New Year holiday

Zhang, Jingyong; Wu, Lingyun; Yuan, Fei; Dou, Jingjing; Miao, Shiguang

doi:10.1007/s11434-015-0809-9

Cited by 33 publications

(26 citation statements)

References 6 publications

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“…These changes affect the surface energy balance (SEB) and the boundary layer structure, resulting in well‐known urban climate effects, such as the urban heat island, degradation of air quality and enhanced heat waves and flooding (UN‐Habitat, ). Thus, it is critical to understand the exchanges of heat, mass, and momentum between the atmosphere and the urban surface to inform urban development and design (Grimmond et al, ) and to evaluate strategies to mitigate inadvertent effects, such as heat stress (Zhang et al, ). This is particularly important in megacities in China where data on these SEB exchanges, the development of parameterizations, and the evaluation and application of numerical models are still all limited.…”

Section: Introductionmentioning

confidence: 99%

Summertime surface energy balance fluxes at two Beijing sites

Dou

Grimmond

Zou

et al. 2019

Intl Journal of Climatology

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Summertime (June–August 2015) radiative and turbulent heat fluxes were measured concurrently at two sites (urban and suburban) in Beijing. The urban site has slightly lower incoming and outgoing shortwave radiation, lower atmospheric transmissivity and a lower surface albedo than the suburban site. Both sites receive similar incoming longwave radiation. Although the suburban site had larger daytime outgoing longwave radiation (L↑), differences in the daily mean L↑ values are small, as the urban site has higher nocturnal L↑. Overall, both the midday and daily mean net all‐wave radiation (Q*) for the two sites are nearly equal. However, there are significant differences between the sites in the surface energy partitioning. The urban site has smaller turbulent sensible heat (Q H) (21–25% of Q* [midday–daily]) and latent heat (Q E) fluxes (21–45% of Q*). Whereas, the suburban proportions of Q* are Q H 32–32% and Q E 39–66%. The daily (midday) mean Bowen ratio (Q H/Q E) was 0.56 and 0.49 (0.98 and 0.83) for the urban and suburban sites, respectively. These values are low compared with other urban and suburban areas with similar or larger fractions of vegetated cover. Likely, these are caused by the widespread external water use for road cleaning/wetting, greenbelts, and air conditioners. Our suburban site has quite different land cover to most previous suburban studies as crop irrigation supplements rainfall. These results are important in enhancing our understanding of surface–atmosphere energy exchanges in Chinese cities and can aid the development and evaluation of urban climate models and inform urban planning strategies in the context of rapid global urbanization and climate change.

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Section: Introductionmentioning

confidence: 99%

Summertime surface energy balance fluxes at two Beijing sites

Dou

Grimmond

Zou

et al. 2019

Intl Journal of Climatology

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“…The UHII tmax during the CNY week decreased notably, with the higher average UHII tmax 0.60 °C occurring in the pre‐CNY period and lower average UHII tmax 0.27 °C in CNY week, which is consistent with Zhang et al . (). A similar phenomenon is observed in UHII tave , but the decrease rate is much smaller than UHII tmax (14% vs 55%), with lower UHII during CNY week than during the pre‐CNY period (2.12 vs 2.48 °C) (Figure (b)).…”

Section: Resultsmentioning

confidence: 97%

“…Zhang et al . () found that Beijing UHII is affected by migration based on 20 automatic weather stations (AWSs) in Beijing from 2004 to 2013.…”

Section: Introductionmentioning

confidence: 99%

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

Dou

Miao

2017

Intl Journal of Climatology

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The Chinese New Year (CNY, also called Spring Festival), which officially lasts for 7 days, is the most important festival 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'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 data during CNY 2010–2015 were used to analyze the changes in temporal and spatial distribution of 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 (2–4 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 °C during pre‐CNY period versus 0.27 °C during CNY week) due to mass human migration, which was much larger than the relative reduction in UHII for the daily minimum temperature (5%, 4.34 °C during the pre‐CNY period versus 4.11 °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 °C during the pre‐CNY period versus 0.08 °C during the CNY period) between the Third and Fourth Ring Roads (RRs), an area which experiences high frequency human activities and has high floating population percentage. This study can provide suggestions for optimizing the layout of urban space and land‐use structures.

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“…Indeed, recent studies demonstrated that the massive population outflows can have the cooling effects on urban temperature212223. It was evident that UHI effect of Beijing averaged over 2009–2013 declined by 0.64 °C during the CNY holiday week relative to the nearby non-holiday period as the anthropogenic heat release decreased substantially21. However, this research is based on the analysis to two urban stations and two non-urban reference stations for a short period.…”

mentioning

confidence: 95%

“…The massive population outflows from large cities during the CNY holiday can largely reduce anthropogenic heat release and also alter some other processes, and may thus exert noticeable impacts on urban climate. Indeed, recent studies demonstrated that the massive population outflows can have the cooling effects on urban temperature212223. It was evident that UHI effect of Beijing averaged over 2009–2013 declined by 0.64 °C during the CNY holiday week relative to the nearby non-holiday period as the anthropogenic heat release decreased substantially21.…”

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confidence: 99%

Influence of human population movements on urban climate of Beijing during the Chinese New Year holiday

Zhang

2017

Sci Rep

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The population movements for the Chinese New Year (CNY) celebrations, known as the world’s largest yearly migration of human beings, have grown rapidly in the past several decades. The massive population outflows from urban areas largely reduce anthropogenic heat release and modify some other processes, and may thus have noticeable impacts on urban climate of large cities in China. Here, we use Beijing as an example to present observational evidence for such impacts over the period of 1990–2014. Our results show a significant cooling trend of up to 0.55 °C per decade, particularly at the nighttime during the CNY holiday relative to the background period. The average nighttime cooling effect during 2005–2014 reaches 0.94 °C relative to the 1990s, significant at the 99% confidence level. The further analysis supports that the cooling during the CNY holiday is attributable primarily to the population outflow of Beijing. These findings illustrate the importance of population movements in influencing urban climate despite certain limitations. As the world is becoming more mobile and increasingly urban, more efforts are called for to understand the role of human mobility at various spatial and temporal scales.

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Mass human migration and Beijing’s urban heat island during the Chinese New Year holiday

Cited by 33 publications

References 6 publications

Summertime surface energy balance fluxes at two Beijing sites

Summertime surface energy balance fluxes at two Beijing sites

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

Influence of human population movements on urban climate of Beijing during the Chinese New Year holiday

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