Evidence of horizontal urban heat advection in London using six years of data from a citizen weather station network

Abstract

Recent advances in citizen weather station (CWS) networks, with data accessible via crowd-sourcing, provide relevant climatic information to urban scientists and decision makers. In particular, CWS can provide long-term measurements of urban heat and valuable information on spatio-temporal heterogeneity related to horizontal heat advection. In this study, we make the first compilation of a quasi-climatologic dataset covering 6 years (2015–2020) of hourly near-surface air temperature measurements obtained via 1560 suitable CWS in a domain covering south-east England and Greater London. We investigated the spatio-temporal distribution of urban heat and the influences of local environments on climate, captured by CWS through the scope of Local Climate Zones (LCZ) – a land-use land-cover classification specifically designed for urban climate studies. We further calculate, for the first time, the amount of advected heat captured by CWS located in Greater London and the wider south east England region. We find that London is on average warmer by about 1.0 °C to 1.5 °C than the rest of south-east England. Characteristics of the southern coastal climate are also captured in the analysis. We find that on average, urban heat advection (UHA) contributes to 0.22±0.96 °C of the total urban heat in Greater London. Certain areas, mostly in the centre of London are deprived of urban heat through advection since heat is transferred more to downwind suburban areas. UHA can positively contribute to urban heat by up to 1.57 °C, on average and negatively by down to -1.21 °C. Our results also show an important degree of inter- and intra-LCZ variability in UHA, calling for more research in the future. Nevertheless, we already find that UHA can impact green areas and reduce their cooling benefit. Such outcomes show the added value of CWS when considering future urban design.

Urban heat in Johannesburg and Ekurhuleni, South Africa: A meter-scale assessment and vulnerability analysis

“…It is noted that the warmer air temperatures also persist up to several kilometers downwind the city bounds. This phenomenon, urban heat advection, is also observed in other recent modeling and observational studies ( Cosgrove and Berkelhammer, 2018 , Brousse et al, 2022 , Dinda and Chatterjee, 2022 ).

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Unequal distributions of crowdsourced weather data in England and Wales

“…Natural areas tend to have a lower proportion of their total area covered by a PWS with ∼0.03 PWS per km 2 on average; no PWS are present in LCZ E. Built-up LCZs, which compose only 11 362 km 2 of England and Wales (7.5 % of the total 151 139 km 2 ), hence concentrate most of the PWS. The latter confirms that PWS could be regarded as a valuable palliation to the characteristic climate data scarcity in urban areas 5,27 .…”

“…We collect data on PWS only for those active during the recent summer 2022 (June to August) as this was a record-breaking year in daily max temperature in England and Wales with temperatures going as high as 40.3 • C 50 . This also ensures that a maximum of PWS are included in the analysis since their number has kept increasing over the past decade 5 .…”

“…Over recent decades, the number of weather devices operated by independent individuals who openly share the data collected as a crowdsourcing activity 4 has rapidly increased in European countries, including the United Kingdom 5 . We refer to these devices as personal weather stations (PWS) to contrast them with official automatic weather stations installed by meteorological offices.…”

High resolution heat stress over a Sahelian city: Present and future impact assessment and urban green effectiveness

“…Most methods use thermal land surface temperature measurements derived from satellite data to map urban environments and their surroundings which, in turn, can be used to derive urban heat stress (Mallick et al, 2013; Rodrigues de Almeida et al, 2021; Zhou et al, 2019). Other studies such as Meier et al (2017) and Brousse et al (2022) use a collection of atmospheric data retrieved from citizen weather stations. However, each approach has its disadvantages.…”