Simulations of the London urban heat island

Abstract

We present simulations of London's meteorology using the Met Office Unified Model with a new, sophisticated surface energy-balance scheme to represent the urban surfaces, called MORUSES. Simulations are performed with the urban surfaces represented and with the urban surfaces replaced with grass in order to calculate the urban increment on the local meteorology. The local urban effects were moderated to some extent by the passage of an onshore flow that propagated up the Thames estuary and across the city, cooling London slightly in the afternoon. Validations of screen-level temperature show encouraging agreement to within 1-2 K, when the urban increment is up to 5 K. The model results are then used to examine factors shaping the spatial and temporal structure of London's atmospheric boundary layer. The simulations reconcile the differences in the temporal evolution of the urban heat island (UHI) shown in various studies and demonstrate that the variation of UHI with time depends strongly on the urban fetch. The UHI at a location downwind of the city centre shows a decrease in UHI during the night, while the UHI at the city centre stays constant. Finally, the UHI at a location upwind of the city centre increases continuously. The magnitude of the UHI by the time of the evening transition increases with urban fetch. The urban increments are largest at night, when the boundary layer is shallow. The boundary layer experiences continued warming after sunset, as the heat from the urban fabric is released, and a weakly convective boundary layer develops across the city. The urban land-use fraction is the dominant control on the spatial structure in the sensible heat flux and the resulting urban increment, although even the weak advection present in this case study is sufficient to advect the peak temperature increments downwind of the most built-up areas.

The Effects of Heat Advection on UK Weather and Climate Observations in the Vicinity of Small Urbanized Areas

“…Klysik and Fortuniak 1999;Bohnenstengel et al 2011;Azevedo et al 2016), they do not explicitly separate urban heat advection from the UHI signal (i.e. (i) the locally generated UHI component with intensity dependent upon underlying land use, and (ii) the urban heat advection that is generated from upwind urban land use).…”

Rooftop Surface Temperature Analysis in an Urban Residential Environment

“…The UHI exacerbates heat waves during the summer, increases energy consumption, and more importantly elevates the risk of heat-related morbidity and mortality, especially for the elderly, young children, and low-income residents, who are more vulnerable to excessive heat stress due to a variety of physical, social, and economic reasons [5][6][7][8][9]. Many existing studies have made attempts to understand and mitigate UHI effect in major cities all over the world, such as London, Beijing, Paris, Shanghai, Hong Kong, and Moscow [10][11][12][13][14][15][16]. UHI mitigation via sustainable design of the urban environment has received increasing attention from ecologists, urban planners, and policymakers.…”

The impact of the London Olympic Parkland on the urban heat island

“…Further, sources of anthropogenic heat emission, for example, vehicles, buildings and industry, add to the heat emission and affect the overall heat balance (Taha 1997;Ichinose, Shimodozono, and Hanaki 1999;Offerle, Grimmond, and Fortuniak 2005;Hamilton et al 2009;Sailor 2010) and have been shown to increase the temperature due to the UHI, i.e. the UHI increment (UHII) by 1-2 • C (Ichinose, Shimodozono, and Hanaki 1999;Bohnenstengel et al 2011). This source of additional energy release is added as a positive value to the surface energy balance.…”

“…London's UHI is well described (for example, Howard 1818; Watkins et al 2002;Kolokotroni and Giridharan 2008;Bohnenstengel et al 2011;Mavrogianni et al 2011), and the nocturnal summertime UHII has been shown to be approximately 2 • C (Kolokotroni and Giridharan 2008). During periods of extreme weather, for example, the 2003 heat wave, parts of central London were up to 10 • C warmer than the surrounding rural zone (GLA 2010).…”