Abstract
Urban areas have well-documented effects on climate, such as the urban
heat island (UHI) effect, reduction of wind speeds, enhanced turbulence
and boundary layer heights, and changes in cloud cover and
precipitation. The aim of this study is to quantify the impact of the
urban area of London on local and regional climate. This is achieved
through the coupling of the non-hydrostatic mesoscale model METRAS with
the sophisticated urban canopy scheme BEP. The model is configured for
case studies of the London region, for typical UHI conditions, and the
model results are evaluated using data from meteorological monitoring
sites. This study develops a methodology to quantify the regional impact
of urbanisation from numerical model results. The urban area, in its
current form, is found to affect near surface temperature, the diurnal
temperature range, the UHI, and the near surface wind speed and
direction. For the selected cases, peak UHI intensities of up to 2.5 K
are found during night time hours, with the timing and magnitude of the
peak showing good agreement with previous experimental studies for
London. The timing of the UHI peak intensity for the current urban land
cover for London shows a good agreement with the results of
measurements. A significant reduction in wind speed over the urban area
was also simulated during both daytime and night time, due to the higher
roughness of the city compared to the rural domain. The effect is shown
to have a regional character, with both urban and surrounding rural
areas demonstrating a significant impact. Thus, the UHI can not only be
understood when focussing on local data, but the interaction with the
surrounding needs to be considered.
