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Centre (LWC) were used in order to select cases representing both extreme heat events and typical summer conditions. Since one of the aims of this chapter was to analyse the London urban heat island, some simulations (the 6 th -7 th August 1998 and 30 th -31 st July 1999 cases) were performed for periods for which a strong heat island was present and had been referenced in the literature (Best 2005; GLA 2006). For the purposes of selecting the simulations, the heat island was analysed by comparing the central London temperatures from the LWC station with those at the Larkhill station, which is situated sufficiently far from urban land use London so as not to be affected by the city (see Figure 3.6 on page 84). Surface data from this location was also used in the initialization process, together with radiosonde profiles from the UK stations closest to London (Larkhill and Herstmonceux). 138
Table 5.2: Selected periods of simulation for the evaluation of METRAS+BEP Simulation period Description / Weather conditions 28 th -30 th June 1995 18 th -20 th August 1995 15 th -16 th August 1997 6 th -7 th August 1998 30 th -31 st July 1999 Non directional anti cyclonic weather type. Low cloud. High average night time temperatures. Non directional anti cyclonic weather type. Low cloud. High average night time temperatures. Anti cyclonic weather type (0/5). High average night time temperatures. Strong UHI. Part of an extended period of strong UHI, clear skies and low winds. Weather type 16/6. Light easterly winds, predominantly clear sky night time conditions. Hotter than average temperatures. Anti cyclonic weather type ¾. 19 th -21 st July 2000 Low/few clouds. Non directional anti cyclonic weather type (0). 24 th -25 th August 2000 5.1.1 Urban parameters Low cloud. Non directional anti cyclonic weather type (0). The methods used to set up the model for the city of London are described in Chapter 3. The urban land use was taken from the CEH Land Cover Map 2000, and the building morphology and thermal parameters characterising the urban area were also described in Chapter 3. 139
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MODELLING THE IMPACT OF URBANISATIO
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Abstract Urban areas have well docu
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Abbreviations aLMo Meteo Swiss oper
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4.2.2 Impact of the urban area on t
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List of figures Figure 2.1: Scales
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Figure 4.21: Diurnal variation of t
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Figure 6.16: Mean horizontal wind s
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Chapter 1: Introduction Urban areas
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with trends derived from a statisti
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scheme, and therefore it was necess
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The effects of future urban expansi
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2.1 Urban climate modification Urba
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latitudes (Taha 1997), and this is
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100 - 200 m 1 - 2 km 10 - 20 km 100
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epresentatively sample the underlyi
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over the city centre, convergent fl
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Cold islands can also occur in urba
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of the atmosphere. For example, it
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amount of solar radiation absorbed
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(Peterson 1969; Changnon 1992; Coll
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2.3 Justification of modelling appr
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Trusilova (2006) carried out a stud
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constant flux surface layer in the
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the vertical distribution of vegeta
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using different building parameters
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Table 2.2: SWOT analysis for the ME
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Fraction of urban land cover [%] Fi
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The built up area of London can cur
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Figure 2.5(a-f): Builtup area of Lo
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• Mainly high density development
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climate of London, and currently on
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For mid-latitude cities, of which L
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warming of 0.04 °C per decade, in
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out differences in the urban heat i
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adopted in previous studies ranges
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y the implementation of a specific
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A prognostic equation is used to re
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At the surface the temperature is c
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The boundary conditions used for th
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are defined in the file m1tini_TAPE
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The terms representing the impact o
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3.2.1 Calculation of dynamical effe
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θ k ∆z / 2 H Siu (Equation 3.12)
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3.3 Implementation of BEP in METRAS
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difficulties in the linking of the
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Table 3.3: Description of how the 2
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3.5.2 Orography data Orography data
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epresenting suburban development a
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Table 3.7 shows a summary of the MI
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3.6 Summary In this PhD study the m
Page 101 and 102: temperature, air pressure and air d
Page 103 and 104: Potential temperature [K] Figure 4.
Page 105 and 106: Wind speed [ms -1 ] Figure 4.2: Ver
Page 107 and 108: 4.2.1 Horizontal cross sections of
Page 109 and 110: affected, as the flow bends around
Page 111 and 112: Downwind of the city on the other h
Page 113 and 114: the city, which is expected since t
Page 115 and 116: Potential temperature [K] Figure 4.
Page 117 and 118: simulation this effect is verticall
Page 119 and 120: differences are expected during day
Page 121 and 122: tend to cool the surface, but can a
Page 123 and 124: Figure 4.15 shows the vertical prof
Page 125 and 126: appropriate value for these paramet
Page 127 and 128: 0.61) and that of conventional grav
Page 129 and 130: Difference in potential temperature
Page 131 and 132: educed near surface temperatures of
Page 133 and 134: fraction was increased in steps of
Page 135 and 136: works. In the control simulation th
Page 137 and 138: characterised by the albedo, therma
Page 139 and 140: is higher by a similar amount. The
Page 141 and 142: (a) Potential temperature [K] (c) T
Page 143 and 144: Figure 4.25 shows the vertical sect
Page 145 and 146: tests also reproduced well document
Page 147 and 148: Chapter 5: Evaluation of the urbani
Page 149 and 150: Fraction of urban land cover [%] Fi
Page 151: For the summers of 1995-2000 the an
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Page 157 and 158: newly urbanised version of the METR
Page 159 and 160: adiation trapping in the street can
Page 161 and 162: the second day of simulation (31 st
Page 163 and 164: Air temperature ( o C) 35 30 25 20
Page 165 and 166: the model. The smaller percentage o
Page 167 and 168: Wind speed (ms -1 ) Wind direction
Page 169 and 170: London Heathrow Airport (LHR) Wind
Page 171 and 172: A full set of hourly wind speed and
Page 173 and 174: contain both roofs exposed to direc
Page 175 and 176: Chapter 6: The effects of urban lan
Page 177 and 178: simulations with two hypothetical s
Page 179 and 180: dependent on the r(i,j), the radial
Page 181 and 182: centre of the domain was more than
Page 183 and 184: 6.2 Effects of the current state of
Page 185 and 186: During daytime the shape of the are
Page 187 and 188: The calculation was performed for t
Page 189 and 190: ecause finding a rural reference po
Page 191 and 192: development (GLA 2006) and differen
Page 193 and 194: 6.2.4 Wind speed and direction Klai
Page 195 and 196: Wind speed and direction (ms -1 ) F
Page 197 and 198: “urban” cells to be affected by
Page 199 and 200: the urban surface. Many other studi
Page 201 and 202: eason the near surface potential te
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Mean potential temperature at 12:00
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where A(x) is the area affected by
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Table 6.8: REI for the RADIUS, DENS
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COMBINED series also show a reducti
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for all runs in the series, and cor
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The runs are then combined into one
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to be more linear than the smaller
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The total reduction in mean wind sp
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The REI showed that for all the var
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Higher temperatures in the urban ar
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Over the next ten years the populat
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7.1.1 EXPANSION series The first sc
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Another cause of this form of expan
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7.2 Effects of urbanisation for the
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Mean near surface potential tempera
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UHI intensity (K) 4 3.5 3 2.5 2 1.5
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temperature, an increase in the mea
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7.2.3 Wind speed The effect of the
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7.3 Effects of urbanisation for the
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mean near surface potential tempera
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7.3.2 Wind speed Changes in the mea
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expansion strategies such as the re
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should also be considered to avoid
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models, for example Martilli et al.
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cities (Baker et al. 2002). Already
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uses, painting the roofs white to r
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The full influence of different met
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References Abercrombie, P. (1945).
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Bottema, M. (1997). "Urban Roughnes
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Craig, K. J. and R. D. Bornstein (2
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Grimmond, C. S. B. and T. R. Oke (2
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Jin, M. and J. M. Shepherd (2005).
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Lemonsu, A. and V. Masson (2002). "
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Nitis, T., Z. B. Klaic and N. Mouss
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alance in urban areas - Recent adva
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Seaman, N. L. (2000). "Meteorologic
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Therry, G. and P. Lacarrere (1983).
Page 277:
Yague, C., E. Zurita and A. Martine
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