Evolution and Performance of the Urban Scheme in the Unified Model Aurore Porson, Ian Harman, Pete Clark, Martin Best, Stephen Belcher University of Reading JCMM- Met Office

History of the Urban Tile  No urbanization apart from manual increase in roughness over London.  1996 Tile scheme in SSFM (SCM + relaxation forcing from operational 12 km UK Mes) with urban tile.  1998 Operational SSFM with urban canopy tile.  2000 Operational 12 km Mesoscale model with urban canopy tile  2004 Surface-only model research implementation of two-tile model with modified surface parameters  2004 SCM research implementation of two-tile model depending on canyon geometry  April 2005 Operational 4 km with urban canopy tile.  March 2006 Operational 4 km adds change to anthropogenic heat source.  April D model research implementation of two-tile model depending on canyon geometry

Blending Height Surface UM Tile Surface Exchange  Treats heterogeneous surfaces using ‘blending height’ techniques.  Nine surface types, –Broad Leaf Trees –Needle Leaf Trees –C3 Grass –C4 Grass –Shrub –Urban –Water –Soil –Ice  Each tile has a full surface energy balance.  4 layer soil temperature and moisture. Schematic of potential temperature profile at nighttimes

 s  T s 4  g  T g 4 H E  s  T s 4 G RNRN The Urban Canopy Model – M. Best  This includes a radiatively coupled ‘canopy’: – high thermal inertia to simulate wall effects, – weak coupling with the soil, – strong coupling with the atmosphere.  The urban tile also has: –Enhanced roughness. –Enhanced drainage. –Modified albedo.

Formation of the night time urban heat island – urban canopy tile Unified Model – 1 km resolution 76 Layers Point 2 Point 3 Point 1 Point 4 Point 1: Upstream Point 2: Central London Point 3: Downstream Suburbs Point 4: Downstream Rural Urban fraction is derived from 25 m resolution data, based LANDSAT and generated by CEH Temperature (K) Height above ground (m)

Operational Implementation  WMO Block 3 stations  London  5 cities index

Impact of the Urban Canopy in Met Office Operational Mesoscale Model BIAS RMS ERROR MONTHLY TEMPERATURE ERRORS

Impact of Anthropogenic Heat Fluxes – P. Clark LONDON ALTNAHARRA MONTHLY TEMPERATURE ERRORS From statistics on full energy consumption over the UK from 1995 through to 2003 Monthly heat flux values vary from 17 W/m2 (August) to 26 W/m 2 (December) Data averaged over 21 cases, representative of ‘typical’ weather conditions

Surface-only tests against Mexico City and Vancouver data show that the model performance increases if:  The ratio between roughness length for heat and momentum is reduced.  The urban tile is split into one canyon and one roof. Development of a two-tile model with reduced roughness length for heat roughness length for heat Sensible Heat Flux for Mexico City (Best, Grimmond and Villani, 2006)

(Best, Grimmond and Villani, 2006)

Improvement of two-tile model: dependence on canyon geometry  Averaging over Canyon Orientations Identical Walls Identical Walls  One Surface Energy Balance for the Canyon (Mixing, Exchange of Radiation) and One for the Roof Identical Walls and Street Identical Walls and Street  Geometry Effects on: –Radiation: Effective Albedo and Emissivity –Transfer of Heat: Surface Resistance Network –Increase in Thermal Inertia The new two-tile model = Simplification of a four-tile model

Improvement of the two-tile model: Radiation Albedo and Emissivity to depend on canyon geometry and to include exchange of radiation in the canyon (I. Harman, 2004) to include exchange of radiation in the canyon (I. Harman, 2004)

T roof T wall1 T wall2 T street From a 4-tile model towards a 2-tile model The way the canyon transfers scalars differs significantly from a flat surface (J. Barlow et al., 2004, I. Harman et al., 2004) The way the canyon transfers scalars differs significantly from a flat surface (J. Barlow et al., 2004, I. Harman et al., 2004) Improvement of the Two-Tile Model: Geometry Dependent Transfer Coefficients T roof T canyon

r1r1 r2r2 Formulation of Total Resistance Formulation of Facet Resistance Formulation of Heat Roughness Length U(  ) U(1)

Improvement of the two-tile model: Storage of Heat Surface heat flux to the soil G is defined as: Independent testing showed that this technique is more efficient than multiplying the heat capacity W W HH

Independent set of comparison: 4-tile and 2-tile models 4-tile and 2-tile models Surface Energy Balance Difference in Heat Flux for H/W =0.1, 0.5, 1., 1.5, 2, 3 Both models are forced with averaging over canyon orientations for solar radiation and equal surface parameters in the canyon H/W=0.1 H/W=3 Validation through idealized simulations

Independent set of comparison: 4-tile and 2-tile models 4-tile and 2-tile models Validation against Mexico City observations Observations 4-tile 2-tile

Future Work  TESTS: –Full comparison between the urban canopy and the canyon geometry dependent two-tile model –Further improvement of the resistance network to include recirculation and ventilated areas  Implementation of drag bulk approach  3D CASE STUDIES: –Mapping canyon geometry for urban land use. Creation of new ancillaries –One-year simulation over London  PERSPECTVES –Design of building scenarios for adaptation to climate change

Thank you for your attention !

Anthropogenic Heat  Energy Consumption for UK in million of tonnes of oil equivalent  Conversion to W / m 2 for urban areas, being ~ 2.9 % UK area  70 % is assumed to be produced in urban areas (the rest being for net inputs conversion and lost in generation)  Out of the 70 %, estimates of energy dissipation per sector: –28.5 % domestic with 80% of dissipation –32.5 % transport with 67% of dissipation –20.5% industry with 75% dissipation –18.5 % with 50 % dissipation, –giving 69.2% of dissipation  Anthropogenic Heat = Conversion Factor to W / m 2 * 70%*69.2%

Physical Parametrizations  Edwards-Slingo Radiation –(Edwards & Slingo 1996)  Mixed phase precipitation –(Wilson & Ballard 1999) –Extending to prognostic cloud fraction (Wilson, Bushell) –Extending to prognostic cloud water, rain water, ice, snow, graupel (Forbes)  Met Office Surface Exchange Scheme (MOSES I and II) –(Cox, Essery, Betts)  Non-local Boundary Layer –(Lock et al 2000)  New GWD scheme + GLOBE orography, smoothed (Raymond filter)  Mass flux convection scheme with CAPE closure, downdraft and momentum transport, separate shallow cumulus –(Gregory and Rowntree, Kershaw, Grant)

Canyon and Roof Tiles – M. Best

Effect of Thermal Capacity – M. Best

Formation of the night time urban heat island – urban canopy tile Urban-No-Urban near surface temperature difference Unified Model – 1 km resolution 76 Layers