The urban heat island (UHI) is a well-known effect of urbanisation and is particularly important in world megacities. Overheating in such cities is expected to be exacerbated in the future as a result of further urban growth and climate change. Demonstrating and quantifying the impact of individual design interventions on the UHI is currently difficult using available software tools. The tools developed in the LUCID ('The Development of a Local Urban Climate Model and its Application to the Intelligent Design of Cities') research project will enable the related impacts to be better understood, quantified and addressed. This article summarises the relevant literature and reports on the ongoing work of the project. Practical applications: There is a complex relationship between built form, urban processes, local temperature, comfort, energy use and health. The UHI effect is significant and there is a growing recognition of this issue. Developers and planners are seeking advice on design decisions at a variety of scales based on scientifically robust, quantitative methods. The LUCID project has thus developed a series of tools that (1) quantify the effect of urbanisation processes on local environmental conditions, and (2) quantify the impact of such conditions on comfort, energy use and health. The use of such tools is vital, both to inform policy but also to be able to demonstrate compliance with it.

Abstract. A coupled regional-to-local modelling system comprising a regional chemistry-climate model with 5 km horizontal resolution (EMEP4UK) and an urban dispersion and chemistry model with explicit road source emissions (ADMS-Urban) has been used to simulate air quality in 2012 across London. The study makes use of emission factors for NO x and NO 2 and non-exhaust emission rates of PM 10 and PM 2.5 which have been adjusted compared to standard factors to reflect real-world emissions, with increases in total emissions of around 30 % for these species. The performance of the coupled model and each of the two component models is assessed against measurements from background and near-road sites in London using a range of metrics concerning annual averages, high hourly average concentrations and diurnal cycles. The regional model shows good performance compared to measurements for background sites for these metrics, but under-predicts concentrations of all pollutants except O 3 at near-road sites due to the low resolution of input emissions and calculations. The coupled model shows good performance at both background and near-road sites, which is broadly comparable with that of the urban model that uses measured concentrations as regional background, except for PM 2.5 where the under-prediction of the regional model causes the coupled model to also under-predict concentrations. Using the coupled model, it is estimated that 13 % of the area of London exceeded the EU limit value of 40 µg m −3 for annual average NO 2 in 2012, whilst areas of exceedances of the annual average limit values of 40 and 25 µg m −3 for PM 10 and PM 2.5 respectively were negligible.

By comparison with both experimental and numerical data, Dysthe's (1979) O(ε4) modified nonlinear Schrödinger; equation has been shown to model the evolution of a slowly varying wavetrain well (here ε is the wave steepness). In this work, we extend the equation to include a prescribed, large-scale, O(ε2) surface current which varies about a mean value. As an introduction, a heuristic derivation of the O(ε3) current-modified equation, used by Bakhanov et al. (1996), is given, before a more formal approach is used to derive the O(ε4) equation. Numerical solutions of the new equations are compared in one horizontal dimension with those from a fully nonlinear solver for velocity potential in the specific case of a sinusoidal surface current, such as may be due to an underlying internal wave. The comparisons are encouraging, especially for the O(ε4) equation.

No abstract

ADMS-Urban, an advanced three dimensional, quasi-Gaussian model nested within a simple trajectory model, has been used to model urban air quality in many cities across the world, calculating street scale resolution of concentration over city-scale domains. It has been used for all the purposes described under the EU Air Quality Directive, namely: assessment of compliance with air quality limit values; planning and mitigation; source apportionment; short term forecasting. In assessing compliance with the PM10 air quality limit values, cities including London are increasingly looking into pollution hotspots where local effect such as street canyons and the street geometry are important. There is also increasing awareness of the importance of modelling spatial variations in the urban background and the influence of changes in meteorology on the urban scale on this background. Since its initial development ADMS-Urban has modelled the local (street scale) impact of two-sided, symmetrical street canyons on dispersion within the canyon using a model based on OSPM (Operational Street Pollution Model) (Kakosimos et al, 2011). It has allowed for the impact on dispersion immediately downwind of a street of noise barriers on one or on both sides of a street. It has considered NOx chemistry (NO, NO2, O3, VOC) and generation of sulphate using a local chemistry model and also a grid-based trajectory model to account for the chemical reactions on the city-scale. This paper describes ongoing developments that extend the application of ADMS-Urban at both city and the local scale. At the city scale ADMS-Urban has been developed to use gridded meteorological and chemistry output from regional models (with grid scale down to 1km). This nesting of ADMS-Urban within a regional-scale numerical model allows seamless modelling from regional through to the local (street) scale. At the street scale ADMS-Urban is being extended to model explicitly a number of local effects including single-sided and asymmetrical street canyons, streets on embankments, streets in cuttings, elevated roads (flyovers) and tunnel exits.