Key Conclusions of the First International Urban Land Surface Model Comparison Project

Abstract

The First International Urban Land Surface Model Comparison was designed to identify three aspects of the urban surface–atmosphere interactions: 1) the dominant physical processes, 2) the level of complexity required to model these, and 3) the parameter requirements for such a model. Offline simulations from 32 land surface schemes, with varying complexity, contributed to the comparison. Model results were analyzed within a framework of physical classifications and over four stages. The results show that the following are important urban processes: i) multiple reflections of shortwave radiation within street canyons; ii) reduction in the amount of visible sky from within the canyon, which impacts the net longwave radiation; iii) the contrast in surface temperatures between building roofs and street canyons; and iv) evaporation from vegetation. Models that use an appropriate bulk albedo based on multiple solar reflections, represent building roof surfaces separately from street canyons and include a representation of vegetation demonstrate more skill, but require parameter information on the albedo, height of the buildings relative to the width of the streets (height to width ratio), the fraction of building roofs compared to street canyons from a plan view (plan area fraction), and the fraction of the surface that is vegetated. These results, while based on a single site and less than 18 months of data, have implications for the future design of urban land surface models, the data that need to be measured in urban observational campaigns, and what needs to be included in initiatives for regional and global parameter databases.

Modeling the Partitioning of Turbulent Fluxes at Urban Sites with Varying Vegetation Cover

“…However, a sensitivity study shows that 519 an amount of 0.035 mm each hour gives a modelled median of β that is close to that observed (Fig. The initial soil moisture conditions have been shown previously to be critical for modelling sensible 582 and latent heat fluxes in urban environments (Best and Grimmond, 2015a). Hence it requires only a small amount of water to be added each hour to explain the observed β, 521 so it is possible that such a source of water is responsible for the observed evaporation.…”

“…Typically these models are designed to 47 represent the energy balance of the various facets that make up an idealized urban canopy. Indeed, the first 57 international urban model comparison experiment (PILPS-Urban) concluded that for the two urban 58 sites considered in the study (Vancouver and Melbourne), models that included a representation of 59 vegetation performed much better in simulating the sensible (QH) and latent heat (QE) densities than 60 models that neglected it (Grimmond et al, 2010, 2011, Best and Grimmond, 2013, 2015a. Whilst this may be a good 52 representation of the central downtown areas of major cities, this design alone (i.e., without a 53 representation of vegetation) does not capture the influence of vegetation present in many street 54 canyons and abundant in the suburbs of many cities.…”

“…Indeed, the first 57 international urban model comparison experiment (PILPS-Urban) concluded that for the two urban 58 sites considered in the study (Vancouver and Melbourne), models that included a representation of 59 vegetation performed much better in simulating the sensible (QH) and latent heat (QE) densities than 60 models that neglected it (Grimmond et al, 2010, 2011, Best and Grimmond, 2013, 2015a. Indeed, the first 57 international urban model comparison experiment (PILPS-Urban) concluded that for the two urban 58 sites considered in the study (Vancouver and Melbourne), models that included a representation of 59 vegetation performed much better in simulating the sensible (QH) and latent heat (QE) densities than 60 models that neglected it (Grimmond et al, 2010, 2011, Best and Grimmond, 2013, 2015a.…”

A comprehensive assessment of land surface-atmosphere interactions in a WRF/Urban modeling system for Indianapolis, IN

“…Loridan et al, 2013;Bohnenstengel et al, 2011;Kondo et al, 2005;Masson et al, 2000) that aimed to more accurately represent the complex processes that occur in these environments. The inaccuracies have been well documented (Best and Grimmond, 2015) and there have been studies done that have utilized parameterization techniques and different model schemes to try and get better agreement between the model and the observations (e.g. Loridan and Grimmond, 2012;Loridan et al, 2010).…”

Different Patterns in Daytime and Nighttime Thermal Effects of Urbanization in Beijing-Tianjin-Hebei Urban Agglomeration

“…It is possibly because nighttime SUHI mainly resulted from the higher thermal admittance of building materials in urban areas than rural areas, which does not change significantly across seasons [29]. Another key factor affecting nighttime SUHII is anthropogenic heat emissions [67,68] from appliances, transportation systems and infrastructures, factories and other human activities, which exist all year around.…”