Gerald Mills

Progress toward sustainable settlements: a role for urban climatology

SummarySustainable development can be defined as that which meets the needs of the current generation while leaving sufficient resources for the needs of future generations. A central objective is to decouple conventional resource use (and its corollary, waste generation) from economic development through technological innovation, improved efficiency and changes in individual practices. As the global population becomes urbanized and human activity is concentrated in urban areas, settlement planning is a key aspect of sustainability. The widespread inclusion of environmental objectives in urban plans at all scales provides an opportunity for the incorporation of urban climate knowledge into the planning process on a routine basis. Many of the stated objectives have both direct and indirect connections to climate. However, for this to happen, climate research and results must be linked more explicitly to the objectives of the sustainable settlement. In this paper, the relevance of sustainability to urban design and climate is discussed and the potential contribution of current urban climatology is assessed, identifying areas of special consideration for transfer to achieve sustainable urban planning and design.

An urban canopy-layer climate model

SummaryThis paper outlines a computer simulation model designed to assess the thermal characteristics of the urban canopy layer (UCL). In contrast to other UCL models, the layer simulated here includes both closed volumes (buildings) and open volumes (canyons). The purpose of the model is to allow the comparison of the climate impacts of different building group configurations. Traditional boundary-layer theory is applied to the surface urban boundary layer (UBL) which lies above the UCL and the derived relations are used to parameterize exchanges of momentum and heat across the UBL/UCL interface. The exterior energy budgets of the roof, walls and floor of the canopy are solved using an equilibrium surface temperature method. The open canopy and interior building air temperatures are found which are in agreement with the surface exchanges. Using measured data for Los Angeles in June, the output of the model is examined. The results show some agreement with measurement studies and suggest that the density of structures can have a substantial impact on UCL/UBL interaction.

Simulation of the energy budget of an urban canyon-I. Model structure and sensitivity test

Abstract This paper presents the formulation and results of a simple numerical model designed to simulate the climate of an urban canyon. The model is two-dimensional in nature and is based on the observation that ambient airflow which tranverses the long-axis of a symmetrical canyon drives a circulating vortex within the canyon air space which results in the exchange of heat, mass and momentum at the canyon top. A simple model is described which consists of two components: a semi-empirical model to relate within-canyon airflow to ambient wind velocity, and an energy budget model for canyon surfaces. The model is capable of simulating many aspects of the canyon climate, including the canyon surface and top energy budget and surface and air temperatures. Sensitivity tests with the model indicate that the canyon top energy budget is remarkably stable for many changes in canyon parameters. Canyon geometry (expressed as a height/width ratio) caused the greatest changes with increased narrowness being associated with less heat exchange across the canyon top. The models predictions appear intuitively reasonable and compare well with existing measurement data. The results suggest that the coupling between the urban boundary and canopy layers in terms of heat exchange may be a function of canyon geometry.

Modelling the water budget of Ireland—evapotranspiration and soil moisture

The water budget is one of the must important exchange cycles within the earthatmosphere system. When applied to a surface it accounts for the partition of precipitation into evapotranspiration. runoff and ehanges in soil-water storage. While there has been work published on some of these components, few have attempted to evaluate these within the context of the water budget. In this paper a simple model is applied to a 5x5km grid superimposed on the land area ol Ireland. The model uses measured monthly values of meteorological variables (precipitation, temperature and sunshine hours) and databases of landuse and elevation to calculate each of the water budget terms. The results for the thirty-year period 1961–1990 are presented and seem to conform to the known climate of the period.

The radiative effects of building groups on single structures

Abstract The role of building group configuration in controlling the heating and cooling abilities of structures is considered. A computer model is described which simulates the thermal stresses of simple building groups composed of identical structures. The natural heating of the structures is measured as a function of the daily exposure of individual structures to direct sunlight. The cooling of structures is measured as a function of their sky view factor. Building groups are compared in terms of these measures at different latitudes and times of the year. The results show that group design can have a significant impact on the thermal stresses experienced by individual buildings.

Urban Surface Energy Balance Models: Model Characteristics and Methodology for a Comparison Study

Many urban surface energy balance models now exist. These vary in complexity from simple schemes that represent the city as a concrete slab, to those which incorporate detailed representations of momentum and energy fluxes distributed within the atmospheric boundary layer. While many of these schemes have been evaluated against observations, with some models even compared with the same data sets, such evaluations have not been undertaken in a controlled manner to enable direct comparison. For other types of climate model, for instance the Project for Intercomparison of Land-Surface Parameterization Schemes (PILPS) experiments (Henderson-Sellers et al., 1993), such controlled comparisons have been shown to provide important insights into both the mechanics of the models and the physics of the real world. This paper describes the progress that has been made to date on a systematic and controlled comparison of urban surface schemes. The models to be considered, and their key attributes, are described, along with the methodology to be used for the evaluation.

Classification of Local Climate Zones Using SAR and Multispectral Data in an Arid Environment

There is an urgent need for more detailed spatial information on cities globally that has been acquired using a standard method to facilitate comparison and the transfer of scientific and practical knowledge between places. As part of the world urban database and access portal tools (WUDAPT) initiative, a simple workflow has been developed to perform this task. Using freely available satellite imagery (Landsat) and software (SAGA), WUDAPT characterizes settlements using the local climate zone (LCZ) scheme, which decomposes the city into distinctive neighborhoods (>1 km2) based on typical properties (e.g., green proportion and built fraction). In this paper, the methodology is extended to examine the effect of adding synthetic aperture radar (SAR) data, which is now freely available from Sentinel 1, for generating LCZs. Using the city of Khartoum as a case study, the results show that combining multispectral and SAR data improves the overall performance of several classifiers, with random forest (RF) performing the best overall.

Simulation of the energy budget of an urban canyon—II. Comparison of model results with measurements

Abstract A simple numerical model that attempts to simulate the energy budget of an urban canyon is assessed by comparing its predictions against measurements made at an urban field site. A street is chosen that satisfieds many of the models requirements and a measurement scheme is devised to measure variables which are also simulated. The model is run using input information collected from the field and the data produced are compared with the measured data. The results indicate that the model is capable of simulating many of the climate attributes (such as surface temperatures and net radiation at the canyon top) accurately, but does not simulate the dominant mechanism of sensible heat exchange between the canyon and its environment. Nevertheless, the model predicts a small and largely invariant exchange, similar to that measured. The results of the field study, when compared with other published work, indicates that as street canyons become narrower they become increasingly isolated in terms of heat exchange from the overlying atmosphere. The results of the computer runs appear to follow this pattern.

Developing a community-based worldwide urban morphology and materials database (WUDAPT) using remote sensing and crowdsourcing for improved urban climate modelling

This paper outlines the WUDAPT (World Urban Database and Access Portal Tools) concept and highlights progress to date in developing this database for cities around the world. The next steps in the WUDAPT project are outlined, both in the immediate and longer term. Ultimately the goal is to provide an open access resource on urban morphology, materials and metabolism for all major cities that can be used for many different applications, in particular for climate and weather modelling, and urban climate change studies.

BUILDING DENSITY AND INTERIOR BUILDING TEMPERATURES: A PHYSICAL MODELING EXPERIMENT

The effect of building density on the interior temperatures of buildings is explored using scaled physical models. The urban canopy layer is modeled as a single-cube structure surrounded by a wall that represents neighboring structures. Each physical model was constructed of plywood and consisted of a cube 200 mm in height, enclosed by a wall 200 mm in height. Four models were constructed corresponding to height/width ratios (H/W) of 4, 2, 1, and 0.5 and placed at an exposed site located at 34°N. The interior air temperature of each cube, direct and diffuse solar radiation on a horizontal surface, and ambient air temperature and wind velocity were measured over a period from late November 1996 to early June 1997. To extract the influence of building density, air temperatures were compared against those measured in the model representing a H/W of 1. The results show that nighttime cooling is primarily a function of building density, but that daytime heating depends on the interaction of density with changi...