The Edinburgh Academy

Investigation into the urban microclimate of Edinburgh

James Anderson (extracts)

Introduction to the whole project

The population of the UK is expected to rise by two million by 2010. The demand for housing produced as a result of this increase puts pressure upon existing urban areas and many new homes must be created to accommodate the increased growth.  Urban areas are therefore likely to expand and many new towns must be created. The expansion of urban areas brings great worry to many conservationists, who feel that air pollution, water pollution and urban waste are to increase and become more of a problem.  At present man's modem living is altering the rural environment significantly, and this effect is likely to worsen as the population increases. However it is not only the environment that will be affected.  Suprisingly the local climate could also be altered.  Tall regularly spaced buildings, reduced areas of open space, and a higher influence of concrete could all alter the natural 'rural' albedo of the area, affecting such aspects as temperature and humidity.  The aim of this investigation is to study the urban microclimate of Edinburgh, and to analyse the difference between urban and rural locations. Why the city of Edinburgh?  Presently Edinburgh is experiencing rapid urban change, as demand for housing and commerce within the city is so great.  Derelict brownfield sites are being developed, and the city is expanding further and further into the urban fringe, eating up greenbelt land.  As a result of this development, I feel there is no better location to study the effects of urbanisation on the climate, as the rural/urban differences will start becoming more apparent and important as the city grows.

Extract from the orientation of buildings experiment

Study Questions: Analysis Of Building Orientation Data

As is seen in the data display some temperature readings were taken in the sun, and others in the shade, depending upon which side of the street the results were taken from.  A problem therefore existed of which results to include.  Should the readings in the sun be included, although the standard temperature reading method forbids it and it was proven from an identical position that readings in the shade and sun were separated by a 2.5 C difference? If these warm readings are to be included then another problem becomes apparent - there are a different number of warm readings on each transect (6 for the transect running N/S, but only 4 for the transect running E/W).  If this data is averaged then surely the higher number of warm temperatures would reflect greatly upon the final result, making the reading inaccurate and the experiment unfair. It was decided to ignore the warm temperatures, as a result of the above problems, and base the analysis upon the readings taken in the shade.

If the readings from the more shaded sections of the transects are averaged (see results table) a very startling difference is noticeable.  There is a 0.7 C difference in temperature between the N/S running transect and the E/W running transect , with the warmer transect suprisingly being the one running N/S (7.9 C for Northumberland Street - EIW, 8.6 C for Dundas Street - N/S). The proposed model was thus proven incorrect. 

Why was this so?

1. The low sun angle in the sky:

As the possible relationship was only stumbled upon whilst analysing the results for the urban temperature transects, the data gathering had to be undertaken during the winter months.  Thus the sun remained at a low angle in the sky, with resultant rays barely passing over the roofs of opposite houses.  Thus, when the results for this section were gathered, the sun had not entered much of the urban canyon due to this blocking effect and never reached pavement level, except through gaps in the housing layout.  This would have lowered temperatures somewhat. Indeed, this poor penetration into the canyons, would have reduced temperatures in a number of ways.  Reflection of radiation would have been reduced as the S" was not covering such a substantial amount of the building surface area thus, the amount of energy absorbed by these reflections would have been reduced resulting in lower temperatures. The reduced surface area available for absorption would have reduced the amount of insulation absorbed causing temperatures to drop, also. The North/South running Dundas streets was not affected by this low sun angle, as the incident solar rays did not have to pass over any buildings.  Thus the street was bathed in sunshine, at least in part throughout the day, which would have increased temperatures somewhat (no insulation was blocked out).  The buildings of the two streets would have still received the same intensity of insulation, as the streets were located in the same local proximity.

2. The activity and land

Dundas street (N/S) with its commercialised nature attracts far more traffic and pedestrians than the quieter and more withdrawn Northumberland street (E/W).  Dundas street is also a significant transport route linking the CBD with more suburban areas (Cannonmills/ Trinity), whereas Northumberland Street, although a connecting road, does not.  Thus, the amount of traffic on these roads is likely to differ substantially, affecting the amount of heat absorbed by these buildings, as motor vehicles radiate large amounts of heat energy.  These varying amounts of heat energy released to the different streets did not make the experiment fair, as it is unknown whether the orientation of the buildings, or the varying activity along these streets which accounted for the difference in temperatures.

Final Conclusion