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UBC Theses and Dissertations

Verification of urban energy balance models Loudon, Sheila Margaret


Three urban energy balance models have been tested against data gathered in a suburb of Vancouver, British Columbia. The major incentive behind this study was that these models had not previously been verified in urban areas, due mainly to the lack of appropriate data. As the available models represent a range of complexity, and utilize a variety of different methods, it was thought to be worthwhile to test all three. Input for the models consists of temporal and spatial information, meteorological data, and site surface characteristics. Values for the former two sets of inputs were relatively easy to come by. Values for the surface characteristics, however, were quite difficult to determine with any degree of confidence, due to the complexity of the suburban surface. This was particularly discouraging because it was found that the models were very sensitive to the values chosen for these inputs. The sensitivity analyses also showed that the simplest model (Myrup, 1969), of the three, sometimes exhibited rather unrealistic responses to variations in the input parameters. The other two models (Ackerman, 1977; Carlson and Boland, 1978) usually showed more reasonable responses. Eighteen days, from the available data set, were chosen for testing the models. The modelled values were compared to those observed using comparative statistics, scatter diagrams, and time series plots. It was found that the errors in the modelled net all-wave radiation were quite small, and were due mainly to errors in the modelling of the net long-wave radiaton. The modelled surface heat fluxes, on the other hand, were in poor agreement with those observed. This was attributed to the methods used for representing surface moisture. The errors in the mixed layer heights, as produced by the two more complex models, were also high. Unfortunately, the modelled surface temperatures could not be quantitatively assessed due to the lack of appropriate measurements. However, those of the simple model seemed to be unrealistic, whereas those of the other two models seemed reasonable. It was concluded that without some improvements, particularly in surface moisture representation, the models would have little practical value.

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