Abstract/Summary

The surface aerodynamic roughness parameters of the zero-plane displacement (zd) and roughness length (z0) can be critical for wind-speed estimates in the atmospheric boundary layer. In urban areas, the numerous sources and sinks of momentum makes it challenging to assign appropriate values for zd and z0. The objective of this PhD is to improve the understanding of zd and z0 in urban environments, especially for wind-speed estimates when flow is free from roughness-element wakes. Nine methods are applied to determine zd and z0 at three sites in central London (UK), demonstrating the inter-method variability leads to a wide range of values. Wind-speed estimates using the roughness parameters and five wind-speed profile methods are compared to Doppler lidar observations up to 200 m (approximately 10 times the average building height) above the canopy. Estimates with roughness parameters determined from morphometric methods (i.e. based upon surface geometry) which directly incorporate roughness-element height variability are consistently most accurate. A morphometric method is developed to calculate zd and z0 that accounts for both buildings and vegetation. The method captures the directional and seasonal variability of roughness with vegetation and improves the accuracy of wind-speed estimates. Due to the challenge of obtaining urban morphology and roughness parameters for cities globally, three satellite-derived global digital elevation models (GDEMs) are assessed using benchmark elevation datasets. It is concluded that empirical corrections to the most accurate GDEM (TanDEM-X) can improve the parameter accuracy and associated wind-speed estimates.