Aerodynamic roughness variation with vegetation: analysis in a suburban neighbourhood and a city park.

ABSTRACT

Local aerodynamic roughness parameters (zero-plane displacement, z d , and aerodynamic roughness length, z 0 ) are determined for an urban park and a suburban neighbourhood with a new morphometric parameterisation that includes vegetation. Inter-seasonal analysis at the urban park demonstrates z d determined with two anemometric methods is responsive to vegetation state and is 1-4 m greater during leaf-on periods. The seasonal change and directional variability in the magnitude of z d is reproduced by the morphometric methods, which also indicate z 0 can be more than halved during leaf-on periods. In the suburban neighbourhood during leaf-on, the anemometric and morphometric methods have similar directional variability for both z d and z 0 . Wind speeds at approximately 3 times the average roughness-element height are estimated most accurately when using a morphometric method which considers roughness-element height variability. Inclusion of vegetation in the morphometric parameterisation improves wind-speed estimation in all cases. Results indicate that the influence of both vegetation and roughness-element height variability are important for accurate determination of local aerodynamic parameters and the associated wind-speed estimates.