Simulating surface–plant–air interactions inside urban environments with a three dimensional numerical model

In recent years high-resolution numerical simulation of surface–plant–air interactions as an important part of global circulation models (GCM) or as a tool to assist in planning decisions has experienced increased consideration. In contrast large scale phenomena described in GCMs, the lower part of the atmosphere where we live is very sensitive to small scale processes which can develop an individual local climate, different to the expected average conditions. Especially in urban areas the great variety of different surfaces and sheltering obstacles produces a pattern of distinct microclimate systems. To simulate these local effects, microscale surface–plant–air interaction schemes with a special extension to typical artificial urban boundaries are needed. The paper focuses on the microscale numerical simulation of surface–plant–air interactions inside urban structures, especially the feedback between artificial surfaces like buildings and vegetation inside street canyons, backyards or greens. The three-dimensional non-hydrostatic model ENVI-met is presented and used to solve the basic equations forward in time and can simulate ‘hardʹ wind field modifications (solid boundaries) like walls as well as ‘softʹ modifications (porous shelters) like vegetation. A case study of building a small park inside the CBD area will show what effects even small changes can have on local flow and temperature fields.