Forest and urban climate meteorology

The dynamics of fire growth is strongly influenced by the kinematics of flow through porous vegetation and urban structures (the canopy). The local wind and turbulence environment at the source determines the initial spread of a fire. Wind profiles vary depending upon the density (porosity) of the surrounding objects, their distribution vertically or laterally, the presence of below canopy open regions, and the distance 

Once a hot smoke plume rises above the underlying canopy the buoyant force of a large fire leads to significant plume rise. The plume rise trajectory and the dispersion of its materials can be predicted. The effect of small-scale atmospheric turbulence, initial plume cross-sectional aspect ratio is minimal on plume trajectory, but the magnitude of atmospheric turbulence, atmospheric stratification, and ground terrain on rate of dispersion can be significant [363, 634], 

The superposition of individual tree wakes results in the under-forest and aboveforest velocity features found in extensive areas of forests or woods. The initial growth of wake deficits and the subsequent decay at greater downwind distances are characteristics of both individual tree and forest measurements. Yano [663] developed a concept of momentum defect superposition in the wakes of an array of roughness elements to reproduce velocity, turbulence and shear distributions within and above canopies. 

Different profiles have been proposed using first order closure models which specify a simple eddy diffusivity, K, and a drag coefficient, Cd, to describe that portion of the mean wind profile which exists beneath the forest ceiling for constant foliage distribution  

The atmospheric boundary layer (ABL) is that portion of the atmosphere where surface drag due to the motion of the air relative to the ground modifies synoptic-scale motions caused by horizontal pressure gradients, Coriolis forces, and buoyancy. The depth of the ABL is highly variable (50 to 2000 m), but it generally increases with proximity to the equator, with wind speed, and as the earth surface roughness, but it decreases 

---

The theory reviewed and discussed here has already found a number of practical applications, particularly in the meteorology of forests and complex topography, Chapter 5, the hydraulics of open water flows, Chapter 6, the thermal performance of spraying coolers, Chapters 1 and 3 and the mitigation of large fire danger, Chapter 8 as well as in urban air pollution, emergency preparedness and prediction of urban climate, Chapter 9. 

---