A semiempirical model for horizontal distribution of surface wind speed leeward windbreaks

The utilization of windbreaks is a globally prevailing management practice for agricultural production and restoration of degraded ecosystems by reducing wind-induced destruction. Examining how windbreaks affect leeward surface wind speed is critically important to quantify the efficiency of windbreaks. A semiempirical model for simulating horizontal distribution of wind speed leeward windbreaks was developed, combining wind tunnel experiments with prevailing literature. The model simulated the horizontal leeward wind speed distribution windbreaks with acceleration and deceleration terms; simultaneously considering four key impact factors (windbreak aerodynamic porosity, surface roughness, Richardson number and wind incident angle). It also comprises of a simple quantitative method for determining windbreak aerodynamic porosity from optical porosity. Model results compared with published data illustrate that the model is robust in various wind speed distributions under different windbreak structures and turbulence conditions. The simulation results indicate horizontal wind speed distribution is definitely dependent upon windbreak porosity. Wind speeds decline with increasing wind incident angle. Wind speeds decrease obviously with increasing Richardson number while decrease slightly with decreasing surface roughness, when the horizontal distance is between two and twenty times the windbreak height. Moreover, the escalating wind incident angle strengthens the weakening effects of windbreak porosity on wind speed, while reducing Richardson numbers expand the decreasing intervals of relative wind speed with increasing surface roughness. The model provides a simple and practical method to better assess the impacts of windbreaks, which can be incorporated in agricultural policy-making decisions to reduce the detrimental impacts of wind.