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.

中文翻译：

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地表风速背风防风林水平分布的半经验模型

利用防风林是一种全球普遍的农业生产管理实践，通过减少风引起的破坏来恢复退化的生态系统。检查防风林如何影响背风面风速对于量化防风林的效率至关重要。结合风洞实验和流行文献，开发了一种用于模拟背风式防风林风速水平分布的半经验模型。模型模拟了带加速和减速项的水平背风风速分布防风林；同时考虑四个关键影响因素（防风空气动力学孔隙率、表面粗糙度、理查森数和风入射角）。它还包括一种简单的定量方法，用于从光学孔隙率确定防风林的空气动力学孔隙率。模型结果与已发表数据的比较表明，该模型在不同防风结构和湍流条件下的各种风速分布中具有鲁棒性。模拟结果表明水平风速分布肯定取决于防风林的孔隙度。风速随着风入射角的增加而下降。当水平距离为防风林高度的2～20倍时，风速随着理查森数的增加而明显降低，随着表面粗糙度的降低而略有降低。而且，不断增大的风入射角加强了防风孔隙度对风速的弱化作用，同时减少理查森数会随着表面粗糙度的增加而扩大相对风速的减少区间。该模型提供了一种简单实用的方法来更好地评估防风林的影响，可以将其纳入农业决策决策中，以减少风的不利影响。