基于数学期望的风向和风速对农田防护林网防风效能的影响

Influence of Wind Direction and Speed on the Windbreak Efficiency of Farmland Shelterbelt Networks Based on Mathematical Expectation

为研究农田防护林网在全年的时间尺度上对不同方向有害风的综合防护效能,在野外实地观测不同风向(与主林带夹角分别为90.0°,67.5°,45.0°,22.5°和0°)和风速(5.2和7.3m/s)条件下的林网内防风效能,根据各风向有害风发生频率计算数学期望值,利用克里金(Kriging)插值法进行模拟,并用地统计学的方法分析防护林网的空间自相关性.结果表明:防护林对不同风向的风均有较强的防护作用,随着风向与主林带夹角的减小,平均风速呈现出增大的趋势,防风效能分别达到69.5%,66.2%,60.4%,59.8%和50.1%;不同风速条件下防风效能均达到50%以上,低风速和高风速时平均有效防护面积分别为90.1%和44.0%;不同风速条件下林网内空间变异系数分别与指数模型和高斯模型相拟合,林带内风速块金值较低,变程较大,具有强烈的空间自相关性和样本区间的合理性.

In order to study the comprehensive protective benefits of farmland shelterbelt networks against harmful winds in different directions throughout a year,different wind directions（the angles to the main forest belt were 90.0°,67.5°,45.0°,22.5°,and 0°,respectively）and speeds（5.2 and 7.3 m/s）were observed in the field.The mathematical expectation values were calculated according to the occurrence frequency of the wind at each wind direction,simulated by Kriging interpolation,and the spatial autocorrelation of shelterbelt networks was analyzed using geostatistics.The results showed as following：1）Shelterbelt had a strong protective effect under winds of different directions.With a decrease in the angle between the wind direction and the main forest belt,the mean wind speed showed an increasing trend,and the windbreak efficiency reached 69.5%,66.2%,60.4%,59.8% and 50.1%,respectively.2）Windbreak efficiency under different speeds can reach more than 50%.The average effective protection area under low wind speed can reach 90.1%,while under high wind speed it is 44.0%.3）The spatial variability coefficients of the shelterbelt under different wind speed conditions can be fitted with an exponential model and a Gaussian model.The shelterbelt nugget of the wind was lower,its range was larger,and it had a strong spatial autocorrelation and rationality of the sample interval.