黄河上游宁夏-内蒙古段跃移沙粒起动风速的空间分布

摘要

Through the Hedong Sandy Land, the Ulanbuh Desert, and the Kubuqi Desert, Ningxia-Inner Mongolia Reach of the Yellow River suffered from serious blown sand hazard. A mass of aeolian sediment deposited in the Yellow River and brought a serious siltation in the Yellow River. It is in urgent need to develop a warning system to reveal the spatial distribution of threshold wind velocity for wind erosion in the watershed of the Ningxia-Inner Mongolia Reach of the Yellow River. The aim of this research is to provide theoretical guidance to prevent the blown sand hazard in this region. In this research, integrated Normalized Difference Vegetation Index (NDVI) data set and the observations in the study area, the threshold wind velocities of different surfaces were calculated, and spatial distribution of threshold wind velocity for wind erosion in the study area was revealed. Firstly, using a map of NDVI, we calculated the vegetation coverage, frontal area, and roughness length in the study area. Then, the frontal area was used to calculate the threshold friction velocity by the vegetation influence function. With tested calculation method of threshold friction velocity using the observed sand flux data, we found the simulated errors were all small. Based on the truth that the wind profiles above the study area all obeyed logarithmical functions, we estimated the spatial distribution of threshold wind velocity for wind erosion in the watershed of Ningxia-Inner Mongolia Reach of the Yellow River. We found that most of the regions that with wind erosion risk were near the Yellow River. At last, this paper proposed a method that using the maximum NDVI in this year to predict the threshold wind velocity based on the relationship between NDIV in the next windy season and maximum that in this year. We hope this research would provide some theoretical advises for predicting the wind erosion hazard in the watershed of the Ningxia-Inner Mongolia Reach of the Yellow River.%　　黄河上游宁夏-内蒙古段穿越河东沙地、乌兰布和沙漠和库布奇沙漠，大量风沙被吹入黄河，因此，迫切需要揭示宁夏-内蒙古河段沙粒起动风速的空间分布规律，从而为该区域的风沙防治工作提供理论依据。首先，应用归一化植被指数（normalized different vegetation index，NDVI）数据集计算该河段地表植被盖度、植被迎风面积指数与粗糙度。而后，通过植被迎风面积指数计算摩阻起动风速的影响函数，研究河段摩阻起动风速的空间分布。利用实测数据检验摩阻起动风速的计算方法，表明摩阻起动风速的计算方法误差较小。研究表明，研究区内风速廓线均呈对数函数的分布规律，并利用风速廓线方程计算了研究区不同下垫面（10 m高度）处的起动风速，进而得到跃移沙粒起动风速的空间分布。结果显示研究区风蚀风险最大的几个区域大多临近黄河。最后，根据当年最大NDVI值与下一年风季（3月至5月）NDVI平均值之间的关系，提出利用当年最大NDVI值对下一年风季起动风速的预测方法，该研究为黄河宁夏-内蒙古段的风蚀预报提供理论支撑。