1.中国科学院西北生态环境资源研究院 干旱区生态安全与可持续发展重点实验室/敦煌戈壁荒漠生态与环境研究站,甘肃 兰州 730000
2.中国科学院大学,北京 100049
3.甘肃省水土保持科学研究所,甘肃 兰州 730020
作者简介 About authors
基于土壤风蚀预报系统(WEPS)算法,结合多源地理数据,计算了河西走廊-塔克拉玛干沙漠边缘阻击战核心区2000—2023年土壤风蚀及PM10范围,分析其时空变化特征及主要影响因素。结果表明:在研究区总面积80.67万km²内,多年平均风蚀模数为3 553 t·km-2,风蚀高值区集中在塔克拉玛干沙漠东南缘及河西走廊中部。总体上,由于研究区风速下降、植被覆盖度和降水量增加,风蚀模数呈下降趋势,年代下降速率为41 t·km-2,减少区域占总面积的48%。同期,PM10的多年平均释放量为3.11×107 t,平均释放速率为38.53 t·km-2·a-1。在各季节中,春季风蚀模数最高,占年内风蚀总量的47%。风速、植被覆盖度和土壤湿度是关键影响因素,风速对风蚀的贡献率超过90%。
关键词:河西走廊-塔克拉玛干沙漠边缘;土壤风蚀;PM10;WEPS
This study utilizes the Wind Erosion Prediction System (WEPS) algorithm, combined with multi-source geographical data, to calculate soil wind erosion and PM10 in the core area of the battle against desertification along the Hexi Corridor-Taklimakan Desert edge since 2000. It analyzes the spatiotemporal variation characteristics and primary influencing factors. The results indicate that within the total study area of 806 700 km², the multi-year average wind erosion modulus is 3 553 t·km-2, with high wind erosion concentrations observed in the southeastern margin of the Taklamakan Desert and the central Hexi Corridor. Overall, due to decreasing wind speeds, increasing vegetation cover, and increased precipitation in the study area, the wind erosion modulus exhibits a downward trend, with an average decrease rate of 41 t·km-2 per decade, and the area experiencing reduction accounts for 48% of the total. Meanwhile, the annual average PM10 emission is 3.11×107 t, with an average annual rate of 38.53 t·km-2. Among the seasons, spring exhibits the highest wind erosion modulus, accounting for 47% of the annual total. Correlation analysis reveals that wind speed, vegetation cover, and soil moisture are key influencing factors, with wind speed contributing over 90% to wind erosion.
Keywords:Hexi Corridor-Taklimakan Desert edge;soil wind erosion;PM10;WEPS
本文引用格式
本研究采用土壤风蚀预报系统WEPS的核心算法,使用气象、土壤和植被等多源地理数据分析了2000—2023年河西走廊-塔克拉玛干沙漠边缘阻击战核心区的风蚀量及PM10变化趋势,探讨其主要影响因素,以期深化对该研究区风沙活动及其影响的认识,为“三北”重点生态建设工程布局与优化、提升防风固沙生态系统服务功能提供科学依据和决策参考。
图1研究区概况
注:根据国家地理信息公共服务平台(天地图)服务网站审图号为GS(2024)0650号的标准地图制作,底图边界无修改
Fig.1Overview of study area
Table 1 Data sources
本研究采用WEPS中的风蚀测算方案,结合气象、土壤质地、植被特征等数据,使用ArcGIS10.2在研究区内建立5 km×5 km格网,在小时级的时间步长内分别计算每个栅格的风蚀和PM10总量,并叠加各栅格结果,根据区域面积给出整体风蚀模数和PM10释放速率。基本方程如下:
当地表有直立植被时,需计算直立植被对摩阻风速的降低作用,因此观测地点摩阻风速由气象站摩阻风速u*f和有无植被摩阻风速u* 共同计算得到:
式中:u*f为气象站摩阻风速,m·s-1;u为高度为z时风速;z为观测风速的高度(通常情况获取的标准观测风速的高度是10 m);z0f为空气动力学粗糙度,取25 mm;z0为当地空气动力学粗糙度,取地表垄作粗糙度与随机粗糙度的最大值;u*b为观测地点无植被时的摩阻风速,m·s-1。
观测地点有植被覆盖的摩阻风速u* 依据有效生物量拖曳系数大小,采用下列公式来进行计算。
式中:u*v为植被冠层上部摩阻风速,m·s-1;WZov为直立植被冠层空气动力学粗糙度,m;BRcd 为植被有效拖曳力系数;BRlai为直立植被叶面积指数,m2·m-1;BRsai为植被茎面积指数,是茎面积与水平地表面积的比值,m2·m-1;BZ为直立植被高度,m。
临界摩阻风速u*t由光滑平坦地表临界起动摩阻风速u*tb,地表有倒放植物引起的临界起动摩阻风速增加量u*tve和含水率引起的临界摩阻风速增加量u*twc计算得到:
沙尘物质中,能够长距离传输的PM10含量可作为起尘量的有效估计。WEPS中PM10计算方法如下:
Mann-Kendall显著性检验过程为:
式中: S表示所有正差异与负差异数量的差值;n为时间序列的总长度;xi 和xj 分别是时间序列x的第i和j个数值;sgn()为统计符号;m为序列中结(重复出现的数据组)的个数;ti 为第i组重复数据组中的重复数据个数。根据正态分布统计表,在给定显著性水平(α=0.05)下,当|Z|≤Z1-α/2时,接受原假设,即趋势不显著;若|Z|Z1-α/2,则拒绝原假设,即认为趋势显著。
式中:r12⋅34表示在控制变量x3和x4的影响后,变量x1与x2之间的偏相关系数;r12·3,r14·3,r24·3分别为排除所计算的影响因素x3后,x1与x2、x1与x4、x2 与x4之间的偏相关系数。
最后,将上述3个主要影响因子,在每个格点上建立多元线性回归模型,并对比得到标准化系数绝对值,回归系数绝对值最大的因子即为格点中的主导影响因子,模型可以表示为:
式中:b0是回归常数项;bi (i=1,2,3)是使用最小二乘法计算的标准化回归系数。分析通过95%的显著性检验,每个格点上的拟合方程对应的判定系数计算公式为:
式中:WEi 为第i个风蚀量值;WEave是风蚀量平均值;WEMLR是根据回归模型计算得到的风蚀量结果。
图22000—2023年研究区多年平均风蚀模数空间分布
Fig.2Spatial distribution of annual average wind erosion modulus in study area from 2000 to 2023
图3研究区风蚀强度空间分布
Fig.3Spatial distribution of wind erosion intensity in study area
图4研究区季节风蚀模数空间分布
Fig.4Spatial distribution of seasonal wind erosion modulus in study area in Spring (A), Summer (B), Autumn (C), Winter (D)
图52000—2023年研究区年风蚀模数变化
Fig.5Annual average wind erosion modulus changes in study area from 2000 to 2023
图62000—2023年研究区风蚀模数变化趋势空间分布
注:正负值分别表示增加和减少趋势。数字绝对值大小表示变化程度,依次为极显著、显著、轻微和不显著
Fig.6Spatial distribution of trends in wind erosion modulus changes in study area from 2000 to 2023 (Positive and negative values indicate increasing and decreasing trends, respectively. The absolute value of the numbers represents the degree of change, classified as extremely significant, significant, slight, and insignificant, in descending order)
图72000—2023年研究区季节(A)及月(B)风蚀模数变化趋势
Fig.7Trends in seasonal (A) and monthly (B) wind erosion modulus changes in study area from 2000 to 2023
图82000—2023年研究区多年平均PM10释放速率空间分布
Fig.8Spatial distribution of annual average PM10 emission rates in study area from 2000 to 2023
图9研究区2000—2023年影响因素多年平均值空间分布
Fig.9Spatial distribution of average wind speed (A), soil moisture (B), and NDVI (C) in the study area from 2000 to 2023
图102000—2023年研究区风蚀量与影响因子(风速、土壤湿度和NDVI)的相关系数(左)和偏相关系数(右)空间分布
注:星号部分通过95%的显著性检验
Fig.10Spatial distribution of correlation coefficients (Left) and partial correlation coefficients (Right) between wind erosion and influencing factors (wind speed, soil moisture, and NDVI) in study area from 2000 to 2023 (Asterisks indicate statistical significance at the 95% confidence level)
图11研究区风蚀量演变的主导影响因子(回归分析通过95%的显著性检验)
Fig.11Dominant factors driving the evolution of wind erosion in study area from 2000 to 2023(regression analysis passes the 95% significance test)
图122000—2023年研究区气候因素变化趋势
注:正负值分别表示增加和减少趋势。数字绝对值大小表示变化程度,依次为极显著、显著、轻微和不显著
Fig.12Trends of climatic factors in study area from 2000 to 2023(Positive and negative values indicate increasing and decreasing trends, respectively. The absolute value of the numbers represents the degree of change, classified as extremely significant, significant, slight, and insignificant, in descending order)
2000—2023年,河西走廊-塔克拉玛干沙漠边缘阻击战核心区的土壤风蚀总风蚀量达6.88×1010 t,多年平均风蚀模数为3 553 t·km²。该区域的风蚀强度在不同区域和季节存在差异,强烈风蚀主要在塔克拉玛干沙漠东南缘和罗布泊边缘,以及河西走廊的敦煌、瓜州等地区。季节性风蚀与年风蚀空间分布相似,其中春季风蚀模数最高,秋冬季则较低。同期,研究区PM10的平均释放量为3.11×10⁷ t,其中春季释放量为其他季节的1.6~4.3倍。
21世纪以来,研究区风蚀强度经历了减弱—增强—再减弱的变化,风蚀模数在2005年降至最低值,2010年达到峰值后逐渐下降。整体上,风蚀强度呈下降趋势,强烈及以上程度的风蚀区域面积减少了2.15×10⁴ km²,减少区域主要在塔克拉玛干沙漠中部和东南缘以及河西走廊中部地区。
研究区91%的范围内风速与风蚀模数呈正相关,风速的变化直接影响风蚀强度;而植被覆盖与土壤湿度则分别在69%和73%的区域内与风蚀量呈现负相关关系。研究期间,63%的区域风速呈下降趋势,94%的区域植被覆盖增加,98%的区域降水量上升,这些变化共同推动了风蚀量的减少。然而,全域温度升高可能导致土壤冻结期缩短,从而增加冬春干旱季节的潜在风蚀风险。因此,在风蚀防治过程中,应重视区域气候变化与生态恢复对风蚀动态的复杂影响。
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