Spatial and temporal variations in vegetation index and its impact factors in the West Liaohe Plain in Inner Mongolia
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摘要:
西辽河平原位于我国北方农牧交错带，属半干旱气候，发育科尔沁沙地，生态环境极其脆弱，开展植被指数时空变化及其影响因素研究，对于预测土地退化风险意义重大，可为该流域生态环境保护治理及水资源合理开发利用提供技术支撑。利用2000—2019年MODIS NDVI数据，采用一元线性回归趋势法和Mann-Kendall检验分析了近20年来该地区的植被生长变化趋势及突变情况。从影响植被生长的水热条件出发，分析了NDVI值与气象因素（降水、气温）、土壤湿度、地下水埋深等因子的相关关系；结合人类活动，分析了土地利用类型变化对NDVI值的影响。结果表明：（1）2000—2019年生长季NDVI值整体呈上升趋势，不存在显著突变点，最高值0.56，最低值0.41。（2）NDVI值在空间上呈现“东高西低”的分布特征，不同用地类型的NDVI值由大到小依次为耕地>林地>沼泽地>滩地>草地>盐碱地>沙地。（3）92.5%的区域植被呈增长趋势，7.5%的区域植被呈减少趋势。（4）NDVI值与降水、气温、土壤湿度呈正相关关系，相关系数分别为0.86，0.78，0.81，降水对植被影响最大。（5）最适宜天然植被生长的地下水埋深约为3 m，当地下水埋深大于10 m时，NDVI值会随着埋深的增加剧烈减小。（6）人类活动如土地开垦、植树造林是近20年来NDVI值呈增加趋势的主要原因之一，在一定程度上改善了当地生态环境。
Abstract:The West Liaohe Plain is located in the farming-pasturing ecotone in North China, which lies in the semi-arid region, including the Kerqin Sandy Land, where the ecological environment is extremely fragile. It is of great significance to study the spatio-temporal variation in vegetation index and its influencing factors for predicting the risk of land degradation, which can provide technical support for the protection and management of ecological environment and the rational development and utilization of water resources in the watershed. In this paper, based on the MODIS NDVI data from 2000 to 2019, the univariate linear regression trend method and Mann-Kendall test are used to analyze the vegetation growth trend and mutation in this area in the past 20 years. Considering the water and heat conditions affecting vegetation growth, the correlations between NDVI and meteorological factors (precipitation, air temperature), soil moisture, groundwater depth and other factors are analyzed. In addition, combined with human activities, the impact of land use type change on NDVI is analyzed. The results indicate that (1) the NDVI during the vegetation growing season from 2000 to 2019 shows an overall upward trend, with no significant abrupt change points, the highest value is 0.56 and the lowest value is 0.41. (2) NDVI presents a spatial distribution characteristic of “high in the east and low in the west”. The NDVI of different land use types are in the descending order: cultivated land > forest land > swamp land > flood plain > grassland > saline land > sandy land. (3) The 92.5% of the area shows an increasing trend, and the 7.5% of the area shows a decreasing trend. (4) NDVI is positively correlated with precipitation, temperature and soil moisture, with correlation coefficients of 0.86, 0.80 and 0.81, respectively and precipitation has a greater impact on vegetation. (5) The most suitable groundwater level depth for natural vegetation growth is about 3 m, and when the groundwater level depth is more than 10 m, NDVI will decrease sharply with the increasing groundwater levael depth. (6) Human activities such as land reclamation and afforestation are the main reasons for the increasing trend of NDVI in recent 20 years, which improves the ecological environment to a certain extent.
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Key words:
- NDVI /
- trend /
- air temperature /
- precipitation /
- soil moisture /
- groundwater depth /
- land use
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表 1 研究区2000和2018年土地利用类型面积统计
Table 1. Area of different land use types in the study area in 2000 and 2018
/km2 地类 2000年 2018年 变化 耕地 17 186 19 059 1 873 林地 2173 3485 1312 草地 24060 19873 −4187 水域 1152 569 −583 建设用地 1303 1521 218 滩地 306 471 165 沙地 6199 7066 867 盐碱地 3273 3053 −220 沼泽地 1 967 2518 551 裸土地 3 7 4 总计 57622 57622 0 
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