基于TVDI的黄土高原地表干燥度与土地利用的关系研究

Relationship between surface dryness degree and landuse types based on TVDI on Loess Plateau

基于地表温度和植被指数的经验关系构建地表干燥度指数。该指数对Ts/NDVI特征空间的生态特征的解释,对土壤和作物的水分含量具有一定的指示意义。通过对地表干燥度进行分级,分析陕北黄土高原区地表含水状况的空间差异,进而结合该地区的主要土地利用类型,探讨各类型的干燥度情况,并对不同地表干燥度条件下各土地利用类型对地表水分的保持能力差异进行分析,结果表明,在该区相对湿润环境中,林地以及疏林地的水分保持能力优于农地和草地,但在干旱的环境下,草地则好于林地及疏林地。建议根据不同土地利用类型的保水能力,在湿润区域增加林地的面积比例,在偏湿润区域增加疏林地的面积,在干旱区域增加草地的比例,减少农地开垦。

Vegetation coverage and surface temperature （Ts） are important parameters to describe characters of land covers. More useful information will be created by integrated analyses of these two kinds of data together, which will help us to find out main principles of the temporal and spatial variation of surface soil moisture. The present paper aims at demonstrating how Terra/MODIS data may be used to estimate spatial patterns of soil moisture, a key variable in distributed hydrological models. The basic approach is to interpret the so-called Ts/NDVI space in terms of surface ,soil moisture status. To understand the relationship between them and landuse types on the Loess Plateau, a simplified land surface dryness index （Temperature Vegetation Dryness Index, TVDI） based on an empirical parameterization of the relationship between surface temperature and vegetation index is suggested. Based on examination of Terra/MODIS image of the Loess Plateau, acquired in September, 2003, NDVI （MODll） and Ts （MOD13） are investigated as an alternative indicator of vegetation abundance and land surface temperature. Based on Landsat Enhanced Thematic Mapper Plus （ETM＋） image, the landscape classification map is conducted on supervised classification and interactive modification. To examine soil moisture conditions at the surface, TVDI is conducted with Ts and NDVI. Then, we evaluate change of TVDI under different landuse types formed by both natural and human activities. First, TVDI was divided into 10 levels to describe the spatial variability of surface soil moisture on the Loess Plateau. Second, we evaluated the water-holding capacity of each landuse type to different dryness degrees. The results are as follows： （1） Based on satellite derived information only, TVDI is conceptually and computationally straightforward, and the potential for operational application of the index is therefore large. （2）The spatial variation in TVDI reflects the variation in moisture on a finer scale than can be derived from the hydrological model in this case. （3）It can be inferred that the water-holding capacity in forestland and sparse woodland is better than farmland and grassland in relatively wet condition, and grassland is better than forestland and sparse woodland in relatively dry condition. （4） From the aspect of vegetative restoration on the Loess Plateau, according to variability of water-holding capacity in different landuse types, it could be suggested that increasing forestland and sparse woodland area in relatively wet region, increasing grassland area and reducing land reclamation in dry region can promote the process of ecological pattern optimization.