一种基于SWAT模型的干旱牧区生态脆弱性评价方法——以艾布盖河流域为例

An ecological vulnerability evaluation method for arid pasturing areas based on the SWAT model:a case study in the Aibugai Basin

针对干旱牧区生态脆弱性特点,以GIS为平台,利用气象、土壤、土地利用、水资源开发利用等数据,结合SWAT模型模拟结果,建立了一种基于SWAT模型子流域划分的干旱牧区生态脆弱性评价体系,对西北干旱牧区艾布盖河流域1990年、2010年生态脆弱性进行了评价。从评价结果可以看出,研究区北部及西部生态稳定性保持较好,生态脆弱等级下降主要发生在研究区的东南部,20年间耕地扩张造成的草地被侵占及水资源过度开发利用是造成生态退化的主要原因。评价体系紧紧围绕干旱牧区"水-草-畜"关系设置评价指标,将观测数据与水文模型模拟相结合,统计数据与空间地类相联系,点面结合,能够较好的反映出研究区20年间生态脆弱程度变化趋势及主要问题。

Ecological vulnerability evaluation is a prerequisite to conducting ecological restoration. The common ecological vulnerability evaluation methods have some applicability problems in arid pasturing areas： 1 ） the evaluation indicators are numerous, and the data are usually difficult to obtain; 2） an administrative region, such as a city or a country, is often used as the evaluation unit, which is too large and lacks specific significance. Commonly used data, such as meteorological data, soil data, land-use data, and water resource development and utilization data, as well as the simulation results in the SWAT model, are used in this research to build an ecological vulnerability evaluation of arid pasturing areas based on the SWAT model. Ecological vulnerability of arid pasturing areas has been divided into ecological vulnerability of the natural ecosystem and ecological vulnerability of the human-nature coupling system. Drought index, vegetation coverage, soil bulk density, and evapotranspiration capacity of soil water are used to depict ecological vulnerability of natural ecosystem; evenness index, contagion index, ecological suitability index, and water utilization modulus are used to depict the humannature coupling system. Firstly, the SWAT model has been used to divide sub-basins and hydrological simulations by the combination of observed data and simulated data, and the association of the statistic data with spatial land type. All indicators have been set based on GIS, linear piecewise membership functions have been adopted to calculate index values, and analytic hierarchy process （AHP） is adopted to determine the weighs of criteria layers and index layer. The ecological vulnerabilities of the research area are divided into five levels. This evaluation model was used in the Aibugai Basin （which is located in arid pasturing areas in Northwest China） to evaluate the change in ecological vulnerability caused by land-use variation between 1990 and 2010, and 17 sub-basins were divided according to demand. The results showed that, during a period of 20 years, both the entire research area and each sub-basin went through a CIEV （comprehensive index of ecological vulnerability） decrease to some degree. Sub-basin 9, 10, 11, 12, and 15 developed a moderate vulnerability level from a slight vulnerability level in 1990, and sub-basin 16 andl7 have changed to a sever vulnerability level from a moderate vulnerability level in 1990. The CIEV of the entire research area decreased to 0.59 in 2010 from 0.70 in 1990. The northwestern part of the research area had better ecological stability, and the degradation in ecological vulnerability levels took place mainly in the agro-pastoral ecotone located in the southeast of the research area. With the expanding demands of grain and cattle, agricultural areas have gradually expanded northward in the past 20 years. Declines in grassland areas and overdeveloped water resources caused by farmland expansion were the main reasons that caused the ecological degradation in the research area. Closely tied to the relationship with water, grass and cattle in arid pasturing areas to establish indicators, this evaluation model effectively reflected the aggravation of ecological vulnerability caused by cropland expansion in the research area from 1990 to 2010.