黄土丘陵沟壑区生态风险时空动态及其风险分区—以陕西省米脂县为例

目前,黄土丘陵沟壑区等生态脆弱区生态风险评估已成为地理学与生态学应对生态系统管理的研究热点之一。以黄土丘陵沟壑区米脂县为研究区,构建“风险概率—敏感性—损失度”（PSI）的三维评价框架,并以子流域为评价单元进行数据整合,分析了米脂县2009-2015年准则层与综合生态风险的时空分异及其重心转移,并基于风险主导因子给出米脂县风险防范分区及降险对策。结果如下：（1）2009-2015年风险概率分别为49.93%、52.92%,有上升趋势;生境敏感性分别为0.61、0.60,下降了1.6%,生境质量趋好;损失度分别为0.42、0.46,损失度增加。（2）生态风险呈现中间高南北低的空间分布;研究期间生态风险值分别为0.14、0.15,风险有所升高;风险重心向西南转移跃入银州川道且风险演化主体方向为西北—东南走向。（3）风险预警区、生态恢复区、预警恢复兼顾区、自然调控区面积占比分别为7.53%、6.57%、23.86%、62.04%。基于风险主导因子的风险防范分区可有效进行风险消解,促进区域生境的可持续。

Spatio-temporal variation of ecological risk in the loess hilly-gully region and its precaution partitions: A case study of Mizhi county,Shaanxi province,China

Ecologically fragile regions such as loess hilly-gully region are highly responsive to global change. Regional development is on an unsustainable track under the background of fragile ecological environment and agricultural activities. The study of ecological risk in this region has become one of the hot spots of geographical and ecological response to ecosystem management. Taking Mizhi county for the study of loess hilly-gully region, land-use maps of this county in 2009 and 2015, a digital elevation model (DEM) and social and economic statistical yearbook of Mizhi county were needed and 253 small watersheds were identified as the auxiliary evaluation units by using ESRI's Hydrological Analysis Tools for ArcGIS 10.2. A comprehensive ecological risk assessment framework for identifying risk probability, habitat sensitivity, and system impairment was established, and multi-source data were integrated through range standardization and entropy weight method at watershed level. The spatio-temporal differentiation of criteria layers and comprehensive ecological risk were analyzed, at the same time, the evolution trend of comprehensive ecological risk was explored through the Standard Deviation Ellipse (SDE) and risk gravity. The risk precaution partitions were simultaneously delineated based on the risk dominant factor and the risk management strategies were formulated. The results were as follows: (1) The spatial distribution pattern of risk probability in Mizhi county was generally high in the middle and east and low in the northwest. The value of risk probability increased from 49.93% to 52.92% during 2009-2015. The habitat sensitivity index was 0.61 in 2009 and 0.60 and 2015, respectively, which was a decrease of 1.6% based on the InVEST model, and the habitat quality improved. The system impairment index was generally higher in the central and western regions while lower in the eastern region (southeast and northeast). The impairment index increased from 0.42 to 0.46 during 2009-2015, which indicated that the degree of impairment caused by ecological risk increased. (2) The spatial distribution pattern of comprehensive ecological risk was high in the middle, while low in the south and north. Between 2009 and 2015, the ecological risk index increased from 0.14 to 0.15, with an increase of 7.14%. The risk gravity of Mizhi county was distributed in Gaoqu township in 2009, and jumped into Yinzhou township in 2015. The main ecological risk evolution was northwest-southeast trending, and kept stable basically. (3) The study area was divided into four types of risk precaution partitions. Risk monitoring zones, ecological recovery zones, monitoring and recovery zones, and natural regulation zones encompassed 7.53%, 6.57%, 23.86% and 62.04% of the study area, respectively. Risk precaution partitions based on risk dominant factors can effectively eliminate risks and promote the sustainable development of regional habitats.