Ecological environment is not only the basic needs for human survival and development, but
also the material foundation of economic and social development. With the development of society
and economy，the eco-environment problem has increased dramatically. Nowadays, its vulnerability
is one of the top concerns in global environmental change and sustainable development project, and
has attracted many scholars’ attentions.
Yanhe Basin is located in the central Loess Plateau of the northern Shaanxi province, which is a
typical gully region of Loess Hilly Region. The complex conditions there, combination of regional
natural, cultural, economic, and geographical, as well as the detrimental impact of natural disasters
and environmental destructive activities, made the basin suffers from fragile ecological environment,
serious soil erosion, and fragile ecological environment. Evaluating the ecological vulnerability of
Yanhe Basin and grasping the ecological environment and spatial pattern has a great significance to
ecological construction and the sustainable development.
Take the Yanhe Basin of Loess hilly region as study area, based on the RS and GIS technologies
and the method of spatial principal component analysis (SPCA), the integrated assessment of
eco-environment vulnerability are studied on two scales from regional to watershed, systematic
analysis of the ecological vulnerability spatial differentiation of Yan Basin. And further discuss the
vulnerability variation characteristics on a regional scale, preliminary study on its driven mechanism.
The main conclusions are as follows:
(1) Ecological environment vulnerability of Yanhe Basin was decreased as a whole, but still in a
fragile state, mainly at moderate level. Slight and light fragile areas are mainly distributed in the
southeast Baota District and Yanchang county, which is the best ecological environment quality area
in the Yanhe Basin; the moderate fragile areas are mainly located in the southeast of Ansai County,
Yanchuan County and Baota District; severe and extremely vulnerable area accounts for about 11%
of the whole area, mainly in Jingbian County, northwest of Zhidan County, northwest of Ansai
County and the part region of Zichang county. From the point of view of the overall pattern of spatial
distribution, the study area’s ecological fragility gradually decreased from northwest to southeast.
(2) Eco-environment vulnerability assessment of typical small watersheds in different
vegetation zones show that the eco-environmental vulnerability in steppe zone was at heavy level,
forest steppe zone at medial level and forest zone at light level, the ecological fragility in typical small watershed internal of the same vegetation zone are similar.
(3) The vulnerability grade of typical small watershed in different vegetation zones all showed a
certain regularity with the slope changing. Slight vulnerability was mainly distributed within 3
degree, and then appeared wavy changing trend of "decreasing - increasing – decreasing ", the other
grades increased first and then decreased with slope increasing. And all reached the maximum
between 15 degree and 35 degree. At the same time, special geomorphic features and erosion
environment, making the most ecological vulnerable areas located in gully slope.
(4) The dynamic evaluation of the time series shows that, during the period 1990-2000, the
ecological environment of Yanhe Basin showed downtrend at whole; and then gradually improved
and stabilized between 2000 and 2010. In the space level, the farther away from the city center, the
lower degree of ecological vulnerability; and farther from the river, the higher degree of ecological
(5) Adopt the mathod of space principal component analysis to study the driving force of the
ecological vulnerability in Yanhe Basin, initially determines four major driving factors are
influencing eco-ecological vulnerability in the region, that is terrain condition, vegetation cover, land
use types and meteorological factors.
Key words：Yanhe watershed, Eco-environment vulnerability, Spatial principal component analysis,
Remote sensing, Geographical information system, Spatial-temporal variation