Landscape Ecological Risk Study Of Shiyang River Basin Based On GIS And RS Approach

With the fast development of global urbanization and strengthening of natural environment change, the human-nature coupling system research has been paid much attention. For the past a few years, due to China's rapid economic growth, the mode of high energy consumption, resources and labor intensive, the ecological environment has been seriously degenerated, particularly for the fragile region. That has threatened to human life and the sustainable development of social economy, and has become the hot issue. River basin that acts as a kind of complex natural geographical area has been affected by natural factors and human activities profoundly, and then, pressure and stress of landscape ecological system has becoming more serious.The Shiyang river basin has a characteristic of strong solar radiation, abundant sunshine, large temperature difference, less precipitation, strong evaporation and air drying, and has becoming the highest level of the development in soil and water resources in the Hexi corridor. Ecological degradation and crisis are the primary maters should be taken much attention. The major problems including forest area reducing and snow line rising, surface water decreasing and underground water level declining, destruction of grass and water loss and soil erosion, water pollution and water quality deterioration, vegetation degradation, downstream of intensified desertification etc. have negative effects for the sustainable development of economy and society, especially for the midstream and downstream region in which the ecological environment has deteriorated gradually and the landscape types also have changed obviously.Therefore, the study in Shiyang river basin about effective evade of landscape ecological risk, the initiative adaption and integrated management has become hot and key issue on ecosystem comprehensive evaluation. Landscape ecological risk study will provide some references on ecological construction, resource management, environmental recovering and assessment for the establishment of related plans and policies at the present stage.This paper based on theories of the landscape ecology and landscape ecological risk, different periods of remote sensing image data as underlying data source, as well as the data of natural geography, meteorology and human data, etc., the index of landscape ecological risk were built through the method of GIS and RS to analyze and evaluate landscape ecological risk, also reflect characteristics of landscape ecological risk. The main results show as follows:(1) The number of landscape types had changed profoundly from 1986 to 2014. The area of farmland, grassland and construction land increased by 257.15 km2, 303.12 km2 and 257.15 km2 respectively. While the area of forest land, water and unused land reduced 89.69 km2, 232.37 km2 and 73.26 km2. And, the increasing of construction land was most obvious, with a increase rate of 73%. The overall indexes of landscape fragmentation increased, especially in Qilian Mountains, Wuwei and Minqin oasis, where indexes of landscape fragmentation was much higher than other places. Isolation indexes also increased obviously, its rise from big to small in the order is: water > construction land > forest land > farm land > unused land > grassland, the high isolation indexes areas mainly distributed in oasis region of the upstream, middle stream downstream watershed. Before 2000, landscape superiority indexes had a little decrease, with much increase later, Wuwei and Minqin oasis were the typical areas. From all above, the research results show that the connectivity between the landscape types patches reduces, landscape instability increases, and persistence reduces.(2) The ecological fragile degree and ecological loss degree had gradually increased as a whole and the spatial differentiation was also obviously from 1986 to 2014, including south Qilian mountain, Gulang county, Wuwei oasis, Changning basin and Minqin oasis. While the ecological fragile degree and ecological loss degree in Minqin county increased at first and decreased subsequently. The above results suggest that periodic achievements of ecological environment governance have been made in the Minqin county. Governance effects in other places are not obvious, because the ecological restoration is a long-term project and different governances exist in different places.(3) Landscape ecological risk had increased gradually from 1986 to 2014. The landscape disturbance index and ecological fragile degree was much lower in upstream, while that was high in midstream, and much higher in downstream. Through transfer matrix between landscape ecological risk levels can be seen that the landscape pattern change and the ecological environment deteriorated seriously due to the growth of population and fast development of economy before 2000, then, the deterioration speed decreased, and certain recovery achievements had been obtained.(4) The landscape ecological risk in Shiyang river basin had been the obvious characteristics of homogeneous agglomeration and heterogeneous separation from 1986 to 2014. If there was high risk, then the risk was also high in the surrounding. Thus there was low risk, also the risk was low in the surrounding. The "hot spot" zones which were mainly distributed in Wuwei oasis, Minqin oasis, Gulang county kept expanding gradually, in where the landscape ecological risk risen. The "cold spot" zones were mainly distributed in Sunan and Tianzhu counties of Qilian maintain, the area was increased gradually, and the appearance of polarization was obvious.