Landuse And Landcover Changes And Their Environmental Effects In Shiyang River Watershed

Land use and land cover changes (LUCC) research has been the focus of global change research and has been paid great attention by scientists all over the world. It's the basic method to exploit land use changes, their driving forces and environmental effects in regional scale by RS and GIS techniques. Shiyang River Watershed locates in the east of Hexi Corridor, Gansu, Northwest China. Due to unique physiographic conditions and profound effects of human activities, Shiyang River Watershed has been facing the serious ecosystems degradation and ecological crisis, and being the typical ecological degradation area of inland watershed in the northwest China. In this thesis, multi-sources remote sensing data, digital images processing and GIS techniques were combined together to study the land use/land cover changes, and eco-function zones in Shiyang River watershed were identified. Land use was classified as six first orders and twenty-two secondary types by the means of supervised classification and visual interpret with Landsat TM /ETM~+ and CBERS images, land use and land cover changes features in last 20 years was analysed in the watershed and eco-functional zones scale. The result will provide scientific references for water resources rational utilization and eco-environmant recovery in Shiyang River watershed, and would supply land use/land cover change research at regional scale as a case. The contents and conclusions of this study were as follows:1. Land use and land cover changes in Shiyang watershed The landuse/land cover was divided into 6 first orders and 22 secondary types according to CAS land resources classification framework proposed in 1995, based on Landsat TM images in 1987, ETM~+ in 1999 and CBERS CCD 2006. The results show that the key region of land use change focused on transition zone between the oasis and deserts. The irrigated croplands increased 6% in the past 20 years, in the mean while, rainfed croplands decreased from 1999 to 2006. The cultivation occurred in outside of oasis and regions with high groundwater tables. The total farmland in Shiyang River watershed was 6.955×10~55 hm~2, increased 6%.Forest land kept steady from 1987 to 1999, and decreased recently. The sparse forest land decreased 12% and shrubs decreased 16%, mainly occurred in Minqin oasis. Grassland quality decreased, indicating by dense grassland decreased 24% from 1999 to 2006, while middle and low coverage grassland kept steady or increased a little.The areas of waterbody change slowly, but glaciers withdraw was found comparing to Chinese Glacier Inventory, the glacier area was 48km~2, decreased 25%.The town and village occupying land increased greatly, from 15% to 48% respectively. The desert decreased from 1987 to 1999, then increased from 1999 to 2006, indicating desertification trend, although the error exists in images processing and interpretations.The swarm area decreased steadily from 1987 to 2006, indicating climate warming and drying trends in the area.2. Eco-function zones in the basin Based on the topographical characteristics and the ecological functions that should be untaken in Shiyang River watershed, the watershed was divided into four eco-functional zones, including water conservation forest zones of Qilian mountains, oasis zones of corridor-basin, transitional zones of desert and oasis, and desert zone. The water conservation forest zone of Qilian mountains was subdivided into glacier-snow with low vegetation cover zone, alpine meadow, shrub and water conservation forest zone and mountain grassland and hungriness-plain zone; oasis zone of corridor-basin was subdivided into oasis city zone and oasis agriculture zone; transitional zone between oasis and desert was subdivided into Minqin oasis zone, Changning oasis zone, and Jinchuan and Hexi Pu oasis zone; desert zone was subdivided into desert zone and desert-hungriness zone. As an integrated system, the upstreams and downrivers of Shiyang River depends on each other. The upstreams is the natural reservoirs of water resource, the downriver is ecological barriers to withstand blow sand and prevent land from desertification, and oasis in the middle low reach is the key area to sustainable development of whole watershed.3. The driving forces of land use changes in the river Increasing population, which stimulate the increase of production and demand of livelihood, was the original driving force of irrigated land expanding. The Shiyang River watershed has been dominated by strong human activities, the agricultural, especially plantation dominated industrial structure determined extension-type development mode. Improvement of agricultural production techniques accelerated the expansion of irrigated land. Political and institutional factors played an important role in land use and land cover changes in the river.