The Characteristics And Driving Mechanism Analysis Of LUCC In The Middle And Lower Reaches Of Shule River Basin

In the Shule River Basin, the precipitation is low, the evaporation is large and the ecological environment is fragile. It is a sensitive region responding the global climate change and human disturbance. In recent years, with a large number of ecological migrants continuously moving in, there was a rapid increase in agricultural population and cropland. Then, the use of agricultural irrigation water had sharply increased and the ecological water continually reduced, which led to a series of environmental problems, such as vegetation degradation, the decrease of wetland and land desertification. Given this, choosing the cities of Yumen and Guazhou in the middle and lower reaches of Shule River Basin as research subjects, to study the spatial-temporal characteristics and driving mechanism of land-use and land-cover change in the past23years based on the data interpreted from5sets of remote sensing images (1987,1996,2000,2006and2010). The main conclusions are as follows:(1) In the past23years, the area of artificial vegetation continued to expand, while the natural vegetation had been shrinking. It showed a net gain of the cropland, shrub land and urban construction land and a net decrease of the grassland, wetland and snow-ice land. And for the non-vegetation land, it increased firstly and then decreased.(2) The growth rate of urban construction land and shrub land was relatively high all the time. The cropland has been growing fast since1996. The change rate of non-vegetation land was always lowest. For the whole area, the rate of land use and land cover change was relatively low during the year of1987-1996, and then became very fast in1996-2010, which peaked between2000and2006.(3) The land use degree in the study area was not high as a whole, and significantly lower than the national average. The degree of land use changed little in1987-1996, but grew fast in the year of1996-2010. The growth peaked between2000and2006, and fell slightly in2006-2010.(4) The grassland with high coverage was transformed successively into that with medium coverage, low coverage and finally non-vegetation land. The increased shrub land was transformed from the grassland with medium and low coverage. The reduced wetland mainly changed into non-vegetation land or low-coverage grassland. The expansion of cropland benefited from the decrease in the non-vegetation land and low-coverage grassland. The non-vegetation land had a net decrease in the mutual conversion with the crop land, whereas had a net increase with low-coverage grass land. The increase in urban construction land was brought by the reduced cropland and non-vegetation land. The snow-ice land was mainly transformed into non-vegetation land when snow or ice melted.(5) The regions where the land use and land cover had changed widely dispersed, mainly concentrated in the outside of every old irrigational area. And the region with no change distributed in the inside of old irrigational area. The space distribution pattern of different types of land use and land cover change was evident. The vegetation coverage around irrigational area presented an expanding trend, but the vegetation in other area was in a degraded state.(6) The main causes of land-use and land-cover change are the rapid growth of agricultural population, large-scale agricultural development and the immigration policy. While, the natural factors, such as temperature, precipitation and annual runoff, had little influence.