| Impacts of land use/cover change (LUCC) on hydrological cycle, and its derived resources and environmental problems, have been a hot topic in current studies. The Guanting gorge part of Yongding River watershed, located in the mountainous area of Northern China is confronted with a fragile environment. And it is going to be rehabilitated to form the "green eco-corridor for the west part of Beijing" and "ecological barrier for the whole municipality". Meanwhile, rapid industrialization and urbanization, and the needs for higher living standards of people aggravate the situation of water shortage. In the watershed, LUCC become an important driving-forces to change the hydrology within, besides the impact of upstream. There is theoritical meaning for further studies on LUCC to discuss the impacting factors, such as natural conditions, human activities, location and so forth on LUCC, as well as related hydrology and water resource effects. It’s also can provide practical methods for ecological conservation in upstream regions, control of the impact of ecological water on water consumption in downstream areas, as well as the establishment of reasonable structure and pattern for land use/cover and scientific ecological compensation system.In this research, Yongding River watershed (in Beijing Mentougou District) was selected as a typical area in the mountainous areas of northern China. And comprehensive geographic information database was built with the help of remote sensing (RS) and geographic information system (GIS) technologies, under the guidance of natural geography, systems theory, landscape ecology and "natural-artificial" dualistic circulation etc. With the synthesized data, analyses of regional LUCC, vegetation cover change and response of precipitation were carried out. Furthermore, Impacts of LUCC on hydrology and water resources were discussed on the support of SWAT model to find out proper land use and ecological conservation methods according to the characteristics of natural resources in the mountainous areas of Beijing and local socioeconomic conditions.The main conclusions are drawn as follows:(1) Altitude, slope, geology and soil make up the foundation of the spatial pattern of land use and land cover in Mentougou District. As a location-sensitive driving force to LUCC, socio-economy factors diversify and complicate the changes in different geographical areas. Hilly areas dominate Mentougou District, which determine that woodland is base of land use/cover pattern. Within which, Forest and shrub distributes in the inner and shallow parts respectively. In piedmont plain areas, multi-purpose development activities exist for the trivial topographical limitation, where agricultural and urban landscapes make up the most part. The main transformation from unused land to shrub land is the main direction in inner mountainous area. The main transformation of land use structure is shrub land and unused land to forest and construction land in shallow mountainous area and piedmont plain area. Because of improvement of transportation infrastructure and construction land sprawl agricultural landscape is becoming fragmental and marginal, which sharply abate the dominance of cultivated land.(2) Land use/cover images of Mentougou District of1984,1992,1999and2010were derived from satellite imaginaries. The results were concluded based on the analysis of these data. Cultivated land area has been decreased. Construction land (including urban land, rural residential land, industrial and mining land) area has been increased, which occurred in downtown and fringe belt of Mentougou District. The area of shrub and forest are totally increased. Average values of GIMMS-NDVI of the whole region are ranged from0.347to0.439. In general, the NDVI values increase with the fluctuations of rainfall in recent years These data indicate that greening rate and vegetation coverage are increasing during the afforestation programs and ecological restoration.(3) The Horizontal differentiation characteristics of velocity of land cover change and vegetation interannual variation in Mentougou District over the last decade, indicates that land cover change is determined by rainfall, topology and human activities etc. In general, with less of human disturbance and enforcement of ecological conservation and remediation, MODIS-EVI is becoming better, in spite of the descending of rainfall in recent decades.Although rainfall is decreasing in study area, water stress in low-lying and good catchment condition positions is weaken due to the redistribution of precipitation by terrain factors and the further weakening of human activity and the large area promotion of MODIS-EVI by ecological remediation project. Land cover is relatively stable in west zone where elevation is higher and slope gradient is bigger. MODIS-EVI is decreasing in some places of piedmont plain area and Junzhuang Town and Tanzhesi Town on account of construction land occupying other land types. Fluctuations of land cover are also much bigger in these places.(4) Time lag effect of rainfall to vegetation is within1month in Mentougou District. Affect aging concentrates between1to2months because of limitation of soil water content with high mountains and steep slopes. Because forest land and orchard land with gentle slope and thickness soil layer are better in conserving water than shrub land and grass land, the affect aging of rainfall to forest land and orchard is much longer than that of shrub land and grass land. While the recovering habitats levels are evolving from low1to high from unstable to stable in our study area, maximum correlation coefficient between rainfall and land cover is increasing. Degree of dependence and utilization efficiency of shrub to rainfall is strengthened. The degree of response of vegetation to rainfall will be strengthened in the condition of less human disturbance.(5) SWAT model was applied to simulate hydrologic water cycle in mountain region on the basis of vegetation coverage (NDVI) derived from remote sensing data, satellite imaginaries, With the increasing of vegetation cover area and the improvement of vegetation coverage grade, direct surface runoff is decreasing in Mentougou District, and this region goes through the change from the water riching dominant zone to the water shortage dominant zone. Along the topographic gradient from remote mountainous area, shallow mountainous area, to piedmont plains area, the conveyance of runoff water from mountainous area to plain area is reducing. Decreasing of rainfall, increasing of vegetation coverage area, improvement of vegetation coverage (NDVI) are direct reasons of the significant decrease of runoff in remote mountainous area, topographical factor and human activity interventions are indirect influence factors by influencing the land use/cover. In shallow mountainous area, the weakness of runoff yield’s consumption are not induced by the changes of precipitation but by the changes of underlying surface conditions and intervention degree of artificial side-branch water cycle under the social and economic surge. The improvement of vegetation coverage degree (NDVI) is the main cause of the runoff yield’s decrease.(6)To study the changes of hydrology and water resources, we should not only consider the human disturbance on land use/cover change, but also take the topology into account and analysis its effects on water resources’ redistribution. Therefore, the division of geographic unit according to topology is necessary. As to ecological protection and ecological remediation, a whole consideration of how to allocation water resources among ecological water utilization, production water and domestic water demands, and between upper reaches and lower reaches is essential from the theory of system theory, land landscape ecology. Only in this way, a pattern of land use/cover which is suitable to local climate and topology conditions and meeting the demand of local economical and social development could possibly be constructed. |
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