Research And Development Of The Water Conservation Estimation System Based On RS And GIS In The Southern Slope Of Qilian Mountains

As one of the important functions of the terrestrial vegetation ecosystem, water conservation has many functions as the following: delaying soil erosion, adjusting earth surface runoff, purifying water quality. Estimating quantitatively and scientifically the district water conservation amount is an important gist to formulate reasonable policies of ecosystem conservation and carry out ecological engineering. In this paper, the southern slope of the Qilian Mountains Heihe upstream(Qinghai Province) and the Great River Basin are regarded as representative regions. Based on the surface water balance principles and the model of SEBAL-SCS, the district water conservation amount estimation system with the RS and GIS integration is realized by adopting ENVI/IDL + ArcGIS Engine/C#.NET secondary development and combined programming to do research and design. This system gives full play to ENVI/IDL’s ability to handle with pictures efficiently and ArcGIS Engine’s great spatial analysis and advantages of visual representation, and solves the problems such as the varities of model parameters and the complicating and overloading counting process when estimating water conservation amount, and offers a basic platform for larger scale region and long time series water conservation remote sensing supervision estimationOn this basis, by taking advantages of MODIS remote-sensing image, land-use type, soil type, observation data at the meteorological site and so on, the amount of earth surface evaporation, surface runoff and water conservation is estimated based on this system, and then, analyzing the main characteristics in different land use / coverage conditions by comparing those date. The research shows that:(1) The evapotranspiration in research area shows decline trend from the southeast area to the northwest area, and the evapotranspiration is lower in the river valley where the terrain is relatively smooth and the sea level is relatively lower; the evapotranspiration is generally larger in the mountainous region where the slope is big and the sea level is high. Average daily evaporation amount in different land use /coverage conditions ranks orderly: forest land > high coverage grassland > middle coverage grassland > naked grassland/ bare rock > lower coverage grassland > water areas(glacier/ permanent snow/ meadow and marsh > water areas) > land > impervious surface, on the whole, the earth surface evapotranspiration is relatively higher in the area with much more coverage of vegetation.(2) The average flow depth of earth surface runoff ranks orderly: impervious surface > water areas > land > forestland > bare rock > lower coverage grassland. Runoff areas are mainly located in the southeast land and impervious surface, as well as the rivers, lakes and moors in the west and northwest areas and the glacier/ permanent snow and other places. When it rains heavily, parts of the forestland and grassland can generate runoff. Usually, they hardly produce it.(3) The larger area of water conservation amount in research area is mainly distributed in the middle west of Qilian County and in northwest of Menyuan, Hui Nationality Autonomous County. From the whole, the grassland with good land vegetation coverage can store up enormous precipitation because of the interception of vegetation and buffer action even if the vegetation transpiration is obvious and the evapotranspiration is heavy. So grassland is the area where water conservation amount is much more and the ability of water conservation is much stronger, especially, the middle coverage grassland has the strongest ability to keep water.The models and parameters adopted by this article are empirical model about the relevant research and there exists certain errors for the estimation of water conservation amount. So it calls for combing the monitoring date at the surface site to make data assimilatine and further amend models and parameters, for instance, the determination on the CN value in the model of SCS and inversion of surface evapotranspiration. Therefore, this system should be further integrated into model parameters correction, analysis evaluation on the results, statistical analysis and service publication and other functions to expand the scope of application of the system region, and provide integration services platform and comprehensive solutions for larger scope and long time series water conservation amount estimation research.