Rs And GIS Aided Study On Ecological Water Requirement Of Plant-soil Composite System At Multi-scale In The Guanzhong-Tianshui Region

Water is the source of life,the need of production,and the foundation of ecology.It plays an important role in ecological construction,production and life.In the traditional allocation of water resources,water resources are given priority to irrigated agriculture,industry,and residential life.Ecosystem water use is generally ignored or crowded out.Since the 1990 s,research on ecological water requirement has become a hot topic in eco-hydrology and water resources management.At present,research on ecological water requirement is mainly directed at a single ecosystem,and the critical threshold of water requirement for complex ecosystems needs further study.The plant-soil composite system is an important part of the ecosystem,and it is the center of material circulation and energy transfer in the ecosystem.The GuanzhongTianshui Economic Zone as the important strategic link of "the Belt and Road",is one of the three key economic zones proposed in the "11th Five-Year Plan" of the Western Development of China.Therefore,the plant-soil composite system in the Guanzhong-Tianshui Economic Zone is selected as the research object.Firstly,the boundaries of the third-level watershed are extracted based on the DEM data,the spatial distribution maps of plant and soil texture types are obtained based on the Landsat remote sensing images and the soil texture data.Then,the corresponding mathematical models are used to evaluate the minimum ecological water requirement of the plant-soil composite system.Also,the tempo-spatial distribution characteristics are analyzed based on RS and GIS technologies at the landscape scale and the third-level watershed scale.The study offers scientific references for making the target of the regional hydrological ecological environment protection and has a reference significance for the rational allocation of water resources.The main research results are as follows:(1)According to the Land Use/Land Cover Change(LUCC)classification criteria and the spectral and texture characteristics of remote sensing images,we divide the land cover into woodland,arable land,grassland,waters,construction land and unused land.From 2000 to 2015,the areas of woodland and construction land increased obviously,while the areas of arable land and unused land decreased.These changes indicate the ecological improvement and economic development.(2)Based on the classification results of the Temperature Vegetation Drought Index(TVDI)obtained by the constructed Land Surface Temperature-Normalized Difference Vegetation Index(Ts-NDVI)feature space,the arid and semi-arid regions in the study area are mainly distributed in the northeast and central part of Guanzhong,the humid and semi-humid regions are mainly distributed in the south of Guanzhong and the north and south of Tianshui.(3)The tempo-spatial differences of the ecological water requirement at the landscape scale in the Guanzhong-Tianshui Economic Zone are obvious.At the temporal scale,due to the large-scale increase of urban construction land,the area of plant-soil landscape area in the study area has decreased,the total minimum ecological water requirement of the corresponding growth period has also decreased.At the spatial scale,the landscape types of higher ecological water requirement per unit area are woodland-clay loam,woodland-loam,woodland-sandy loam and woodland-gravel loam,the landscape types of lower ecological water requirement per unit area are grassland-clay loam,grassland-loam,grassland-sandy loam and grass-gravel loam.(4)The tempo-spatial differences of the ecological water requirement at the third-level watershed scale in the Guanzhong Tianshui Economic Zone are larger.At the temporal scale,in addition to the Weihe watershed(Jinghezhangjiashan above)and the Weihe watershed(Beiluohezhuangtou above),the total minimum ecological water requirement for the third-level watersheds in the rest of the study area has been reduced.At the spatial scale,the minimum ecological water requirement per unit area in the Weihe watershed(Jinghe Zhangjiashan above)located in north and Jialingjiang watershed located in south region of the study area is relatively high,and the minimum ecological water requirement per unit area in the Xianyang to Tongguan watershed located in central region is relatively low.