Study On The Vegetation Ecological Water Requirement In The Heihe River Basin Based On3S Technology

Heihe is a river basin which has a dry climate, scarce precipitation, abundant sunny, greatday-night temperature difference and extreme drought in the middle and lower reaches. Inrecent years, as the growth of population, and the backward of technology and managementlevel, the predominant agricultural economic activities lead to serious waste of water resources,requirement excess the ability of this basin, hence, the ecological environment is degradationconstantly. Therefore, it has a great significance of study the ecological water demand ofHeihe river basin, to achieve the rational allocation of water resources, to promote thesustainable development of ecological. This research based on the calculation method ofnatural vegetation ecological water demand put forwards by the international food andagriculture organization (FAO), applies the3S technology to connect the observed data,meteorological data and the remote sensing image and DEM digital elevation. The mainresults are as follows:(1)The within year distribution of reference crop evapotranspiration mainly shows: theminimum always occurs in January and December, it’s arranges from10mm to50mm; themaximum always occurs in June, July or August, it’s arranges from118mm to288mm, andthe total of the three months accounts for37%to46%of the ET0throughout the year.According to the spatial analysis, the annual distribution of ET0shows an incremental trendstep by step from upstream to downstream in the whole basin. During the upstream stations,Yeniugou, Tuole, Qilian and Gangcha have lower annual ET0which less than900mm, and thelowest value is725mm of Yeniugou. During the downstream stations, Jinta, Dingxin,Mazongshan, Yumen, Ejinaqi and Guaizihu have higher annual ET0which more than1100mm, and the highest value is1644mm of Guaizihu.(2)Use the developed inversion model, combining with the meteorological temperaturedates, to inversion the surface soil moisture content. And the result shows the surface soilmoisture content average from7%to12%in the basin. The average monthly values of waterstress coefficient Ks from February to October are:0.18,0.08,0.18,0.22,0.28,0.36,0.26,0.33,0.26, it suggests Ks is higher from June to September while the space distributionappears a great diversity during the different months.(3)Dominantly, In the Heihe basin, there are seven kinds of plants including forest, open forest, bush, desert, crop, high coverage grass and medium coverage grass. Among the initial,development, mid-season and late season stage the mid-season stage has a higherevapotranspiration than others, and the percentage of it is:65%of forest,81%of open forest,77%of bush,59%of desert,55%of crop,59%of high coverage grass,35%of mediumcoverage grass. And the other stages are varies by different plants. In the whole growing stage,the vegetation ecological water requirement is:16.37to17.35billion m3in upper reaches,29.75to31.22billion m3in middle reaches,8.00to8.83million m3in lower reaches, and54.12to57.32billion m3in the whole basin. According to space distribution analysis, theevapotranspiration has a growing trend from upstream to downstream, while, the ecologicalwater requirement descending from upstream to downstream.(4)The average effective rainfall of stations of wet year, normal year and dry yeararranges from: upper reaches296mm to338mm, middle reaches90mm to150mm, lowerreaches25mm to45mm. And it shows, the upper reaches can offer the water requirements ofall kinds of plants; the middle reaches can satisfy a few kinds of plants, for example, thestation Shandan, Yongchang, Zhangye, Minle can supply the desert and medium coveragegrass land, and Sunan, Minle can supply the forest land, and the reat stations the rest plants areall short of water in different degrees; at last, the lower reaches can not offer any plant of thewater demand. And the vegetation ecological water deficits are varies as the area: middlereaches5.77to10.81billion m3, lower reaches5.73to7.36million m3, and the whole basin11.50to18.17billion m3. And the Spatial distribution of lack of water quota express in thesame way as the ET0, while the volume of water shortage higher in the middle and lowerreaches, lower in the upper reaches.