Estimation Of The Vegetation Net Primary Productivity And Water Use Efficiency Of The Yangtze River Source Region

The Yangtze River Source Region is the type region of the high-cold ecosystem in China.Where have Unique and fragile ecosystem and especial hydrological characteristics.So,those characters have play important roll in cold' entironment, water cycle and climate system.The vegetation water use efficiency(WUE)and Net Primary Productivity(NPP)are important variables linking to the water cycle of ecosystem and carbon cycle.whose variables are important provided with signification in hydrology and ecology.The thesis is about retrieving WUE and NPP using CASA (Carnegie Ames Stanford Approach)and multi-spectral radiometric data(MODIS).To obtain temporal and spatial distribution of NPP and WUE in the Yangtze River Source Region during 200-2005 and the relation factors.The main reseach results are as follow:Fristly,Potential evapotranspiration is a component of water use efficiency.Four models were tried to calculate potential evapotranspirtion for comparison purpose,i.e. FAO Penman-Monteith,Priestley-Taylor,Hargreaves and FAO-Radiation. FAO Penman-Monteith model was chosen over others.Secondly,in thesis,analyse the temporal and spatial distribution of NPP.The rusults as follow:During 2000-2005,the annual mean NPP value between 627.39 and 713.05 gC/m².a, the total annual mean NPP value between 8.77×10¹³gC/a and 9.96×10¹³gC/a in the Yangtze River Source;from 2000 to 2003,the NPP was incresed and from 2003 to 2005,the tendency was opposite;for the change of during years.The change maximum is 41.42 gC/m²Â·a(2002-2003).For the spatial distribution,the high NPP value were main focus on the down stream of the Yangtze River Source Region,i.e. the area along river over Zhimenda station and the water net of Yequ,Moqu and Danqu,the value is above 700 gC/m²Â·a;the second-high NPP value were main focus on the southern region along Tuotuoriver and Tongtian river,the value is between 500 and 700 gC/m²Â·a;the low NPP value were main located in the regions of high-altitude and cordillera such as Tanggula mountain,Zuerkenwula mountain,Kekexili mountain and Kunlun mountain,the value is near zero.The sptial pattern of NPP distribution were relation with vegetation type,vegetaion community,altitude,climate and latitude,in Yangtze River Source Region,in the regions of high-cold meadow and high-cold grassland,the NPP value are more high than sub-alp broad-leaf and deciduous shurb and sub-tropic mountain conifruticeta.The low value'vegetaion type are focus on high-cold cushion vegetation,aparsity vegetation and non-vegetaion. About NPP value in vegetation type,the high-value type is high-cold meadow,the annual number is 682.36gC/m²Â·a,the second one is high-cold grassland,the value is 679.31 gC/m²Â·a,the value in sub-alp evergreen broad shrub is 606.79gC/m²Â·a,value in sub-tropic mountain conifruticeta is 601.13gC/m²Â·a,sub-alp broad-leaf and deciduous shurb is 597.78 gC/m²Â·a,high-cold aparsity vegetation is 577.77 gC/m²Â·a, high-cold cushion vegetation is 561.98 gC/m²Â·a.Thirdly,In this thesis,analyse the temporal and spatial distribution of WUE.The rusults as follow:During2000-2005,the annual mean WUE value between 0.83 and 1.00 gC/mm.m2, the minimum value is 0.83 gC/mm.m2(2000),the maxmum is 1.00 gC/mm.m2(2005), from 2000 to 2005,the tendency is incresingand the incresed value is 0.10gC/mm.m². For the spatial distribution,the high WUE value were main focus on the down stream of the Yangtze River Source Region,i.e.the area along river over Zhimenda station and the water net of Yequ,Moqu and Danqu,the value above 1gC/mm.m²;the second-high NPP value were main focus on the southem region along Tuotuoriver and Tongtian rever,the value between0.7and 1.0 gC/mm.m²;for the northern of river,the value below 0,7gC/mm.m²;the low WUE value were main located in regions of high-altitude and cordillera such as Tanggula mountain,Zuerkenwula mountain, Kekexili mountain and Kunlun mountain,the value is near zero.About WUE value in vegetation type,the high-value type is high-cold meadow,the annual number is 0.95 gC/mm.m²,the second one is sub-alp evergreen broad shrub,the value is 0.91 gC/mm.m²,high-cold aparsity vegetation is 0.88gC/mm.m²,sub-tropic mountain conifruticeta is 0.86 gC/mm.m²,high-cold grassland is 0.86 gC/mm.m²,sub-alp broad-leaf and deciduous shurb is 0.85 gC/mm.m²,high-cold cushion vegetation is 0.76 gC/mm.m².