Analysis of the Spatio-Temporal Characteristics of Water Use Efficiency of Vegetation in West China

Water use efficiency(WUE) is the ratio between the net amount of carbon absorbed by the plant(NPP) and the amount of water lost through evapotranspiration(ET).West China includes large arid and semi-arid regions and has suffered water shortage and ecosystem degradation in recent decades.Therefore,investigating the spatio-temporal characteristics of WUE for different vegetation ecosystems and identifying their distribution with low WUE and high WUE are important for the conservation and management of water and land resources in West China(73°~112° E,26°~50° N).In this paper,the Monteith type carbon model-C-FZX driven by temperature,radiation and fAPAR retrieved from remote sensing was used to estimate NPP in West China in 2002.Meanwhile,the Common Land Model(CoLM) was also applied to estimate actual ET in the same year.The input data mainly included the NCAR 6-hour and 0.9(metrological datasets,1 km IGBP land cover data,1 km USGS soil data,the global 0.25(monthly MODIS LAI data and the 1 km VGT-S10 NDVI data.Then the WUE values were estimated by the ratio of NPP to ET in each 1 km pixel.Some field measurements of WUE for different plants in West China were used for validation.The study represented the preliminary overview of WUE in West China.The total annual NPP and actual ET in West China in 2002 were estimated about 0.96 PgC and 2 098 km3,respectively.The mean annual WUE per square meter was about 0.32 gC·mm-1 m-2.Meanwhile,the annual and seasonal spatial patterns of WUE in the region were pronounced.The high WUE level mainly distributed in the northwest part of Xinjiang Region with the highest WUE reaching to 4 gC·mm-1·m-2,followed by the south corners of Tibet Region and Shaanxi province with WUE ranged from 1 gC·mm-1·m-2 to 2 gC·mm-1·m-2.The low WUE level was showed in the sandy deserts and the most part of the Tibetan Plateau with WUE ranged from 0.4 gC·mm-1·m-2 to zero.On the other hand,some arid inland river basins in West China including the Tarim River Basin,the Heihe River Basin and the Shule River Basin showed in relatively high WUE patterns,especially in the summer,indicating that some particular ecosystems living in the arid basins might have predominant function in water use efficiency.In addition,it is also investigated that the WUE properties of different ecosystems and their seasonal profiles in West China.In general,the annual WUE of the main ecosystems in West China was ranked in the order as: mountain forestdesert shrub and woodlandirrigated farmlandalpine meadowcold desert and Gobi.