Acta Geographica Sinica ›› 2009, Vol. 64 ›› Issue (3): 303-314.doi: 10.11821/xb200903005

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Water and Heat Balance and Water Use of Shrub Grassland and Crop Fields in Lhasa River Valley

YIN Zhifang,OUYANG Hua,XU Xingliang, SONG Minghua,DUAN Deyu,ZHANG Xianzhou   

  1. Institute of Geographic Sciences and National Resources Research of CAS,Beijing 100101,China
  • Received:2008-10-12 Revised:2009-01-07 Online:2009-03-25 Published:2009-03-25
  • Supported by:

    National Basic Research Program of China,No.2005CB422005;The prophase research item of the Key Basic Research Project,No.2005CCA05500

Abstract:

More and more natural vegetation land has been transformed into crop fields in the Lhasa river valley on the Tibetan Plateau with the local population growth and economic development. However, the land cover changes would exert great impact on ecosystems energy and water balance and water use. We did experiments in crop fields at Lhasa Plateau Ecosystem Research Station and the nearby shrub grassland. Then we researched the water and energy balance and the processes of water extraction from roots using SHAW model based on experiment data and climatic data obtained at Lhasa Plateau Ecosystem Research Station. By the analysis of the simulated results, some main conclusions were drawn as follows. (1) Net radiation received by crop fields was more than shrub grassland; and the outgoing latent heat from crop fields was dominating, with the all-year Bowen ratio being 0.29. As for the shrub grassland, the all-year Bowen ratio was 0.89. The outgoing latent heat of shrub grassland was 53% of crop fields. Thus, shrub grassland limited evapotranspiration to some extent. (2) The water consumed of crop fields was nearly twice of that of shrub grassland. Irrigation resulted in much deep percolation and increased soil evaporation. (3) The deep soil water supply and root extraction indicated that shrubs could absorb deep soil water that could not be used by crops.

Key words: Lhasa river valley, shrub grassland, crop fields, SHAW model, water and heat balance, root extraction