Journal of Geographical Sciences ›› 2011, Vol. 21 ›› Issue (4): 594-608.doi: 10.1007/s11442-011-0866-1

• Climate Change • Previous Articles     Next Articles

Identification of dominant climate factor for pan evaporation trend in the Tibetan Plateau

LIU Xiaomang1,2, ZHENG Hongxing1, ZHANG Minghua2, LIU Changming1   

  1. 1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China;
    2. Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA
  • Received:2011-02-25 Revised:2011-03-18 Online:2011-08-15 Published:2011-08-05
  • Supported by:

    The European Commission (Call FP7-ENV-2007-1), No.212921; National Basic Research Program of China, No.2010CB428406

Abstract:

Despite the observed increase in global temperature, observed pan evaporation in many regions has been decreasing over the past 50 years, which is known as the "pan evaporation paradox". The "pan evaporation paradox" also exists in the Tibetan Plateau, where pan evaporation has decreased by 3.06 mm a-2 (millimeter per annum). It is necessary to explain the mechanisms behind the observed decline in pan evaporation because the Tibetan Plateau strongly influences climatic and environmental changes in China, Asia and even in the Northern Hemisphere. In this paper, a derivation based approach has been used to quantitatively assess the contribution rate of climate factors to the observed pan evaporation trend across the Tibetan Plateau. The results showed that, provided the other factors remain constant, the increasing temperature should have led to a 2.73 mm a-2 increase in pan evaporation annually, while change in wind speed, vapor pressure and solar radiation should have led to a decrease in pan evaporation by 2.81 mm a-2, 1.96 mm a-2 and 1.11 mm a-2 respectively from 1970 to 2005. The combined effects of the four climate variables have resulted in a 3.15 mm a-2 decrease in pan evaporation, which is close to the observed pan evaporation trend with a relative error of 2.94%. A decrease in wind speed was the dominant factor for the decreasing pan evaporation, followed by an increasing vapor pressure and decreasing solar radiation, all of which offset the effect of increasing temperature across the Tibetan Plateau.

Key words: pan evaporation trend, reference evapotranspiration, attribution, the Tibetan Plateau