Long-term Trend for Major Climate Variables and its Impact on Eco-environment in the Upper Yellow River Basin

On the basis of the mean air temperature and precipitation from 23 meteorological stations in the upper Yellow River basin from 1960 to 2001, the long term trend for major climatic variables has been investigated in this paper. The possible trends of annual and monthly climatic time series are detected by using a non parametric Mann - Kendall method. The results showed that the annual mean temperature has increased by 0.8 degrees C in the upper Yellow River basin during the past 42 years. The warmest center was located in the northern part of the basin. The nonlinear tendency for annual precipitation was negative during the same period. The declining center in annual precipitation was located in the eastern part and the center of the basin. The variation of annual precipitation in the upper Yellow River basin during the past 42 years exhibited an increasing tendency from 1972 to 1989 and a decreasing tendency from 1990 to 2001. This may result from possible climate change or the effect from human activities. At the same time, climate variability resulted in the problems of eco - environment such as decreasing of the stream flows, shrinking of the lakes, melting of the iceberg, degenerating of the pastures, deserting and losing of water and soil as well. During the past 42 years, the climate of study area becomes drier and warmer, and its variability increases, i.e. increasing of temperature and decreasing of precipitation. Therefore, climate change is considered as a basic driving factor to the deterioration of eco - environment.