Statistical properties of climatic variables in the head region of the yellow river

On the basis of the precipitation, mean air temperature, relative humidity and wind speed at 10 meteorological stations in the head region of the Yellow River from 1960-1997, the long-term monotonic trends and periods for the four climate variables have been investigated. Mann-Kendall method and wavelet transform analysis were employed to analyze changing trends and potential periods for the climatic variables. The results show that regional annual air temperature has an increasing trend while annual precipitation, relative humidity and wind speed indicate a slightly descending trend but no significant increasing or decreasing trend is identified. At principal period scale, periodical oscillation for the time series of meteorological factors are evident in the wavelet coefficients contours map. The research could facilitate the understanding of natural process and contribute to regional water resources management in the head region of the Yellow River.