Hydro Climatic Trend and Periodicity for the Source Region of the Yellow River.

The hydrology of the Yellow River source region is expected to be affected by coming climate change. This will have repercussions for the 110 million basin inhabitants. Consequently, precipitation, temperature, and streamflow trends and periodicities during the last 50 years were investigated to identify significant changes in time and space over the study area. Results showed that mean annual temperature increased for all stations and it had an accelerated increasing trend during the last decade. Mean annual precipitation trends varied depending on the station; however, they were generally slightly decreasing. Annual streamflow decreased markedly, especially from the 1990s, but showed recovery during recent years. Statistically significant changes in trend occurred for temperature in 1998 and for streamflow in 1990. Based on the streamflow change point, seasonal analysis results showed that precipitation mainly decreased during the summer monsoon period (July-September) and temperature increased throughout the year. Corresponding to the weakened monsoon period the average runoff depth is decreasing by 0.74 mm=year over the whole area. Statistically significant 2- to 4-year periodicities for mean areal precipitation and temperature occurred over the area. For streamflow, an even stronger 8-year periodicity was revealed from the end of the 1960s to the beginning of the 1990s. Frequency analysis investigated the magnitudes of mean annual precipitation and discharge corresponding to a given frequency. Hydroclimatic trends and linkages at each subbasin were investigated to further improve the understanding of observed streamflow changes. The investigated results have important implications for future water availability in the Yellow River source region. [ABSTRACT FROM AUTHOR]