Impacts of Climate Change on Surface Hydrology in the Source Region of the Yellow River

Abstract:

The source region of the Yellow River contributes about 35% of the total water yield in the Yellow River basin playing an important role for meeting the downstream water resources requirements. Hydroclimatic trend and periodicity 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 station location; 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 60s to the beginning of the 90s.

Summer precipitation trends and teleconnections with global sea surface temperature (SST) and Southern Oscillation Index (SOI) from 1961 to 2010 were investigated. The summer precipitation in the whole region shows statistically significant negative correlations with the central Pacific SST for 0-4 month lags and with the southern Indian and Atlantic Ocean SST for 5-8 month lags. Analyses of sub-regions reveal intricate and complex correlations with different SST areas that further explain the summer precipitation variability. The SOI had significant positive correlations mainly for 0-2 month lag with summer precipitation. It is seen that El Niño Southern Oscillation (ENSO) events have an influence on the summer precipitation, and the predominant negative correlations indicate that higher SST in equatorial Pacific areas corresponding to El Nino coincides with less summer precipitation in the source region of the Yellow River.