Impacts of Climatic Change on Hydrological Regime in the Three-River Headwaters Region, China, 1960-2009

To identify the changing characteristics of runoff and climate change trends and their relationship in the Three-River Headwaters Region (TRHR), this study uses the runoff and meteorological data of three hydrological gauging stations and 12 meteorological stations across the TRHR for the period from January 1960 to December 2009 as the research subjects. The runoff coefficient (RC), ratio of monthly maximum/minimum runoff, and flow duration curves (FDCs) were calculated to identify spatio-temporal variations in runoff and reflect the change in hydrological regime. Results showed an insignificant decrease in annual runoff both in the Yellow River Headwater Region (YERHR) and the Lantsang River Headwater Region (LARHR), whereas it increased in the Yangtze River Headwater Region (YARHR). The RC of the three sub-regions showed a decreasing trend, the LARHR maintained a high mean value of 0.55, followed by a lower value in the YERHR (0.32), and that in the YARHR was the lowest at only 0.23. The variations in monthly maximum/minimum runoff were synchronized; their ratios were relatively steady in the study period. The flow duration analysis showed a remarkable decline in high runoff (at a frequency of 5-15%) in the three sub-regions after 1990. The runoff characteristics showed an overall decrease in the YERHR, the moderate runoff (at the frequency of 15-30% and 40-70%) of the YARHR showed an obviously increase, and the runoff of the LARHR was relatively steady. The relationship between precipitation, temperature and runoff illustrated that precipitation was the dominant factor in runoff generation, whereas the impacts of temperature on regional hydrological regime should not be neglected. Results of this study are of practical significance for water resources management and evaluation of the impacts of climatic change on the hydrological regime in a long-term consideration.