Quantitative assessment of climate change and human impacts on long-term hydrologic response: a case study in a sub-basin of the Yellow River, China

In this study we developed an impact factor formula (IFF) to quantitatively attribute separately the impacts of climate change and local human activities on hydrological response (i.e. run-off) in a sub-basin of Yellow River for the period 1950-2000.Using the daily climatic data, we first calibrated and verified the variable infiltration capacity (VIC) hydrological model to the baseline period 1955-1970. Then we developed the basin's natural run-off for the following three decades (1971-2000) using the VIC model without considering local human impacts, as the VIC model is benchmarked by the 1960's hydrological regime. On the basis of observed precipitation, run-off and reconstructed natural run-off data from 1971 to 2000, we quantified their long-term trend, decadal and annual variations. Using daily climatic observations, we showed that the precipitation and run-off have decreased from the baseline decade, the 1960s, indicating a drier hydrological regime for recent decades. We further applied the IFF to quantitatively attribute separately the impacts of reduced precipitation and increased temperatures from climate change and then of local human activities on hydrological run-off response. It was found that climate change has a greater impact than human activities on the basin's run-off for the three consecutive decades. The pCC (percentage change of run-off due to climate change impact) is found to be 89% followed by 66% and 56% in 1970s, 1980s and 1990s, respectively. Over the decades, pHA (percentage change of run-off due to human activities) has continuously increased from 11% to 44%. If the trend continues, in future, the pHA is going to outweigh pCC in this basin. This study provides a quantitative assessment methodology for water resources managers to understand the changing process of the hydrological cycle and attribute its causative factors in a sub-basin of the Yellow River. Copyright (C) 2009 Royal Meteorological Society