Responses of natural runoff to recent climatic changes in the Yellow River basin, China

The Yellow River, the second longest river in China, experienced frequent zero flow in the lower reaches of the mainstream in the 1990s. In recent years, the zero-flow phenomenon has almost disappeared. Besides engineering measures implemented to maintain ecological flows, the changes in natural runoff might have contributed to replenish the river. In this study, we used the Soil and Water Assessment Tool (SWAT) model and runoff elasticity analyses to assess the impacts of climatic changes on the natural streamflow at the Huayuankou station. The results show that there was little increase of precipitation but substantial recovery of natural runoff in the recent period (2003–2011) compared with the low flow period (1991–2002). The recent precipitation was slightly greater (~2% of the mean annual precipitation in the baseline period of 1960–1990) than precipitation in the low flow period. However, the natural runoff in the recent period was much larger (~14% baseline runoff) than runoff in the low flow period. The decreasing runoff in the low flow period was mainly caused by the decline in precipitation while the runoff recovery in the recent period was largely affected by the contributions from the climatic variables other than the precipitation. In the recent period, precipitation could account for a reduction of 21% baseline runoff whereas the others – net radiation, wind speed, air temperature, and relative humidity – accounted for an increase of 7.5% baseline runoff. The runoff reduction (~10.4% baseline runoff) caused by the changes in temperature and relative humidity was offset by the contribution from the decreasing net radiation and wind speed which resulted in an increase of ~17.9% baseline runoff.