Climate transformation to warm-humid and its effect onriver runoff in the source region of the Yellow River

The change characteristics and trends of the regional climate in the source region of the Yellow River, and the response ofrunoff to climate change, are analyzed based on observational data of air temperature, precipitation, and runoff at 10 mainhydrological and weather stations in the region. Our results show that a strong signal of climate shift from warm-dry towarm-humid in the western parts of northwestern China (Xinjiang) and the western Hexi Corridor of Gansu Provinceoccurred in the late 1980s, and a same signal of climate change occurred in the mid-2000s in the source region of theYellow River located in the eastern part of northwestern China. This climate changeover has led to a rapid increase inrainfall and stream runoff in the latter region. In most of the years since 2004 the average annual precipitation in the sourceregion of the Yellow River has been greater than the long-term average annual value, and after 2007 the runoff measured atall of the hydrologic sections on the main channel of the Yellow River in the source region has also consistently exceededthe long-term average annual because of rainfall increase. It is difficult to determine the prospects of future climate changeuntil additional observations and research are conducted on the rate and temporal and spatial extents of climate change inthe region. Nevertheless, we predict that the climate shift from warm-dry to warm-humid in the source region of the YellowRiver is very likely to be in the decadal time scale, which means a warming and rainy climate in the source region of theYellow River will continue in the coming decades.