Climate-induced hydrologic change in the source region of the Yellow River: a new assessment including varying permafrost

Abstract. The source region of the Yellow River (SRYR) provides 35 % of the rivers annual discharge but is very sensitive to the climate change. The change in discharge from the SRYR has been attributed to both climatic and anthropogenic forces, and previous estimates of the impact of human activities on the change in discharge have been higher than 50 % of the total change. Considering the very low population density and limited land use change, this result is potentially inconsistent. Our study modifies the traditional Budyko separating approach to identify and quantify the climatic causes in discharge changes. Application of this new approach to the SRYR now highlights the role of the degrading permafrost, based on long-term observation data of the maximum frozen depth (MFD). Our results show that over the past half-century, the change in discharge in the SRYR was primarily controlled by climate change rather than local human activities. Increasing air temperature is generally a negative force on discharge whereas it also causes permafrost to degrade – a positive factor on discharge generation. Such conflicting effects enhance the uncertainty in assessments of the hydrological response to climate change in the SRYR.