A New Assessment of Hydrological Change in the Source Region of the Yellow River

Abstract

Hydrological responses to climate change are a widely concerning question, particularly for the source region of the Yellow River (SRYR), which is sensitive to climate change and is widely underlain by frozen ground. In considering climate change impacts on catchment properties, the traditional separation approach based on the Budyko framework was modified to identify and quantify the climatic causes of discharge changes. On the basis of the decomposition method, the traditional separation method and the modified separation method were used to analyse the discharge change in the SRYR. Using the observed annual maximum frozen depth (MFD) to indicate the frozen ground level, the impacts of frozen-ground degradation on the discharge change were further considered using the modified separation method. Our results show that the traditional separation approach underestimated climate-induced discharge change; over the past half-century, the discharge change in the SRYR has been primarily controlled by climate change. Increasing air temperature is generally a negative force on discharge generation; however, it also causes frozen ground to degrade-a positive factor for discharge generation. Such conflicting effects enhance the uncertainty in assessments of hydrological responses to climate change in the sub-basins with widely distributed permafrost.

Climate Change Impacts on Cold Season Runoff in the Headwaters of the Yellow River Considering Frozen Ground Degradation

“…Precipitation and rain increased by 12.12% and 16.09% in the 21st century. Although a decrease in precipitation in the 1990s in the HWYR was reported by previous studies [31,32], the decrease is not significant, as there is only one change point (2002) detected by the moving t-test (Figure 7). However, precipitation intensity decreased by 8.36% in period 1988-1995 and increased by 4.49% in period 1996-2013.…”

“…Meanwhile, the significantly decreased precipitation intensity is also a crucial factor that resulted in an evaporation increase in the 1990s. The increase in precipitation after 2002 offset the effects of increased evaporation, and is the main reason leading to a recovery of the runoff in the recovery period (2003-2013) [31,32].…”

“…In this study, we ignored frozen ground degradation impacts on water balance in the HWYR and focused on its impacts on winter baseflow and snowmelt runoff. Nevertheless, the frozen ground degradation impacts have been considered in long-term water balance analyses lately [7,32,34]. Duan [7] used a sensitive-based method to analyze permafrost effects on runoff change of watersheds in north-eastern China and concluded that permafrost thaw increased runoff, but it is difficult to separate the permafrost degradation impacts from complex driving factors.…”

“…Compared to the pre-change period , the annual mean runoff of the headwater basins decreased by 20% in the 1990s, but demonstrated a recovery in the 21st century, especially in the sub-basin above Jimai station where runoff increased by 6.2% relative to the pre-change period [32]. The frozen ground degradation effects on the hydrological change have also drawn concern in this area recently, but have only been discussed at an annual scale [16,[32][33][34]. Although long-term annual runoff characteristic changes have been extensively discussed and investigated in previous studies, the long-term variations of runoff in different seasons are still unknown.…”

“…The long-term variations of annual runoff of the HWYR can be generally divided into three periods: a pre-change period ), a decrease period (the 1990s), and a recovery period (the 21st century) [30,31]. Compared to the pre-change period , the annual mean runoff of the headwater basins decreased by 20% in the 1990s, but demonstrated a recovery in the 21st century, especially in the sub-basin above Jimai station where runoff increased by 6.2% relative to the pre-change period [32]. The frozen ground degradation effects on the hydrological change have also drawn concern in this area recently, but have only been discussed at an annual scale [16,[32][33][34].…”