Distinguishing streamflow trends caused by changes in climate, forest cover, and permafrost in a large watershed in northeastern China

Abstract

Understanding how rivers respond to changes in land cover, climate, and subsurface conditions is critical for sustainably managing water resources and ecosystems. In this study, long-term hydrologic, climate, and satellite data from the Upper Tahe River watershed (2359 km 2 ) in the Da Hinggan Mountains of northeast China were analysed to quantify the relative hydrologic effects of climate variability (system input) and the combined influences of forest cover change and permafrost thaw (system characteristics) on average annual streamflow (system response) using 2 methods: the sensitivity-based method and the Kendall-Theil robust line method. The study period was subdivided into a forest harvesting period (1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987), a forest stability period (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), and a forest recovery period (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012). The results indicated that the combined effects of forest harvesting and permafrost thaw on streamflow (+ 47.0 mm) from the forest harvesting period to the forest stability period was approximately twice as large as the effect associated with climate variability (+20.2 mm). Similarly, from the forest stability period to the forest recovery period, the decrease in average annual streamflow attributed to the combined effects of forest recovery and permafrost thaw (−38.0 mm) was much greater than the decrease due to climate variability (−22.2 mm). A simple method was used to separate the distinct impacts of forest cover change and permafrost thaw, but distinguishing these influences is difficult due to changes in surface and subsurface hydrologic connectivity associated with permafrost thaw. The results highlight the need to consider multiple streamflow drivers in future watershed and aquatic ecosystem management. Due to the ecological and hydrological susceptibility to disturbances in the Da Hinggan Mountains, forest harvesting will likely negatively impact ecohydrological processes in this region, and the effects of forest species transition in the forest recovery process should be further investigated.

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

“…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.…”

“…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. Based on a modified decomposition method, Wu [32] also found that the permafrost degradation presented a positive effect, which is contrary to temperature impacts on runoff change in the headwaters of the Yellow River (HWYR).…”

“…[1][2][3][4][5]. Climate change impacts the hydrological change of cold regions, both directly through changes in climate forcing (precipitation and evaporation) and indirectly through changes in runoff generation caused by the degrading cryosphere, which has increased the uncertainties and complexities of hydrological studies in cold regions [6,7].…”

Quantifying Impacts of Forest Recovery on Water Yield in Two Large Watersheds in the Cold Region of Northeast China

“…Annual forest cover data from 1987 to 2016 were obtained from the forest resource inventory database administrated by the Xinlin Forestry and Yichun Forestry Bureaus [8,27], respectively. Following the protocol of "Observation Methodology for Long-term Forest Ecosystem Research" of the National Standards of the People's Republic of China (GB/T 33027-2016), the forest coverage was calculated as percent ratio of all forest area with canopy coverage greater than 30% over the total area of the study watershed.…”

“…For example, Qiu [3] reported that reforestation may potentially contribute to the droughts in Southwest China. Although numerous existing studies were dedicated to assessing the impacts of reforestation on water yield globally with varying numbers of watersheds and watershed sizes, as reviewed by Zhang et al [4] and Li et al [5], there exists limited studies [6,7] examining the effects of afforestation and reforestation on water yield in boreal regions, and, particularly, a lack of studies in the boreal forest region in China [8]. This raises a critical need to study such effects in the boreal regions to enrich our knowledge of the relationship between forest recovery and water resources.…”