Research Background
Global warming is accelerating the degradation of permafrost in high-altitude cold regions and is also altering the way rivers receive water. The Qinghai-Tibet Plateau is the world’s largest and highest-altitude permafrost region, as well as an important source area for numerous rivers. As the active layer of permafrost deepens and seasonal freeze-thaw processes intensify, the connections among surface water, soil water, and groundwater are being reshaped, leading to changes in the sources of river runoff. Previous studies have shown that precipitation, snowmelt, soil water, and groundwater are the primary sources of replenishment for high-altitude cold rivers. However, during the alternating freeze-thaw cycle, how exactly do these water sources enter river channels? Which stage dominates the recharge process? And which layer of soil water contributes most significantly? These questions still lack clear quantitative understanding.
Recently, the research team led by Professor Li Xiaoyan from Beijing Normal University focused on the Bukha River Basin—the largest river flowing into Qinghai Lake—and used a combination of hydrogen and oxygen stable isotopes, hydrological and meteorological observations, and the MixSIAR mixing model to systematically analyze the changes in the sources and transport pathways of runoff in high-altitude cold-region rivers during freeze-thaw cycles. This study provides new evidence for understanding the response of water cycles in high-altitude cold-region watersheds under the backdrop of climate warming.
Figure 1. Figures (a), (b), and (c) respectively illustrate the locations of QTP and QLB, as well as the spatial distribution of sampling points within BRB and the distribution of permafrost.
Research Methodology
The study area is located in the Bukha River basin, the largest river flowing into Qinghai Lake. The research team established a systematic hydrological observation network, integrated hydrological and meteorological data collected in 2024, and sampled precipitation, river water, groundwater, and soil water from three depth layers (0–90 cm) between May and October 2025. By measuring the stable isotopes δ²H and δ¹⁸O and employing the MixSIAR Bayesian mixing model, the team quantitatively analyzed the contribution proportions of different water sources to river runoff.
The freeze-thaw period is defined based on daily-scale air temperature and ground temperature:
Melting period: Daily maximum air temperature and soil temperature > 0℃;
Melting period: Daily minimum air temperature and soil temperature > 0℃;
Freezing period: Daily minimum air temperature and soil temperature < 0℃;
Prior to conducting soil water isotope analysis, the research team employed the LI-2100 Automated Vacuum Water Extraction System (Beijing Lijia United Technology Ltd.) to extract water from the soil samples. Based on the principle of low-temperature vacuum distillation, this system enables efficient extraction of soil water under sealed and stable conditions, effectively minimizing the impact of evaporation and fractionation during the extraction process on the δ²H and δ¹⁸O measurement results, thereby providing a reliable sample basis for subsequent runoff source apportionment and water movement pathway identification.
Figure 2. Proportion of runoff sources in BRB (a, b: melting; c, d: melting; e, f: freezing)
Figure 3. Contribution of rainfall and snowmelt water to soil moisture during the freezing–thawing and thawing periods in the BRB region (Upper plot: freezing–thawing period; Lower plot: thawing period).
Figure 4. Conceptual diagram of runoff recharge during the freeze–thaw process
Research results
Rainfall is the primary source of soil water, while snowmelt is the secondary source.
Deep soil water is an important source of recharge for runoff in cold and high-altitude rivers;
The freeze-thaw process promotes the exchange between surface water and groundwater, and groundwater recharge reaches its peak during the freezing period.
There are differences between the permafrost zone upstream and the seasonal frost zone downstream.
The freeze-thaw process not only alters the amount of water but also reshapes the pathways through which water enters rivers.
Conclusion
The freeze-thaw process is not simply a matter of thawing the water trapped in frozen soils; rather, it continuously alters the sources, connectivity, and flow paths of water within high-altitude cold-region watersheds. This study shows that as the active layer thaws deeper, the role of deep soil water and groundwater in river recharge becomes increasingly prominent—especially during the freezing season, when groundwater emerges as a critical source for sustaining baseflow in rivers. This finding underscores that, against the backdrop of climate warming, understanding changes in river runoff on the Qinghai-Tibet Plateau cannot focus solely on precipitation and snowmelt; instead, we must integrate the freeze-thaw process, deep soil water, and surface water-groundwater interactions into a comprehensive hydrological framework. In the future, combining long-term fixed-site observations, isotopic tracing, and hydrological modeling will help us more accurately predict changes in water resources and their ecological impacts in high-altitude cold-region watersheds.
Journal of Publication: Catena [Impact Factor: 5.7]
Research Institution: Beijing Normal University
Study site: Buhu River Basin, Qinghai Lake
Equipment used: LI-2100 Automated Vacuum Water Extraction System
DOI: https://doi.org/10.1016/j.catena.2026.110230