On May 29, 2024, Associate Professor Yang Yuting’s team from the Department of Hydraulic Engineering at Tsinghua University published a research article titled “Streamflow seasonality in a snow-dwindling world” in Nature. The study systematically revealed the complex mechanisms of river streamflow processes in response to changes in snowfall and clarified the patterns of how reduced winter snowfall affects the seasonality of streamflow.
Mountainous, plateau, and high-latitude cold regions are sensitive areas to climate change, with warming rates significantly higher than the global average. This has led to significant degradation of cryospheric elements, which strongly affects regional hydrological processes. Snow is an important component of the cryosphere, and the runoff generated from snowmelt provides essential freshwater resources for more than 1/6 of the world’s population. As global climate change intensifies, there is a clear decreasing trend in snow accumulation in cold regions, posing significant challenges to water resource management, food security, and the prevention of water-related disasters such as floods and droughts. However, there is still no global consensus on how reduced snowfall affects river streamflow processes, and research conclusions vary significantly across different regions.
Based on long-term (1950-2020) hydro-meteorological observation data from over 3,000 snow-affected basins in the Northern Hemisphere, the study found that reduced winter snowfall leads to earlier snowmelt in the spring and a delayed precipitation centroid timing. Due to differences in the sensitivity of streamflow timing to snowmelt and precipitation across different basins, in basins with a higher proportion of snowfall, reduced winter snowfall results in earlier streamflow. In contrast, reduced winter snowfall results in delayed streamflow in basins with a lower proportion of snowfall. The two opposite trends mentioned above are associated with a snowfall proportion threshold, which is an average long-term snowfall proportion of about 40%. This threshold corresponds to an average elevation of approximately 1,500 meters. The study also found that reduced snowfall leads to a significant decrease in warm-season runoff and annual runoff peaks, thereby reducing the seasonal variability of streamflow. At the same time, reduced snowfall increases the seasonal variability of streamflow and the interannual fluctuations in the timing of the streamflow centroid. This study systematically revealed the patterns of snowmelt runoff response under climate warming, challenging the traditional understanding of “reduced snowfall, earlier snowmelt, and earlier streamflow.” It provides new insights into the mechanisms by which reduced snowfall affects streamflow processes in the context of global warming.
Relationship between mean annual snowfall fraction and streamflow seasonality
Impacts of temporal changes in snowfall fraction on streamflow seasonality
The research findings also highlight the challenges faced by global and regional water resource management, which are of great significance for ensuring the sustainable use of water resources. Continued warming may lead to more frequent spring floods in areas with significant snow accumulation, while in regions with less snowfall, the frequency and intensity of spring floods may show a declining trend. At the same time, reduced winter snowfall will lead to decreased runoff in the summer and fall, increasing the risk of drought. This poses threats to water supply, food security, and hydropower production. Additionally, the increased interannual fluctuations in streamflow seasonality mean that seasonal streamflow forecasting becomes more difficult and uncertain. This will present greater challenges for the seasonal prediction and management of water resources. To address this, the authors of the paper emphasize the need to reassess the planning and management of water resource infrastructure in snow-affected regions. They advocate for the development of flexible and targeted strategies to adapt to the impacts of climate change on regional hydrological cycles, ensuring long-term water security and sustainable use.
HAN Juntai, a PhD student, and LIU Ziwei, a PhD graduate from the Department of Hydraulic Engineering at Tsinghua University, are the co-first authors of the paper, while Associate Professor YANG Yuting is the corresponding author. The paper’s collaborators include Professor WOODS Ross from the University of Bristol in the UK, Researcher Tim McVicar from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, Professor YANG Dawen from Tsinghua University, Assistant Researcher WANG Taihua, PhD student HOU Ying, and postdoctoral researchers GUO Yuhan and LI Changming. This research was supported by the National Natural Science Foundation of China’s Yellow River Special Project (42041004), the General Project (42071029), the Ministry of Science and Technology's Key R&D Project (2023YFC3206603), and the Key R&D Project of the Yunnan Provincial Department of Science and Technology (202203AA080010).
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