Global freshwater discharge is essential for human development, influencing hydrological and water cycles and biogeochemical processes. The Red River system, a vital transboundary river, is driven by climate and regulated by dam construction and changes in land use and land cover (LULC). This study aims to quantitatively separate effects of human activities on discharge alterations from climate variability. We combined linear regression and double mass curve to estimate human contributions, in conjunction with Mann-Kendall, Pettitt, and Sen’s slope methods for trend analysis. The analyses were performed on daily discharge data from four stations (Hoa Binh, Vu Quang, Yen Bai, Ha Noi) from the 1950s to 2023, along with CHIRPS rainfall (1981–2023) and MODIS NDVI (2002–2023). Our findings reveal complex long-term trends: flood-season and maximum discharges generally decreased significantly across most months and locations (e.g., August at Hoa Binh: −61.4 m³/s/yr). Conversely, dry-season discharge at Hoa Binh and Vu Quang increased substantially, whereas at Yen Bai it decreased in all dry-season months. Flood season, maximum, and annual mean rainfalls remained statistically stable. This stability in rainfall, despite profound changes in discharge, indicates the increasingly dominant role of human activities in controlling the flow regime, surpassing climate variability. Hydropower dams are identified as the primary drivers of flood-season discharge decreases and dry-season discharge increases at Hoa Binh, Vu Quang, and Ha Noi. Quantitatively, human activities reduced the flood-season discharge by up to − 55.6% and increased the dry-season discharge by up to 67.7% at the Hoa Binh hydrological station, where the human effect was strongest.
Nam et al. (Wed,) studied this question.