Future low flow, ecological flow, and drought patterns in a transboundary basin under bias-corrected CMIP6 projections

Graphical abstract summarizing the methodological workflow of the study. The Brahmaputra River Basin (BRB) is expected to experience marked impacts, with climate change likely to alter low-flow conditions, ecological flows, water availability, and drought dynamics. This study applies the SWAT hydrological model to assess potential changes in low flows, ecological flow thresholds, and drought frequency using the Streamflow Drought Index (SDI) under CMIP6 climate scenarios. Low flow exhibits a declining trend for the far future and an increasing trend for the near future, with a 100-year return period. Under SSP3-7.0 in the near future, flows may increase by up to 13% (uncertainty range: 10 to 28%), whereas far-future ensemble projections indicate a potential decline of 8% (uncertainty range: −58 to 11%), which reflects significant inter-model spread. Standardized Discharge Index (SDI) analysis reveals more frequent wet and dry extremes than in the historical baseline, particularly in the far future. Additionally, Ecological flows exhibit a declining trend across all scenarios, with reductions of approximately 2.3% (range: −4.4 to −2.3%) under SSP3-7.0 in the near future. These findings highlight the need for adaptive water management strategies that address both hydrological extremes and the inherent uncertainties of future climate projections.