The Waters That Do Not Reach the River: Stable Precipitation, Rising Evapotranspiration, and the Flow Decline in Brahmani–Baitarani River Basin, Eastern India

The Brahmani–Baitarani River Basin (BBRB), a critical water resource for agriculture and industry in eastern India, has experienced a paradoxical decline in river flow over the past two decades despite stable or increasing precipitation. This study investigates long‐term precipitation trends (1981–2022) and their hydrological implications using the Mann–Kendall test, Sen's slope estimator, and standardized precipitation index (SPI). Results indicate an overall positive trend of 3.68 mm/year in precipitation. Subperiod analyses (1981–2000 and 2001–2022) show slight negative and positive tendencies, respectively, though neither was statistically significant. Further, the SPI revealed improved precipitation distribution between the two periods, particularly during the monsoon months, suggesting stable or enhanced precipitation levels. However, river flow data from Central Water Commission stations at Jenapur and Anandapur show consistent declines (−8.1 and −1.1 m 3 /s per year, respectively), uncorrelated with precipitation trends. Multiple linear regression (MLR) analysis incorporating climatic and ecological variables identifies rising evapotranspiration (ET) and vegetation density (NDVI) as dominant drivers of reduced water availability. Increased vegetation growth, while ecologically beneficial, enhances transpiration losses, creating a climate–vegetation feedback loop that exacerbates water stress. TerraClimate and MODIS data confirm rising ET trends (2001–2022), aligning with NDVI increases, suggesting that greening landscapes counteract precipitation gains. These findings challenge conventional rainfall–runoff assumptions, highlighting the underestimated role of ecological processes in hydrological systems. The study underscores the need for integrated water management strategies that balance afforestation benefits with hydrological trade‐offs. Policymakers must address anthropogenic pressures while promoting low–water‐use vegetation and sustainable land practices. By linking climate dynamics, vegetation changes, and river flow decline, this research provides a framework for reconciling agricultural productivity, ecological resilience, and water security in monsoon‐dependent basins. The outcomes advocate for adaptive policies aligned with Sustainable Development Goals (SDGs) to mitigate escalating water crises in regions facing similar climatic and developmental challenges.