Climate change–hydropower reliability framework: linking climate, river flow and energy security in the Punatsangchu and Wangchu River Basins, Bhutan

Abstract

Bhutan’s hydropower sector is an important contributor to the country’s energy supply and economy. However, climate change is expected to alter temperature, rainfall patterns, and river flows, potentially affecting seasonal water availability and hydropower reliability. This study synthesizes existing evidence to develop a simple climate–hydropower reliability framework for Bhutan. Observed climate evidence from the Climate Atlas of Bhutan (1996–2025), projected climate and river-flow findings from the CMIP6 assessment, documented extreme-weather impacts, and hydropower-related concepts from the Power System Master Plan 2040 are reviewed and compared for the Punatshangchu River Basin (PRB) and Wangchu River Basin (WRB). The assessment indicates contrasting basin responses. The PRB shows increasing flows across the near-, mid-, and long-term periods, with stronger monsoon peaks and increasing risks of flooding, sediment transport, and infrastructure stress. In contrast, the WRB shows declining or stagnant flows in the near- and mid-term periods, raising concerns over dry-season water availability. These findings demonstrate the importance of basin-level climate-risk assessment. The study concludes that hydropower reliability depends not only on annual water availability but also on the timing, variability, and extremes of river flow. The proposed framework links observed and projected climate conditions, hydrology, extreme events, seasonal water availability, and hydropower reliability to support basin-specific and climate-informed hydropower planning in Bhutan.