How cumulative impact assessment for Himalayan hydropower evolved from project EIAs to basin-scale studies, how climate change is exposing key gaps, and how to make it a true and useful planning tool.
The Himalaya is the focus of one of the world’s largest hydropower build-outs, with hundreds of projects planned or operating across India, Nepal, Bhutan and Pakistan, often in cascades on the same rivers. For decades these were assessed one at a time, through project-level EIAs that rarely looked beyond the dam site. This presentation traces how cumulative impact assessment (CIA) has evolved in response. It follows the shift from site-specific assessment to basin-scale studies, including carrying-capacity and cumulative impact studies for the Teesta, Alaknanda–Bhagirathi and Siang basins, and lender-driven approaches such as IFC’s CIA of Nepal’s Trishuli basin and the World Bank-funded comprehensive CIA for India’s Beas River Basin. It then examines how climate change-driven disasters (the 2013 Kedarnath floods, 2021 Chamoli debris flow, 2023 glacial lake outburst that destroyed the Teesta III dam, and 2026 Langtang Lirung Glacier collapse on the Nepal–Tibet border) exposed what conventional CIA has not captured well to date: the combination of compounding climate and geohazard risk, sediment dynamics, loss of free-flowing reaches and transboundary effects. Through comparative case studies, it assesses what has improved (basin-scale framing, valued-component approaches, lender standards) and what remains weak (baseline data, links to licensing decisions, enforcement and cross-border coordination). It closes with practical recommendations for making CIA a forward-looking planning tool rather than a compliance exercise, relevant to mountain river basins worldwide.
Michael D. Smith, Ph.D. is a Senior Vice President and National Practice Director for Environmental Policy, Process, and Assessment in the U.S. for WSP whose practice focuses on ESIA and CIA.