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The identification and accurate quantification of sources or sinks of greenhouse gas (GHG) have become a key challenge for scientists and policymakers working on climate change. The creation of a hydropower reservoir, while damming a river for power generation, converts the terrestrial ecosystems into aquatic and subsequently aerobic and anaerobic decomposition of flooded terrestrial soil organic matter resulting in the emission of significant quantity of GHG to the atmosphere. Tropical/subtropical hydropower reservoirs are more significant sources of GHG compared to boreal or temperate one. This paper aims to estimate the emission factor (gCO2eq./kWh) and net GHG emission from Koteshwar hydropower reservoir in Uttarakhand, India. Further, estimated GHG are compared with those from global reservoirs located in the same eco-region so that its impact could be timely minimized/mitigated. Results have shown that emission factor and net GHG emission of Koteshwar reservoir are, respectively, estimated as 13.87 gCO2eq./kWh and 167.70 Gg C year−1 which are less than other global reservoirs located in the same eco-region. This information could be helpful for the hydropower industries to construct reservoirs in tropical eco-regions. [ABSTRACT FROM AUTHOR]

Hydropower is one of the widely used renewable energy sources and contributing a huge share in overall electricity generation in developing countries like India. A few decades ago, hydropower reservoirs were found to be a clean source of renewable energy, but after the pre-industrial era (1990s), these reservoirs were emitting a significant amount of greenhouse gases (GHG). The GHG are contributing a huge share to the regional/global carbon budget. The current study represents the first regional review and focuses on: present scenarios of Indian hydropower, environmental issues, constraints in dam construction, identified key predictors (i.e., age, depth of reservoir) impacting GHG potential, GHG risk to reservoirs, and suggested mitigation measures to the way forward for the sustainable planning of hydropower development. The review reveals that most Indian hydropower reservoirs are coming under the low to medium GHG risk of reservoirs. Small hydropower projects (SHPs) are deliberated as a worthy alternative for the sustainable management of hydropower projects. There are still many issues associated with SHPs, which cannot be neglected completely. This study provides baseline information to the hydropower industries, policy-makers, environmentalists, and water managers to take corrective measures before impoundment of a reservoir at the regional and global scale. [Display omitted] • This is the first review summarises GHG emission from Indian Hydropower. • Indian hydropower are coming under the low to medium GHG risk of reservoirs. • Small hydro is deliberated as a worthy alternative for the sustainable management of hydropower projects. • Research is urgently needed in tropical eco-regions to know the GHG risk to reservoirs. • Proposed mitigation strategies for carbon deduction in future dam constructions. [ABSTRACT FROM AUTHOR]