Review on the externalities of hydropower: A comparison between large and small hydropower projects in Tibet based on the CO2 equivalent

Abstract

Both large hydropower projects (LHPs) and small hydropower projects (SHPs) have environmental and societal externalities, which have not been taken into account in their construction costs and operation benefits. These externalities are becoming an increasingly important issue in hydropower development policy making; as a result, it is essential to perform a systematic assessment of them among different hydropower patterns.The purpose of this paper was to establish a general externalities inventory for hydropower development through reviewing worldwide. This inventory allowed these externalities to be classified into three categories: externalities due to civil works, due to reservoir impoundment and due to cumulative impacts. Meanwhile, as these inventories were all related to greenhouse gas (GHG) activity, they could be transformed into the CO2 equivalent (CO2-e), either directly or indirectly. This transformation method not only enables a feasible comparison of the externalities between different hydropower patterns but also enriches the carbon footprint assessment for hydropower.In the case study of 5 LHPs (>50MW) and 10 SHPs in Tibet, China, SHPs have reduced externalities compared to LHPs, with SHPs and LHPs representing a burden of 5.1 and 29.2gCO2-ekWh−1 on average, respectively. This extra carbon emission burden indicates that the present low-carbon potential of hydropower has been overestimated. Meanwhile, this reduced externality makes SHPs perform better in terms of environmentally friendly development and low-carbon energy than LHPs for Tibet. The externality caused by reservoir impoundment and occupation is the primary component of the total externality of a LHP; therefore, increasing the power density is an efficient way to decrease its externality.