Midpoint characterization factors to assess impacts of turbine water use from hydropower production.

Purpose: Life cycle assessment (LCA) distinguishes three types of water use: (1) consumptive water use, (2) degradative water use, and (3) in-stream water use. When it comes to assessing the impact of turbine water use (TWU, major source of in-stream water use) in LCA, so far, no method exists to quantify the related environmental impacts. Here, we developed the first midpoint characterization factors (CFs) with global coverage for turbine water use of storage and pumped storage hydropower power plants. Methods: The midpoint CF at the basin scale describes the hydropower regulation potential (HRP) [HDOR·y] per TWU [m³]. The HRP indicates the probability of how strongly the natural flow regime of a river is potentially affected by all upstream reservoir operation, calculated as the quotient between reservoir volume [m³] and the annual river discharge [m³/y]. The hydropower degree of regulation (HDOR) thereby equals the unitless m³/m³ fraction. The TWU depends on the electricity production [kWh] and the turbine efficiency [m³/kWh]. We tested the sensitivity of the input data on the calculated CFs for four parameters (discharge, turbine efficiency, multipurpose allocation, and plant type). Furthermore, we performed a case study to analyze if consumptive and TWU impacts of producing 1 kWh are correlated or not. Results and discussion: The calculated CFs for the 342 basins vary from 1.13E-13 HDOR·y/m³ to 3.28E10-7 HDOR·y/m³. The HDOR values range from 0.0015 to 16.66, and the TWU varies between 0.0030 km³ and 2824 km³. A HDOR ≥ 0.02 can be interpreted as affected basin, and only 23 out of 342 basins have a HDOR below this threshold. This confirms that TWU of hydropower production can have important environmental impacts. The sensitivity analyses revealed that discharge and turbine efficiency are the most sensitive parameters because they are influencing almost all basins. The results of the case study showed that a high consumptive water-use impact does not automatically lead to a high TWU impact and vice versa (R² values of 0.0081 and 0.003). Conclusion: Our study highlights that it is important to account for the environmental impacts of in-stream water use in LCA, as otherwise, the environmental impact can be underestimated, which could lead to wrong conclusions. However, the CFs are not meant to replace a local risk assessment of hydropower reservoir operation and should only be used for relative comparison between basins. The CF application in LCA will represent a step forward towards more sustainable hydropower development. [ABSTRACT FROM AUTHOR]