Understanding Trade-Offs Among Ecosystem Services of Multiple Dams in the Upper Cauvery Basin: A Hydro-Economic Analysis Using a Landscape-Based Hydrological Model"

Dam construction poses a significant threat to the health of watershed ecosystems by altering natural hydrological regimes. This study assesses the impact of multiple dams on hydrological flow patterns and aquatic ecosystems in the Upper Cauvery River Basin, India. It focuses on the trade-offs between economic benefits and ecological services resulting from modified flow regimes. This study uses a previously developed integrated model that combines a landscape-based hydrological framework with a reservoir operations model at the basin scale to provide new insights into the daily-scale alterations of ecosystem services. This approach is flexible to simulate changes in flow regimes due to the synthetic placement of reservoirs at any location within the river network. As a proof of concept, the study evaluates economic and ecological consequences that may arise from alternative spatial configurations of existing reservoirs in the Upper Cauvery Basin.  Further, the hydrological impacts of reservoir configurations are quantified using Indicators of Hydrologic Alteration (IHA). Two critical ecosystem services dependent on river flow regimes—irrigated agricultural production and fish biodiversity, represented by a normalized fish diversity index—are evaluated. A trade-off curve, or production possibility frontier, illustrates the relationship between these services. The findings indicate that smaller reservoirs located on lower-order streams are more favourable for balancing economic and environmental outcomes than larger reservoirs. Additionally, irrigating higher-value crops can maximize the economic return from stored water and result in similar economic benefits with lower storage needs and less hydrological disruption. This approach allows water and river basin managers to assess the provision of ecosystem services in hydrologically altered basins, optimize operations of reservoirs, and make decisions on removing dams where feasible and necessary, leading to a more balanced approach towards managing ecosystem services.