Hydropower dams have received increased global attention due to their detrimental socioenvironmental ramifications, resulting in increased concerns as to whether their energy benefits can outweigh the detrimental consequences. To fulfill rising energy demands driven by rapid population growth, especially in the developing world, hydropower has often been developed with a primary focus on energy generation. The re-emergence of large dams could very well bring large energy and economic incentives especially to the developing economies, however, these incentives may come at the expense of altering the natural flow regime of rivers with additional repercussions on the biodiversity and ecological productivity within the basins. With the continued interest in hydropower development, it is imperative to examine and understand the intricate changes to the basin's hydrology due to dam operations and further rethink hydropower design to avoid potentially catastrophic consequences. To date, several studies have simulated and examined the impacts of reservoir operation on the hydrological characteristics of global rivers. Although, these studies have made great strides in examining the impact of dams on river flow, the observation-based studies alone are not sufficient to disentangle the major drivers of change and there are major deficiencies in simulation-based studies in providing a comprehensive picture of the large-scale and cumulative impacts of dams. Hence, the actual impacts of the existing dams and the potential effects of new dams remain poorly understood. The overarching goal of this dissertation is to address this important research gap by employing a mechanistic approach to develop a holistic understanding of the hydrology of global river basins under the effects of climate change and human interventions, such as LULC change and dam operations. The study is conducted over the Amazon River basin that is increasingly dammed with hundreds of dams planned for the near future. The historical interannual and interdecadal hydrological changes in the Amazon River basin and its sub-basins are first investigated by implementing a high-resolution, physically based, continental-scale hydrological model, LEAF-Hydro-Flood (LHF), to determine the dominant mechanisms that modulate terrestrial water storage (TWS). The historical impacts of existing dams and the potential impacts from collective operation of existing and planned dams on a basin-wide scale in the Amazon are then quantified under the historical climate using a new dam operation scheme in a high-resolution hydrodynamic model, CaMa-Flood-Dam (CMFD). Using this new dam operation scheme, the potential future changes to the hydrology of the Amazon River basin are then quantified under cumulative operation of existing and planned dams and multiple climate change scenarios for the entire twenty first century. Lastly, this dissertation explores viable alternatives for hydropower generation, by assessing the feasibility-with respect to energy potential and cost-of implementing in-stream turbines to harness a large portion of the power that is expected to be generated by building large dams. The results from the aforementioned analysis provide major advances and crucial insights on the understanding of the integrated river-floodplain-reservoir dynamics in a flood and hydropower dominant river system, such as the Amazon, with further implications for sustainable hydropower development. Over the long run, this assessment could prove beneficial in investigating the future of hydropower in the Amazon and other regions worldwide (for example, the Mekong and Congo River basins) where a boom in construction of mega-scale hydropower dams is underway.
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