An official website of the United States government
Abstract Hydropower dams have received increased global attention due to their detrimental socioenvironmental ramifications. Such attention has led to an increase in studies on the impacts of reservoir operation on river flow; however, a holistic understanding of the compounded effects of hydropower dams on different hydrological characteristics is lacking, especially for large river basins such as the Amazon where hydropower development is on the rise. Here, we mechanistically quantify the historical impacts of existing dams and the potential impacts of the collective operation of existing and planned dams on a basin‐wide scale in the Amazon for the 1981–2019 period. We build on the recently developed high‐resolution (3‐arcmin; ∼5 km) river‐floodplain‐reservoir model, the CaMa‐Flood‐Dam, which is enhanced to realistically simulate hydropower dam operation considering maximized power production. Flood simulations are further downscaled to 3 arc‐seconds (∼90 m) resolution to investigate the impacts of dams on fine‐scale flood dynamics across the basin. Results indicate that existing dams have substantially altered downstream river flow and flooding patterns across the Amazon River basin. Specifically, large dams in the Amazonian subbasins, including the Xingu, Madeira, and Tocantins, have altered downstream river flow amplitude by up to 3 orders of magnitude. Further, the collective operation of existing and planned dams could increasingly alter river flow patterns, causing ∼10% decrease in flood duration in many parts of the Amazon mainstem. Our results provide quantitative evidence on the severity of the hydrologic impacts of large hydropower dams and have important implications for sustainable hydropower operation and development in the Amazon and worldwide.
more »
« less
High Resolution Modeling of River‐Floodplain‐Reservoir Inundation Dynamics in the Mekong River Basin
Abstract Numerous studies have examined the changes in streamflow in the Mekong River Basin (MRB) using observations and hydrological modeling; however, there is a lack of integrated modeling studies that explicitly simulate the natural and human‐induced changes in flood dynamics over the entire basin. Here we simulate the river‐floodplain‐reservoir inundation dynamics over the MRB for 1979–2016 period using a newly integrated, high‐resolution (~5 km) river hydrodynamics‐reservoir operation model. The framework is based on the river‐floodplain hydrodynamic model CaMa‐Flood in which a new reservoir operation scheme is incorporated by including 86 existing MRB dams. The simulated flood extent is downscaled to a higher resolution (~90 m) to investigate fine‐scale inundation dynamics, and results are validated with ground‐ and satellite‐based observations. It is found that the historical variations in surface water storage have been governed primarily by climate variability; the impacts of dams on river‐floodplain hydrodynamics were marginal until 2009. However, results indicate that the dam impacts increased noticeably in 2010 when the basin‐wide storage capacity doubled due to the construction of new mega dams. Further, results suggest that the future flood dynamics in the MRB would be considerably different than in the past even without climate change and additional dams. However, it is also found that the impacts of dams can largely vary depending on reservoir operation strategies. This study is expected to provide the basis for high‐resolution river‐floodplain‐reservoir modeling for a holistic assessment of the impacts of dams and climate change on the floodpulse‐dependent hydro‐ecological systems in the MRB and other global regions.
more »
« less
- Award ID(s):
- 1752729
- PAR ID:
- 10374499
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 56
- Issue:
- 5
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. Flow regimes in major global river systems are undergoing rapid alterations due to unprecedented stress from climate change and human activities. The Mekong River basin (MRB) was, until recently, among the last major global rivers relatively unaltered by humans, but this has been changing alarmingly in the last decade due to booming dam construction. Numerous studies have examined the MRB's flood pulse and its alterations in recent years. However, a mechanistic quantification at the basin scale attributing these changes to either climatic or human drivers is lacking. Here, we present the first results of the basin-wide changes in natural hydrological regimes in the MRB over the past 8 decades and the impacts of dams in recent decades by examining 83 years (1940–2022) of river regime characteristics simulated by a river–floodplain hydrodynamic model that includes 126 major dams in the MRB. Results indicate that, while the Mekong River's flow has shown substantial decadal trends and variabilities, the operation of dams in recent years has been causing a fundamental shift in the seasonal volume and timing of river flow and extreme hydrological conditions. Even though the dam-induced impacts have been small so far and most pronounced in areas directly downstream of major dams, dams are intensifying the natural variations in the Mekong's mainstream wet-season flow. Further, the additional 65 dams commissioned since 2010 have exacerbated drought conditions by substantially delaying the MRB's wet-season onset, especially in recent years (e.g., 2019 and 2020), when the natural wet-season durations are already shorter than in normal years. Further, dams have shifted by up to 20 % of the mainstream annual volume between the dry and wet seasons in recent years. While this has a minimal impact on the MRB's annual flow volume, the flood occurrence in many major areas of Tonlé Sap and the Mekong Delta has been largely altered. This study provides critical insights into the long-term hydrological variabilities and impacts of dams on the Mekong River's flow regimes, which can help improve water resource management in light of intensifying hydrological extremes.more » « less
-
Abstract Manmade reservoirs are important components of the terrestrial water balance. Thus, considering the hydro‐climatic effects of reservoirs is important in water cycle studies at a river basin to global scales; yet, reservoirs are represented poorly in large‐scale hydrological and climate models. Here we present a high‐resolution (5 km) continental‐scale reservoir storage dynamics and release scheme by enhancing existing schemes and adding critical novel parameterizations to improve reservoir storage and release simulations. The new scheme simulates river‐floodplain‐reservoir storages in an integrated manner considering their spatial and temporal variations. A new calibration scheme is also incorporated to better simulate reservoir dynamics considering cascade‐reservoir effects. Further, since no reservoir bathymetry data are available over large domains, we use a state‐of‐the‐art digital elevation model and reservoir extent data to derive reservoir bed elevation. The new scheme is integrated within the river‐floodplain routing scheme of a continental hydrological model LEAF‐Hydro‐Flood. Results from the simulation of ~1,900 reservoirs within the contiguous United States suggest that the model well captures the observed reservoir storage‐release dynamics. Comparison of our results with those from the existing schemes suggest a significant improvement; importantly, the new scheme reduces the excessive and frequent reservoir overfilling and underfilling. Comparison of results with satellite‐based surface water data shows that the model accurately reproduces the large‐scale patterns of reservoir‐floodplain inundation extents. It is expected that the results of this study will inform the incorporation of reservoirs in hyper‐resolution models to improve simulations of terrestrial water storage and flow and examine reservoir‐atmosphere interactions over large domains.more » « less
-
Abstract The Mekong River Basin (MRB) is undergoing unprecedented changes due to the recent acceleration in large-scale dam construction. While the hydrology of the MRB is well understood and the effects of some of the existing dams have been studied, the potential effects of the planned dams on flood pulse dynamics over the entire Lower Mekong remains unexamined. Here, using hydrodynamic model simulations, we show that the effects of flow regulation on downstream river-floodplain dynamics are relatively predictable along the mainstream Mekong, but flow regulations could potentially disrupt the flood dynamics in the Tonle Sap River (TSR) and small distributaries in the Mekong Delta. Results suggest that TSR flow reversal could cease if the Mekong flood pulse is dampened by 50% and delayed by one-month. While flood occurrence in the vicinity of the Tonle Sap Lake and middle reach of the delta could increase due to enhanced low flow, it could decrease by up to five months in other areas due to dampened high flow, particularly during dry years. Further, areas flooded for less than five months and over six months are likely to be impacted significantly by flow regulations, but those flooded for 5–6 months could be impacted the least.more » « less
-
Abstract Floodplains provide essential ecosystem functions, yet >80% of European and North American floodplains are substantially modified. Despite floodplain changes over the past century, comprehensive, long-term land use change data within large river basin floodplains are limited. Long-term land use data can be used to quantify floodplain functions and provide spatially explicit information for management, restoration, and flood-risk mitigation. We present a comprehensive dataset quantifying floodplain land use change along the 3.3 million km2Mississippi River Basin (MRB) covering 60 years (1941–2000) at 250-m resolution. We developed four unique products as part of this work, a(n): (i) Google Earth Engine interactive map visualization interface, (ii) Python code that runs in any internet browser, (iii) online tutorial with visualizations facilitating classroom code application, and (iv) instructional video demonstrating code application and database reproduction. Our data show that MRB’s natural floodplain ecosystems have been substantially altered to agricultural and developed land uses. These products will support MRB resilience and sustainability goals by advancing data-driven decision making on floodplain restoration, buyout, and conservation scenarios.more » « less
