Alteration of River Flow and Flood Dynamics by Existing and Planned Hydropower Dams in the Amazon River Basin

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.

Increased floodplain inundation in the Amazon since 1980

“…Understanding how these changes may interact either synergistically or antagonistically is important for planning dams and navigation channels as well as regulating deforestation. Furthermore, although our estimates based on hydrologic-hydrodynamic modeling considered a natural basin scenario, without the effects of anthropogenic impacts such as dams (Chaudhari andPokhrel 2022, Flecker et al 2022), the impacts of rainfall changes on inundation extent reported here are well aligned with evidence from other, rainfallindependent remote sensing datasets. It is important to stress that such models have simplifications such as time-constant and rectangular river channel cross sections, which are necessary to be assumed due to scarcity of detailed, in situ data to be used in parameterization.…”

“…If sustained in the future, the increase in maximum inundation extent observed across the central Amazon floodplains, driven by a change in rainfall regime, is unlikely to be the only change affecting floodplain inundation regimes. Human-driven hydrological changes in the basin that potentially affect river discharge and floodplain inundation include construction of hydropower dams (Chaudhari and Pokhrel 2022), the development of industrial waterways in the western Amazon tributaries that require dredging of river channels (AIDESEP 2019), and deforestation in both the uplands and floodplains (Castello et al 2013). Understanding how these changes may interact either synergistically or antagonistically is important for planning dams and navigation channels as well as regulating deforestation.…”

“…The Amazon River system is increasingly affected by multiple stressors (Castello et al 2013). Changes in regional climate have been superimposed on human disturbances such as construction of dams (Chaudhari and Pokhrel 2022) and deforestation in both uplands (Costa et al 2003) and floodplains (Renó et al 2011). Based on river gage measurements, recent studies have shown higher maximum water levels in the Amazon since the late 1990s (Gloor et al 2013, Barichivich et al 2018), linked to a ∼17% increase in wet-season rainfall over the northern part of the basin (north of 5 • S) from 1981 to 2017 (Espinoza et al 2019a, Haghtalab et al 2020, Funatsu et al 2021.…”

Flood risk assessment for Indian sub-continental river basins

“…The CaMa-Flood model combined with the H08 model has been used for several river basins globally (Boulange et al, 2021; C. M. R. Mateo et al, 2013). The CaMa-Flood model performs well in simulating flood dynamics (Chaudhari and Pokhrel, 2022;H. Dang et al, 2022;Gaur & Gaur, 2018;Hirabayashi et al, 2013Hirabayashi et al, , 2021Yamazaki et al, 2018;Yang et al, 2019).…”

Identifying the current and future status of freshwater connectivity corridors in the Amazon Basin

“…Dams present are not only unpassable obstacles for migratory species but also affect the hydrological dynamics and water quality characteristics that can potentially affect a wide range of freshwater organisms (Poff & Zimmerman, 2010). The most significant cumulative hydrological alterations of dams in the Amazon are in the frequency and duration of flow pulses (Timpe & Kaplan, 2017), with large dams in certain subbasins of the Amazon having already altered downstream river flow amplitude by up to 3 orders of magnitude (Chaudhari & Pokhrel, 2022). However, the Amazon still contains many free‐flowing rivers (FFR) with a recent study documenting the Amazon River as the longest remaining FFR from source to outlet globally (Grill et al, 2019).…”