In a changing climate with variable and extreme precipitation patterns, increasing demand for energy and reduced storage capacity due to sedimentation, is it now timely to ask: ‘Has hydropower made the developing world more flood prone?’
As the objective of hydropower often competes with flood control, we need to critically study the complex relationship between hydropower development and downstream flood risk.
Indeed, we call for a paradigm shift in hydropower planning and management, emphasising the integration of adaptive flood risk mitigation into energy production strategies while also adapting to anticipated changes in climate and land cover with a robust sedimentation management strategy during the dam’s service lifespan.
Hydropower dams work on the concept of holding water behind at an elevation to maximise potential energy difference between upstream and downstream locations, which then maximises the electrical energy that can be generated. By virtue of a hydropower dam’s tendency to keep reservoirs almost full, residence time of surface water increases, leading to higher sedimentation, thermal stratification, less oxygenation of water and more methane emissions. However, one key societal function of dams that hydropower operations directly compete against is flood mitigation or flood control. While dams and the reservoirs behind them are usually engineered to control the river flow and mitigate downstream flood risks, paradoxically, these dams can exacerbate downstream flood hazards during hydropower operations. This is more likely in regions that are mountainous with high precipitation, where precipitation driven runoffs can lead to sudden and unexpected high inflows into reservoirs designed to be kept full to maximize energy production.
Consequently, an unprepared hydropower reservoir lacking the necessary flood cushion to store this unexpected high inflow can often be forced to pass all the inflow downstream just as suddenly, catching the downstream inhabitants unprepared.
Approximately 90% flood-prone, high precipitation and mountainous regions lie in the developing regions of the world, such as South and Southeast Asian, Central and South American, and West African countries. These regions have been experiencing rapid growth in hydropower over the past few decades.
In recent years we note an alarming trend of many flooding events that have been reported where the failure to adjust reservoir levels in a timely manner was considered a root cause (Kundu & Mothikumar, 1995; Zhang et al., 2014).
The alarming trends
A classic example is the 2018 floods in Kerala, India, which caused damages in excess of five billion US dollars (Pramanick et al., 2022). The flooding was primarily attributed to intense rainfall driven by a propagating low-pressure weather system from the Bay of Bengal which overlapped with the ongoing Monsoon precipitation system from the Indian ocean (Sudheer et al., 2019).
Most reservoirs in the region, which were primarily hydropower-driven, were already at or near maximum capacity prior to the peak precipitation event, leading to complete loss of flood moderation capabilities (Suresh et al, 2024). Another example of hydropower dam operations negatively affecting downstream flooding was seen in the 2011 Thailand Mega flood, that killed more than 800 people, due to a record high precipitation event (Gale & Saunders, 2013). The weakness of existing operations of major hydropower dams such as Bhumibol and Sirikit dams, due to rigid reservoir operations, was considered one of the main reasons (Loc et al., 2023; Poaponsakorn & Meethom, 2017). Similarly, the Volta River in Ghana, has also witnessed multiple flooding across the years due to unexpected releases from the Bagre hydropower dam in Burkina Faso (Abass et al., 2022). Most of the time, such floods were attributed to hydropower reservoir operations. In this case, lack of transboundary cooperation and timely sharing of reservoir operations data only exacerbated the downstream flood management challenges in Ghana. A similar case in point is in the upper Indus basin between India (upstream) and Pakistan (downstream) where the downstream Mangla Dam of Pakistan on the Jhelum River is often forced to spill large amounts of water due to unexpected transboundary release from India.
As seen from these recent historical events, there appears to be an increasing trend, albeit unverified, where hydropower dams appear ‘flood-inducing’ in many places. At the same time, global sustainability strategies aimed at decarbonising the energy sector are driving international calls for an annual expansion in hydropower capacity at a rate of 2% (IHA, 2022). In a changing climate where precipitation patterns are becoming more variable and extreme and reservoirs are constantly losing storage due to sedimentation, it is therefore timely to re-examine hydropower dams of the developing world and ask if they are making some of the regions more flood prone.
Since more than one-third of the global population lives within 50km of major hydropower dams (Fan et al., 2022), understanding the dynamics between hydropower expansion and flood risks is timely not only for planning future hydropower projects but also for policy making to protect downstream communities from potential flood hazards and catastrophic loss of life.
Holistic approach to flood risk
Ultimately, the future of hydropower must involve a holistic approach that addresses its dual roles in energy production and flood control. By combining robust policy frameworks, technological innovations, and interdisciplinary research, the sustainable management of hydropower dams should be explored, ensuring they continue to benefit communities, while minimising flood risks in downstream regions and ecosystems.
If hydropower dams are causing more floods downstream than mitigating them in many developing regions of the world, then the price of development may become too much to pay for access to energy.
We call for a paradigm shift in hydropower planning and management, emphasising the integration of adaptive flood risk mitigation into energy production strategies while also adapting to anticipated changes in climate and land cover with a robust sedimentation management strategy during the dam’s service lifespan.
References
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Fan, P., Cho, M.S., Lin, Z., Ouyang, Z., Qi, J., Chen, J., Moran, E.F., 2022. Recently constructed hydropower dams were associated with reduced economic production, population, and greenness in nearby areas. Proceedings of the National Academy of Sciences, 119(8), p.e2108038119, https://doi.org/10.1073/pnas.2108038119
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