Environment | A paradigm shift


Sarath Suresh and Faisal Hossain from the University of Washington in the US give their opinion on the complex relationship which exists between hydropower development and downstream flood risk


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


Below: Figure 1. [Top]. World map – Regions with high precipitation and steep topography shown in yellow where hydropower dams need to provide flood control. [Bottom]. Location of major dams (GranD database, Lehner et al., 2011) with designated main use of hydropower generation (marked in red) and flood control (marked in blue). Note that in regions classified as mountainous with high precipitation (highlighted in yellow), hydropower dams dominate


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


38 | August 2025 | www.waterpowermagazine.com


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45