As the urgency of climate change calls for a transition away from fossil fuels, hydropower could usher in a cleaner and more sustainable energy system as mandated by SDG 7. But these benefits should be weighed against the negative social, geopolitical, and environmental costs.
Understanding the social cost of dams
As one of the oldest forms of man-made infrastructure, dams have been integral to economic development throughout human history. They are built to control floods, irrigate crops, supply water, generate electricity, and ease navigation. Proponents of dams often praise them as a source of low-carbon electricity, but harnessing the power of the river comes with concentrated costs.
The construction of dams, especially large dams and those located in transboundary river basins, has wide-ranging socioeconomic, geopolitical, and environmental implications. Large dams, such as the Three Gorges Dam in China (see figure below for before vs. after satellite images around the dam location), displace millions of people globally and deprive entire communities of their cultural heritage1. The displaced rarely receive adequate compensation and often suffer from an enduring loss of land, job, and wealth long after the dams are built. By modifying and fragmenting rivers, dams also exacerbate water scarcity and worsen geopolitical tensions2,3. As these socioeconomic and geopolitical costs are often borne by marginalized and indigenous people near the dam catchment area, dams could exacerbate existing social and environmental injustice.
Beyond the socioeconomic and geopolitical implications, dams affect the ecological functioning of river systems by reducing the downstream transfer of nutrients and threatening the natural habitat of freshwater megafauna, especially migratory fish species4-6. Nevertheless, climate change mitigation requires a rapid and systematic transformation of the energy system toward renewable sources, and hydropower plays a pivotal role. As a result, understanding the costs and benefits of dam construction is crucial for energy and climate policy.
Figure 1: The Three Gorges Dam uprooted more than 1.5 million people
Gaps in existing data
Quantifying the net benefit of dams requires a comprehensive database with three key characteristics: 1) accurate geo-coordinates of dams, 2) information on completion year, and 3) global in coverage. Existing databases of dams either lack necessary spatial and temporal detail or are limited in scope. Some countries, such as India, have national dam registries, but they are poorly documented and difficult to access. For domestic policymakers, international organizations, advocacy groups, and nongovernmental organizations, the lack of an up-to-date global database with fine geospatial detail is a severe hindrance. Compared with more extensive knowledge about the flow, development, and spread of fossil fuel projects, the baseline data available on hydropower is lacking. This is especially unfortunate as the world is currently experiencing a global boom in dam construction7. Yet, against the backdrop of this boom is a notable gap in the knowledge on how to quantify dams' environmental, socioeconomic, and geopolitical impacts.
The Global Dam Tracker (GDAT)
To fill this gap, we compile a new global database of dams, the Global Dam Tracker (GDAT). The data collection process is quite labor-intensive and requires a range of skills. In particular, we collected extensive primary data from governments and NGOs, examined institutional backgrounds to validate records on the design features of dams, and geo-referenced the locations of dams and their corresponding catchments. More than 90% of dams in GDAT are geocoded (n = 31,780), and the coordinates are extensively verified using Google Earth and other geospatial software. Beyond location, GDAT contains detailed attribute information for each dam, such as completion year, purpose, height, length, and installed capacity. As such, GDAT is one of the most comprehensive geo-referenced global dam databases with catchment and attribute information to date, especially for the Global South.
Figure 2: GDAT dam locations and catchments
To allow for inter-temporal analysis of the impact of dam construction, we use an algorithm to derive the catchment areas corresponding to GDAT dams. Using various state-of-the-art satellite data products that span the past three decades, we calculate the changes in surface-water coverage induced by dam construction. Between 1984 and 2018, an area of more than 50,000 km2 has become seasonally or permanently covered with water due to the construction of dams. This area, larger than the size of the Netherlands, demonstrates that dams have substantially altered the location and persistence of surface water around the world.
Figure 3: Dams substantially increase global surface water coverage
The GDAT database could be used for a systematic and global analysis of the impact of dams on local communities. As the urgency of climate change calls for a transition away from fossil fuels, hydropower could usher in a cleaner and more sustainable energy system as mandated by SDG 7. But these benefits should be weighed against the negative social, geopolitical, and environmental costs.