Dams + Climate Change = Bad News
By Samantha Stahl
Updated by Alec Kahn (March 2025)
The United States has over 10,000 dams, second only to China which has a staggering 24,000 [i]. With climate change causing water shortages and storm surges, this might seem like good news. Dams store water, provide renewable energy, and prevent floods. Unfortunately, however, they also worsen the impacts of climate change. They release greenhouse gases, destroy carbon sinks in wetlands and oceans, deprive ecosystems of nutrients, destroy habitats, increase sea levels, waste water, and displace poor communities.
Crumbling, badly maintained dams also create a flood risk––endangering lives and putting significant financial strain on local governments and industry.
Dams = Water Loss
Our systematic overuse of freshwater, in addition to the already worsening effects of climate change, creates a need for artificial reserves. According to the United States Geological Survey, Americans withdraw 322 billion gallons per day (BGD) from the nation’s water systems; 12 percent for public water supply, 37 percent for irrigation, and 41 percent for thermoelectric power [ii]. The average American uses more than 300 gallons of water per day––and that doesn’t include the water required to produce their food, electricity, or household goods [iii].
While dams might appear to conserve water through storage, the reality is more complicated.
Generally, reservoirs and artificial lakes have a larger surface area than the rivers and channels that feed them. Larger surface areas expose more water to the sun, which speeds up evaporation. And, due to the nutrient-rich water from trapped sediment, dams and reservoirs also promote aquatic plant growth. The plants’ transpiration contributes to the already heightened evaporation rate. Every year, about 340 cubic kilometers of water evaporates from the world’s reservoirs [iv]. This accounts for roughly 7 percent of all freshwater consumed by human activities [v].
For instance, a study conducted by the European Water Association on the evaporation rate from artificial and municipal lakes and reservoirs in Istanbul concluded that the amount of evaporation per year was equal to the city’s water needs for about 26 days [vi].
This evaporation also affects the microclimates of the surrounding areas, disrupting natural temperature fluctuations, ecosystems, and habitats. For example, increased evaporation in the region of a large dam changes the moisture concentration of the air, leading to increased heavy rainfall [vii]. This deprives the surrounding areas of their traditional rainfall patterns, placing stress on ecosystems and municipalities that depend on those patterns. It also leads to an increased rate of storm surges, which can create more frequent and intense flooding than the dam was designed to handle.
Meanwhile, dams disturb the flow and composition of the water within rivers and channels. Water released downstream from dams has unnaturally high energy and very little sediment, which causes “hungry water” to run forcefully downstream, eroding riverbeds without sufficient sediment to offset their losses [viii]. This deepens the riverbed compared to the surrounding water table, which causes the groundwater to rush into the channel and become surface water––a process known as incision [ix].
Incision is a natural process in the life of rivers and channels, but exacerbated incision, caused by rapid erosion, results in the draining of surrounding groundwater. This can have devastating consequences for communities that rely on groundwater for agriculture and drinking water, as well as for the global climate. One study estimated the depletion of groundwater reserves as accounting for 25% of global sea level rise [x].
According to the United Nations Environment Program, half of the world’s river basins have already been vastly depleted [xi]. This creates a vicious cycle, where growing demand requires more dams to keep up with fresh water usage. Surface and groundwater depletion then accelerates too quickly for natural replenishment to be possible.
Dams = Habitat Destruction
Any dramatic change in river composition stresses both up- and downstream habitats. Habitat loss is the leading cause of extinction.
Dams disrupt fish and bird migration. The change in the composition of the river interferes with the chemical signals guiding species through their biological processes. And the physical barrier of the dam blocks species from their traditional spawning and rearing locations. As a result of this, along with pollution and the effects of climate change, freshwater species have lost 84 percent of their populations since 1970 [xii].
For instance, since the completion of the Lower Granite Dam in 1975, the population of Sockeye Salmon in Snake River has severely declined. Between 1985 and 2007, only about 18 of the salmon returned to Idaho each year [xiii]. Despite progress during the Biden Administration, the movement to breach the Snake River dams and restore salmon habitats has yet to achieve a significant breakthrough [xiv].
Meanwhile, changes in the timing and flow of the rivers can create conditions that threaten the survival of the species that have evolved to live there. Any alteration in the structure and composition of the river can have disastrous effects on the surrounding species, in many cases leading to extinction.
Downstream ecosystems suffer from the lack of sedimentation in the water that flows over the dam. Normally, nutrient rich sediment regulates and provides nourishment to downstream habitats. But reduced sedimentation creates less fertile soil, stunting the growth of dependent species. The lack of vegetative growth can lead to erosion and to the destabilization of the surrounding areas [xv].
Downstream habitats are also severely impacted by changes in salinity and oxygen levels. Due to the high rate of evaporation and growth of aquatic vegetation within the reservoir itself, water that travels downstream from a dam usually has a higher salinity content and a lower oxygen concentration than normal [xvi][xvii]. This change in the chemical makeup of the water creates detrimental conditions for species that previously thrived in those areas.
Dams even have negative impacts on ecosystems and habitats upstream. Trapped nutrients can facilitate the growth of toxic algae blooms. Communities around the world from South Africa to California have had to impose drinking and swimming bans to protect people from water-borne illnesses, while some dams have killed off fisheries and entire aquatic ecosystems [xviii].
Even in less devastating circumstances, the new stagnant water environments created in the reservoir damage the conditions of the existing habitat. They also host non-native and invasive species that further undermine the integrity of the surrounding ecosystems.
Dams = Greenhouse Gases
As a source of hydroelectric energy, dams are often framed as a climate-friendly alternative to fossil fuels. But this does not account for their impact on global emissions.
Most reservoirs, especially those in tropical regions, emit significant amounts of greenhouse gases due to anaerobic bacteria that break down vegetation at the base of the reservoir, giving off carbon dioxide and methane. In 2020, dams were responsible for more than 5% of global methane emissions [xix].
Additionally, the changes to rivers’ timing, chemical and sediment composition, and flow lead to dramatic variations in floodplains and wetlands, which can cause the destruction of surrounding forests [xx]. Deforestation contributes significantly to climate change because the trees no longer store additional carbon dioxide, while their previously-absorbed carbon is released into the atmosphere. Meanwhile, the drying out of wetlands destroys another valuable carbon sink.
Dams are detrimental to carbon sinks in the ocean as well. Studies of the Amazon and Congo Rivers underscore how their nutrient- and sediment-rich water drives biological processes deep within the Atlantic Ocean, contributing to algal growth [xxi]. When those sediments and nutrients disappear, the conditions that support carbon dioxide-storing algae break down, destroying a crucial carbon sink along with it.
Blocking the sediments traveling downstream can also have devastating effects when river deltas are deprived of the silt they need to defend against damage from the ocean. Without the shoring up of river deltas and wetlands, inland ecosystems and human communities become even more vulnerable against the storm surges and sea level rises caused by climate change [xxii].
Dams = Earthquakes
Scientists have attributed over 100 earthquakes around the world to dams and reservoirs, a phenomenon known as Reservoir-Induced Seismicity [xxiii]. This happens when extra water seeps into the micro-cracks and fissures under the reservoir and surrounding areas and lubricates faults already under tectonic strain. The 7.9 Wenchuan Earthquake in China in 2008 killed 90,000 people and has been linked to the construction of the Zipingpu Dam [xxiv].
Dams = Trouble for people already affected by climate change
Dams have displaced around 80 million people worldwide [xxv]. From the people removed from dam building sites to the people who lose their homes to failing dams, most of the displaced communities come from impoverished areas already affected by climate change.
Dams that displace large populations often also result in human rights violations. Authoritarian governments in Burma, China, Colombia, Ethiopia, Guatemala, Sudan and other countries have responded to dam opposition with violence, intimidation, and threats. In one horrific dam-related incident, more than 400 Indigenous people died in the suppression of opposition to Guatemala's Chixoy Dam in 1982 [xxvi].
Meanwhile, old and failing dams generate further dangers and costs. According to the American Society of Civil Engineers, by 2030, seven out of 10 dams will be more than 50 years old [xxvii]. And already, over 2,000 state-regulated “high hazard” dams are in need of repair. These dams could result in a high loss of life if they fail. While dam construction technology has advanced and dams built today have improved, it would still cost an estimated $76 billion to secure the nation’s dams––not to mention the additional hundreds of billions of dollars needed for the rest of the world [xxviii].
Due to the high cost of maintenance and safety, many of the world’s dams get more dangerous as they age. The Mosul Dam in Iraq and the Kariba Dam in Zambia rank among the world’s most dangerous [xxix]. Should the Mosul Dam fail, it could result in the deaths of 500,000 people and deprive millions more of power and water. The 60-year-old Kariba Dam, meanwhile, jeopardizes the lives of 3.5 million people who live downstream of it. The dam’s collapse would leave 40 percent of South Africa without power and result in untold damages to surrounding wildlife, and could even lead to the destruction of another nearby dam, the Cahora Bassa [xxx].
The US also hosts several dams close to failure. In 2017, fear of the collapse of the Oroville Dam Spillway resulted in the evacuation of 200,000 people in northern California [xxxi]. While the dam remains intact, the eroding spillway, which is a critical piece of California’s flood control network, makes it difficult for the dam to manage heavy flows and rainfall. In 2024, during an extreme rainfall event in Minnesota, the century-old Rapidan Dam finally burst, causing massive damage to local infrastructure and raising fears about future dam failures from climate-related flooding [xxxii].
Growing recognition that old and eroding dams pose too high a risk have resulted in an increasing number of dam removals. The United States has taken down approximately 2,000 dams since 1912, with a majority of those dams removed in the last two decades, and 57 in 2021 [xxxiii]. Removing damaged and aging dams protects the surrounding population from disaster and allows the rivers to restore their natural and biological integrity.
Rights of Nature = Healthy Waterways + Sustainable Relationship
Fresh water is vital to the functioning of Earth’s hydrologic cycle, the maintenance of aquatic and surrounding ecosystems, and the support of human life. Preserving healthy and high functioning waterways contributes to controlling global temperatures and sustaining fresh water reserves, among countless other benefits.
Rivers are important in their own right, but also matter for their ability to maintain the health of surrounding river catchments, floodplains, and wetlands. If we continue to build dams that destroy our waterways’ ability to support vital ecosystems, we continue a historical paradigm that values short-term progress and developmental achievement over the sustainable health and integrity of Earth’s systems.
We will be on the path to a sustainable relationship with a healthier environment when we recognize that Earth has intrinsic rights to thrive, evolve and flourish. Earth law recognizes that Earth’s inherent rights are separate and distinct from property and ownership rights bestowed by humans. By actively promoting this new paradigm, we can forge a more balanced and reciprocal relationship between human activities and Earth’s natural systems.
Addressing the flaws in the traditional approach to development and acknowledging the rights and interests of waterways will enable us to better care for the planet and its resources. This will benefit humans too. By understanding sustainable water management and implementing those principles into our industry and governmental systems, we can better address the causes of waterway degradation. Through understanding what waterways need to function properly, we can create laws and regulations that can better outline the parameters of human activity.
Protecting waterway health must be one of the highest priorities when determining how water is used. If it is not, our waterways will continue to degrade and will be unable to provide the basic functions on which both nature and humankind depend.
To read about the Universal Declaration for Rights of Rivers, click here.
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