ome are as highly polluting as fossil fuel plants (the amount depends on their age, carbon inputs, and reservoir profile). Especially in the tropics, dam reservoirs are a globally significant source of methane, one of the most potent greenhouse gases. Even outside of the tropics, some dams can be significant sources of methane, as researchers have found for the draw-down zone at Three Gorges Dam4. Currently measuring reservoir emissions is not required for new projects, even though strong guidelines have been developed by UNESCO and the International Hydropower Association, of which China is a member.
Healthy rivers are critical for supporting life on Earth. Large dams however make it harder for people and ecosystems downstream to adapt to climate change, by reducing water quality and quantity, drying up forests and wetlands, flooding productive land, and destroying fisheries. Free-flowing rivers also play a crucial role in helping trap carbon. Scientists predict that damming the Amazon, the Mekong, the Congo5 and other high flow rivers in warm-ocean areas, could reduce the planet’s ability to mitigate climate change.
China’s dam-building hotspots collide with climate change
“China is home to half of the world’s dams …
…despite the poor record of dam construction and resettlement in China, the ambitious plans for developing huge dam cascades on some of China’s most pristine and diverse river basins in the southwest present serious safety and security challenges”
Katy Yan, International Rivers
China is home to half of the world’s dams. These projects have forced more than 23 million people from their homes and land, and many are still suffering the impacts of displacement. Dams have also taken a huge toll on China’s biodiversity, causing fisheries to suffer and driving endemic species such as the Baiji (Yangtze River dolphin) to extinction.
Despite the poor record of dam construction and resettlement in China, the ambitious plans for developing huge dam cascades on some of China’s most pristine and diverse river basins in the southwest present serious safety and security challenges. Many of the proposed dams are located in seismic and biodiversity hotspots, including the Three Parallel Rivers World Heritage Site, one of the most spectacular and biologically rich areas of the world. This region is also one of China’s most seismically active as well as ecologically fragile.
According to a government climate change assessment6 published last year, the concentration of rain during summer and autumn will increase, overwhelming rivers in the south, while long dry winters will increase and be especially crippling for those living in parched northwestern provinces. This collision of climate change impacts and China’s dam-building boom will likely result in the following:
- Higher risk of dam failures. China’s dams are not prepared for an increase in extreme weather events such as floods and heavy rains. The Nu Valley, for instance, experiences deadly mudslides during the wet season every year. A proposed dam cascade on the Nu River could exacerbate the impacts of greater precipitation in this region by increasing the risk of mudslides as a result of the removal of vegetation along the steep banks during construction. Planners need to consider the risk of dam breaches from both increased flows and seismic activity.
- Dam mismanagement exacerbates drought conditions. China’s plans to build more dams for power generation may increase tensions between upstream and downstream users during the dry season, and between the often conflicting objectives of energy, irrigation, flood control and ecosystem services. For instance, in 2011, central China was hit by its worst drought in five decades, which sharply reduced the power generation of the Three Gorges Dam and spurred widespread criticism of its role in potentially exacerbating drought conditions downstream. Modeling how climate change will affect water availability and river flows is difficult, but thus far, dam developers are simply ignoring such impacts on hydrology when designing n