- Brahma Chellaney writes that excessive damming and drastic overuse of water resources are causing the world’s major waterways to run dry.
Brahma Chellaney, South China Morning Post
Urgent action is needed to save the world’s rivers, including improving agricultural practices, which account for the bulk of freshwater withdrawals
Thanks to excessive damming and drastic overuse of water resources, an increasing number of major rivers across the world are drying up before reaching the sea. Nowhere is this more evident than in China, where the old saying, “Follow the river and it will eventually lead you to a sea,” is no longer wholly true.
While a number of smaller rivers in China have simply disappeared, the Yellow River – the cradle of the Chinese civilisation – now tends to run dry before reaching the sea. This has prompted Chinese scientists to embark on a controversial rainmaking project to help increase the Yellow’s flow. By sucking moisture from the air, however, the project could potentially affect monsoon rains elsewhere.
For large sections of the world’s population, major river systems serve as lifelines. The rivers not only supply the most essential of all natural resources – water – but also sustain biodiversity, which in turn supports human beings.
Yet an increasing number of rivers, not just in China, are drying up before reaching the sea. A major new United Nations study published early this month offers grim conclusions: human actions are irremediably altering rivers and other ecosystems and driving increasing numbers of plant and animal species to extinction. “Nature across the globe has now been significantly altered,” according to the study’s summary of findings.
Water sustains life and livelihoods and enables economic development. If the world is to avert a thirsty future and contain the risks of greater intrastate and interstate water conflict, it must protect freshwater ecosystems, which harbour the greatest concentration of species.
Yet, according to another study published in Nature this month humans have modified the flows of most long rivers, other than those found in the remote regions of the Amazon and Congo basins and the Arctic. Consequently, only a little more than one-third of the world’s 246 long rivers are still free-flowing, meaning they remain free from dams, levees and other man-made water-diversion structures that leave them increasingly fragmented.
Such fragmentation is affecting river hydrology, flow of nutrient-rich sediment from the mountains where rivers originate, riparian vegetation, migration of fish and quality of water.
Take the Colorado River, one of the world’s most diverted and dammed rivers. Broken up by more than 100 dams and thousands of kilometres of diversion canals, the Colorado has not reached the sea since 1998.
The river, which originates in the Rocky Mountains and is the lifeblood for the southwestern United States, used to empty into the Sea of Cortez in Mexico. But now, owing to the upstream diversion of 9.3 billion cubic metres (328.4 billion cubic feet) of water annually, the Colorado’s flow into its delta has been reduced to a trickle.
Other major rivers that run dry before reaching the sea include the Amu Darya and the Syr Darya, the two lifelines of Central Asia; the Euphrates and the Tigris in the Middle East; and the Rio Grande, which marks the border between Texas and Mexico before heading to the Gulf of Mexico. The overused Murray in Australia and Indus in Pakistan are at risk of meeting the same fate.
More fundamentally, altered flow characteristics of rivers are among the most serious problems for sustainable development, because they seriously affect the ecosystem services on which both humans and wildlife depend. Free-flowing rivers, while supporting a wealth of biodiversity, allow billions of fish – the main source of protein for the poor – to trek through their waters and breed copiously.
Free-flowing rivers also deliver nutrient-rich silt crucial to agriculture, fisheries and marine life. Such high-quality sediment helps to naturally re-fertilise overworked soils in the plains, sustain freshwater species and, after rivers empty into seas or oceans, underpin the aquatic food chain supporting marine life.
China’s hyperactive dam building illustrates the high costs of river fragmentation. No country in history has built more dams than China. In fact, China today boasts more large dams than the rest of the world combined.
China’s chain of dams and reservoirs on each of its long rivers impedes the downstream flow of sediment, thereby denying essential nutrients to agricultural land and aquatic species. A case in point is China’s Three Gorges Dam – the world’s largest – which has a problematic build-up of sediment in its own massive reservoir because it has disrupted silt flows in the Yangtze River.
Likewise, China’s cascade of eight giant dams on the Mekong, just before the river enters Southeast Asia, is affecting the quality and quantity of flows in the delta, in Vietnam. Undeterred, China is building or planning another 20 dams on the Mekong.
How the drying up of rivers affects seas and oceans is apparent from the Aral Sea, which has shrunk 74 per cent in area and 90 per cent in volume, with its salinity growing nine-fold. This change is the result of the Aral Sea’s principal water sources, the Amu Darya and Syr Darya, being so overexploited for irrigation that they are drying up before reaching what was once the world’s fourth-largest inland lake.
Compounding the challenges is the increasing pollution of rivers. Aquatic ecosystems have lost half of their biodiversity since the mid-1970s alone.
Urgent action is needed to save the world’s rivers. This includes action on several fronts, including improving practices in agriculture, which accounts for the bulk of the world’s freshwater withdrawals.
Without embracing integrated water resource management and other sustainable practices, the world risks a parched future.
Brahma Chellaney is the author of nine books, including Water, Peace, and War.