UNO and WWF warn of river destruction
In the release of its World Water Development Report this week, the United Nations warns that most of the world's 500 largest rivers could be severely damaged or even destroyed in the near future due to drying out or intense pollution [1].
The construction of dams on the world's twenty longest rivers is already preventing the water from being transported unhindered into the sea. This not only affects the ecological carrying capacity of the watercourses, but also local fisheries in many places. Some streams, such as the Yellow River in China or the Colorado River in North America, usually no longer reach their delta at all because of the high water consumption in their upper reaches. Today, only two billion cubic meters of water flow into the mouth of the Nile instead of the previous 32 billion, and the Indus in South Asia has already lost ninety percent of its former volume.
Even in Europe, low water levels occur more frequently - like on the Rhine in 2003 - which, according to estimates by the United Nations, is likely to become more severe in the future due to global warming and increasing summer drought. In addition to the construction of dams, around 45,000 of which are currently blocking watercourses worldwide, researchers and hydraulic engineers are paying particular attention to climate change. Especially reservoirs in already dry regions such as northern China, the Middle East or the southwest of the USA lose ten percent of their capacity every year through evaporation: a value that will continue to increase with rising global temperatures.
According to a study, the nature conservation organization WWF also reports that only a third of 177 rivers with a length of more than a thousand kilometers are completely free of barrages and flow unhindered from the source to the mouth [2]. Most of them are in Asia and North and South America. In Europe, only the Petschura in Russia meets these criteria. Due to the current dam construction dynamics in Asia, the WWF fears that by 2020 most of these previously unobstructed rivers will have been blocked. Larger projects are currently also affecting the Mekong and the Yangtze River.
