1.5 billion people will depend on water from the mountains
Worldwide, water consumption has almost quadrupled in the last hundred years, and many regions can only meet their needs thanks to inflows from the mountains. In 30 years, a quarter of the lowland population will be dependent on water from the mountain regions. Only sustainable development can ensure this function of the mountains as the water towers of the earth.
Water is one of the key resources of the future: Many lowland regions around the world are dependent on inflows from mountain areas, not least because of the sharp increase in irrigation for agriculture. A study led by the University of Zurich quantifies this dependence for the first time by contrasting water supply and consumption in lowlands with inflows from mountains. Based on a high-resolution global model, the study provides detailed information around the globe on dependence on mountain water resources. The analyses were conducted over a large area using a regular grid and then compared for each river basin with an area of over 10,000 km2 . This allows very differentiated insights into the respective regional differences and peculiarities.
Dependence increases despite falling per capita consumption
"Until now, the focus has been mainly on river basins that originate in the high mountains of Asia," says Daniel Viviroli of the Institute of Geography at the University of Zurich. "But in many other regions, intensively farmed areas are also very dependent on water from mountainous areas. This is the case, for example, in the Middle East and North Africa, as well as in parts of North America, South America and Australia," adds the first author.
This dependence has increased massively since the 1960s - despite more efficient water use and declining per capita consumption. Whereas at that time only 7 percent of the lowland population was substantially dependent on contributions from the mountains, by the middle of this century this figure will have risen to 24 percent. This corresponds to about 1.5 billion people in the lowland areas. The focus is particularly on the catchment areas of the Ganges-Brahmaputra-Meghna, Yangtze and Indus rivers in Asia, the Nile and Niger in Africa, the Euphrates and Tigris in the Middle East and the Colorado in North America. For their calculations, the researchers assumed a medium scenario in terms of population growth and technological, economic and social development.
Functioning ecosystems and climate protection
"For the mountains to continue to serve as the Earth's water towers, sustainable development is needed. It should be a key interest of lowlanders to safeguard this function of the mountains," says Viviroli. For example, agricultural overuse should be prevented and functioning ecosystems ensured. In addition, climate protection plays a decisive role: due to rising temperatures, the melt water peaks from snow-covered mountains already occur several weeks earlier in some cases, making them less usable for summer agriculture. Adjustments to water management will therefore be necessary, and possibly also new infrastructure such as dams and canals.
"However, technical solutions go hand in hand with major ecological damage, and some rivers, such as the Indus, also have little potential for expansion," says Viviroli. For the future, it will be crucial that lowland and mountain regions work closely together, despite political, cultural, social and economic differences.
Literature
Daniel Viviroli, Matti Kummu, Michel Meybeck, Marko Kallio, Yoshihide Wada:Increasing dependence of lowland populations on mountain water resources. Nature Sustainability 2020. doi: 10.1038/s41893-020-0559-9
