Global Freshwater Scarcity

4/14/2015 climate change , ecosystem services , food , overuse , regime shifts , water 0 Comments

Human pressure on the Earth’s Biosphere is so large that geologists have announced that we live in a new era, the Anthropocene, in which humanity is the largest driving force of global change. The mounting stresses on the biosphere to support 7,3 billion (to become 9 billion) people may cause collapses and major shifts in ecosystems, from local to global scales. The ability to generate social and economic well-being is now threatened. Freshwater is at the centre of this change.

Freshwater is the bloodstream of the terrestrial Biosphere. Greenwater (used by plants) and blue water (rivers and groundwater) are linked across all scales. It is a resource that supports human health, industry and energy generation. Many water systems have undergone ‘regime shifts’ whereby disturbances forces the water ecosystem to flip to an alternative stable state. For example, the Baltic Sea has gone from a low nutrient clear state to a high nutrient murky state due to eutrophication and overfishing. Potential future regime shift, with global implications, include the dieback of the Amazonian rainforest, Arctic ice loss and the Atlantic deep-water formation.

Food production is the world’s largest user of freshwater. In many countries such as Brazil and China diets are changing to include more meat and dairy product which increases food water requirements. Globally, as much as 40% of the grain produced is converted to animal feed. By 2050, currently available water for croplands will not be sufficient for producing enough food for humanity. Agricultural water management is key to lowering freshwater depletion rates and increasing farm productivity. Global consumptive use of blue water has been estimated at 2600 km3 per year. Several regions already suffer from the widespread impacts of the overuse of blue water. River basins with withdrawals exceeding more than 40-60% of available water resources experience severe water scarcity. The number of people living in areas which suffer from blue water scarcity is soaring. In 2005, about 35% of the global population where living in areas with chronic water shortage.

About half of the river water withdrawn for societal use has evaporated, literally consumed during use, and about 25% of the rivers on land are highly affected by overuse of blue water. River depletion is considerable in irrigated regions of the world and many economically important river basins are already surpassing their ecological limits. Blue water security is subject to a high level of vulnerability to change in both Asia and Africa. For example, the Indus and Ganges-Brahmaputra-Meghna basins upon which some 1.5 billion people depend are highly vulnerable to change. Zones of particular concern are north-western India, the north China plain, the Great Plains of the US and the Central Valley in California. At the national scale, 5 countries are withdrawing more groundwater than can be recharged in aquifers, these include: Saudi Arabia, Libya, Egypt, Pakistan and Iran. 

Until recently, humans have been able to assume that precipitation was relatively stable and predictable. However, new insights now show that this assumption no longer holds. Climate change is a major driving force of a changing water landscape and its projected that a 2 °C increase in average global temperatures will result in an increase of 40% of people living in absolute water scarcity. Floods and droughts will become more prominent and rainfall patterns could change. There are large uncertainties about future rain, monsoon and snow patterns that influence river flows. Glacial melt has been widely observed in the mountain water towers of the world, including the Himalayas, the Andes, the Alps and the Kilimanjaro.