A study, published in Earth’s Future, examined how climate change could shape water stress across international borders.
‘Water stress’ is a measurement of the ratio between water use and availability.
It’s predicted that the number of people exposed to water stress could double by 2050, depending on global attempts to keep global warming below 2C.
The number of people exposed to water stress could double by 2050 if efforts are not made to keep global warming below 2C above pre-industrial levels, and future population growth is high, a study finds.
This means an additional 380 million people could face water stress by mid-century when compared to the number in 2010.
Increases will be concentrated in the Middle East, North Africa, and south and central Asia – regions that already face significant challenges as a result of water stress, the lead author tells Carbon Brief.
Around two-thirds of the global population – four billion people – face water scarcity for at least one month a year in today’s world.
Water availability is affected by physical processes – such as the amount of rainfall, rate of evaporation, and the geology of the land surface and human management, through dams, groundwater extraction, and reservoirs.
For many countries, water availability is also shaped by the actions of other nations that lie further upstream. These shared water resources are described as “transboundary” and include, for example, major rivers that traverse multiple countries.
The focus here is on water stress. It is calculated as a water use-to-availability ratio because it captures well a simple intuition about how water use and availability relate. When water is abundant, water use generally has less impact than when water is in short supply.
Global emissions and population growth are low, the number of people facing water stress is instead expected to increase by 50%.
The maps below give a global view of water stress (left) – and relative change to water stress (right) – in 2050 under the low emissions and population scenario (top) and the high emissions and population scenario (bottom).
The left-hand map displays the expected water stress ratio for different regions in 2050, with 0-0.1 indicating no stress (yellow), 0.1-0.2 indicating approaching stress (dark orange), 0.2-0.4 indicating moderate stress (orange), 0.4-0.7 indicating high stress (red), and a ratio of more than 0.7 indicating chronic stress (dark red).
The right-hand map shows relative changes in stress from 2010 to 2050, with light to dark blue indicating lower stress and light to dark orange, indicating higher stress.
“There are not many new areas facing high water stress, but the stressed river basins will see even higher stress levels in the future. The largest increases were found to be North Africa, the Middle East, and south and central Asia.”
Climate change can alter local precipitation patterns, but also evaporation. All the water that comes to the Earth’s surface either goes away as a discharge – to rivers and streams and eventually the ocean – or it can evaporate. Climate change can have an essential role because evaporation is partly driven by solar radiation and temperature.
For instance, climate change can affect how much water flows from a water source to countries downstream. For example, a decline in snowfall on a mountain range can reduce the availability of water from snowmelt in the lowlands in spring and summer. However, human actions, such as large-scale water extraction from rivers and dam building, can also affect how much water passes from one country to the next.
The maps below show percentage changes in local water consumption (top) and availability (bottom) in 2050 when compared to 2010 under the high emissions and population growth scenario. On the maps, blue indicates a percentage decline, while red indicates a percentage increase.
The maps show how, in the future, consumption of water is likely to increase – particularly in sub-Saharan Africa and South America – while water availability is likely to fall. The large increases in consumption are driven by population growth, according to the study.
For these countries, a key target should be to “pressure global actors to decrease emissions.
It’s possible that as water becomes more scarce, it will no longer be viable to grow crops in many of these regions. When crops disappear, this could have [a knock-on effect] on water scarcity.
Source From : World Economic Forum