Enough fresh water is lost from continents each year to meet the needs of 280 million people. Here’s how we can combat that.
Earth’s continents are drying out at an alarming rate. Now a new report paints the most detailed picture yet of where and why fresh water is disappearing – and outlines precisely how countries can solve the problem.
Continental drying is a long-term decline in the availability of fresh water over large continental areas. It is caused by the accelerated melting of snow and ice, thawing of permafrost, water evaporation and groundwater extraction. (The report’s definition excludes meltwater from Greenland and Antarctica, the authors noted.)
Continents have now overtaken ice sheets as the largest contributors to sea level rise, because regardless of its origin, lost fresh water eventually ends up in the ocean. The new report reveals that this contribution amounts to approximately 11.4 trillion cubic feet (324 billion cubic meters) of water each year, enough to meet the annual water needs of 280 million people.
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Considerable impacts
THE report was published on November 4 by the World Bank. Its results are based on 22 years of data from NASA’s GRACE mission, which measures small changes in Earth’s gravity resulting from the movement of water. The authors also compiled two decades of economic and land use data, which they integrated into a hydrological model and a crop growth model.
The average amount of fresh water lost each year from continents is equivalent to 3% of the world’s annual net “income” from precipitation, according to the report. This loss rises to 10% in arid and semi-arid regions, meaning continental drying is hitting dry areas like South Asia harder, Zhang said.
This is a growing problem. In a study published earlier this year, Zhang, Famiglietti and their colleagues showed that distinct dry zones rapidly coalesce into “mega-dry” regions.
“The impact is already being felt,” Zhang said. Regions where agriculture is the largest economic sector and employs the most people, such as sub-Saharan Africa and South Asia, are particularly vulnerable. “In sub-Saharan Africa, dry shocks reduce the number of jobs by 600,000 to 900,000 per year. If you look at who is affected, the hardest hit are the most vulnerable groups, such as landless farmers.”
Countries that do not have a large agricultural sector are also indirectly affected, as most of them import food and goods from dry regions.
The consequences on ecosystems are also dramatic. Continental drying increases the likelihood and severity of wildfires, and this is particularly true in biodiversity hotspots, according to the report. At least 17 of 36 globally recognized biodiversity hotspots – including Madagascar and parts of Southeast Asia and Brazil – are showing a declining trend in freshwater availability and are at increased risk of wildfires.
“The implications are so profound,” Famiglietti told Live Science.
The biggest culprit
Currently, the main cause of continental drying is the extraction of groundwater. Groundwater is poorly protected and undermanaged in most parts of the world, meaning the past few decades have been a “free for all” pumping, Famiglietti said. And the hotter and drier the world becomes because of climate changethe more groundwater is likely to be extracted, as soil moisture and glacial water sources begin to decline.
However, better regulations and incentives could reduce excessive groundwater pumping. According to the report, agriculture is responsible for 98% of the global water footprint, so “if agricultural water use efficiency is improved to a certain baseline level, the total amount of water that can be saved is enormous,” Zhang said.
Globally, if water use efficiency for 35 key crops, such as wheat and rice, improved to median levels, enough water would be saved to meet the annual needs of 118 million people, the researchers found. There are many ways to improve water use efficiency in agriculture; for example, countries could change where they grow certain crops to match freshwater availability in different regions, or adopt technologies such as artificial intelligence to optimize the timing and quantity of irrigation.
Countries can also set limits on groundwater extraction, encourage farmers through subsidies and increase the price of water for agriculture. Additionally, the report shows that countries with higher energy prices have slower drying rates because pumping groundwater costs more, improving water use efficiency.
Overall, water management nationwide is working well, according to the report. Countries with good water management plans have depleted their freshwater resources two to three times slower than countries with poor water management.
Virtual water trading
Globally, virtual water trading is one of the best solutions for water conservation if done right, Zhang said. Virtual water trade occurs when countries trade fresh water in the form of agricultural products and other water-intensive goods.
Global water consumption increased by 25% between 2000 and 2019. A third of this increase occurred in regions already drying out – including Central America, northern China, Eastern Europe and the southwestern United States – and much of the water was used to irrigate water-intensive crops with inefficient methods, according to the report.
There has also been a global shift toward more water-intensive crops, including wheat, rice, cotton, corn and sugarcane. Out of 101 drying countries, 37 have increased the cultivation of these crops.
Virtual water trading can save huge amounts of water by offshoring some of these crops to countries that don’t dry out. For example, between 1996 and 2005, Jordan saved 250 billion cubic feet (7 billion cubic meters) of water importing wheat from the United States and corn from Argentina, among other products.
Globally, between 2000 and 2019, virtual water trading saved 16.8 trillion cubic feet (475 billion cubic meters) of water each year, or about 9% of the water used to grow the world’s 35 most important crops.
“When water-poor countries import water-intensive products, they are actually importing water, which helps them preserve their own water supplies,” Zhang said.
However, virtual water trading is not always that simple. This could benefit one country suffering from water scarcity, but severely deplete another country’s resources. An example is the production of alfalfaa water-intensive legume used in livestock feed, in dry regions of the United States for export to Saudi Arabia, Famiglietti said. Saudi Arabia benefits from this exchange because the country does not use its water to grow alfalfa, but Arizona aquifers are dryhe said.
Reasons to be optimistic
The solutions identified in the report fall into three broad categories: managing water demand, increasing water supplies through recycling and desalination, and ensuring fair and efficient water allocation.
If we can make these changes, sustainable use of fresh water is “very possible,” Zhang said. “We have reason to be optimistic.”
Famiglietti agreed that small changes could go a long way.
“It’s complicated because the population is growing and we’re going to need to produce more food,” he said. “I don’t know if we’re going to get through this with technology, but when we start thinking about decadal timescales, about policy changes, about changes in financial innovations, about technological changes, I think there’s reason to be optimistic. And over those decades, we can continue to think about how to improve our lot.”
Some of the views expressed in this article are not included in the World Bank report. They should not be construed as having been endorsed by the World Bank or its representatives.
