The Earth's continents are drying out at an alarming rate. Now a new report has painted the most detailed picture yet of where and why fresh water is disappearing, and outlines precisely how countries can tackle the problem.
Continental drying is a long-term decline in the availability of fresh water over large areas. This is caused by accelerated melting of snow and ice, thawing permafrost, water evaporation and groundwater withdrawal. (The report's definition excludes meltwater from Greenland and Antarctica, the authors note.)
Continents have now surpassed ice sheets to become the largest source of global sea level rise because, regardless of origin, lost fresh water eventually ends up in the ocean. The new report says 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.
Far-reaching consequences
report was published on November 4 by the World Bank. Its results are based on 22 years of data from NASAThe GRACE mission, which measures small changes in Earth's gravity resulting from the movement of water. The authors also collected two decades of economic and land use data, which they used in a hydrological and crop growth model.
The report says the average amount of freshwater lost each year from the continents is equivalent to 3% of the world's annual net rainfall “income”. This loss increases to 10% in arid and semi-arid regions, Zhang said, meaning continental drying is hitting dry areas such as South Asia the hardest.
This is a growing problem. In a study published earlier this year, Zhang, Famiglietti and their colleagues showed that individual dry areas are rapidly merging into “mega-drying” regions.
“The impact is already being felt,” Zhang said. Particularly vulnerable are regions where agriculture is the largest economic sector and employs the most people, such as sub-Saharan Africa and South Asia. “In sub-Saharan Africa, drought shocks reduce jobs by 600,000 to 900,000 per year. If you look at the people who are affected, the most vulnerable groups, such as landless farmers, will suffer the most.”
Countries that do not have a large agricultural sector also suffer indirectly, since most of them import food and goods from dry regions.
The consequences for ecosystems are also dramatic. The report says drying continents are increasing the likelihood and severity of wildfires, and this is especially true in biodiversity hotspots. At least 17 of the 36 globally recognized biodiversity hotspots, including Madagascar and parts of Southeast Asia and Brazil, are trending toward decreased freshwater availability and an increased risk of wildfires.
“The implications are profound,” Famiglietti told Live Science.
The biggest culprit
Currently, the main reason for the drying of the continents is the extraction of groundwater. Groundwater is poorly protected and poorly managed in most parts of the world, meaning pumping has been a “free for all” in recent decades, Famiglietti said. And the warmer and drier the world becomes due to climate changethe more groundwater is likely to be extracted as soil moisture and glacial water sources begin to deplete.
However, better regulations and incentives could reduce groundwater pumping. According to the report, agriculture accounts for 98% of the global water footprint, so “if water use efficiency in agriculture is improved to a certain level, the total amount of water that can be saved is enormous,” Zhang said.
The researchers found that globally, if water use efficiency for 35 key crops such as wheat and rice were raised to average levels, enough water would be saved to meet the annual needs of 118 million people. There are many ways to improve water efficiency in agriculture; for example, countries could change where certain crops are grown to ensure freshwater availability in different regions, or introduce technologies such as artificial intelligence optimize the timing and volume of watering.
Countries can also set limits on groundwater extraction, incentivize farmers through subsidies, and increase prices for agricultural water. Additionally, the report shows that in countries with higher energy prices, drying rates are slower because it costs more to pump groundwater, making water use more efficient.
Overall, national water management is performing well, according to the report. Countries with good water management plans depleted their freshwater resources two to three times slower than countries with poor water management.
Virtual water trading
According to Zhang, on a global scale, virtual water trading is one of the best solutions to save water if done correctly. Virtual water trade occurs when countries exchange fresh water in the form of agricultural products and other water-intensive goods.
Between 2000 and 2019, global water consumption increased by 25%. A third of this increase occurred in regions that were already experiencing drying, including Central America, North America and North America. ChinaAccording to the report, most of the water was used to irrigate water-intensive crops using inefficient methods.
There has also been a global shift towards more water-intensive crops, including wheat, rice, cotton, corn and sugarcane. Of the 101 dryland countries, 37 have increased their production of these crops.
Virtual water trading could save huge amounts of water by moving some of these crops to countries that are not experiencing drying. For example, between 1996 and 2005 Jordan 250 billion cubic feet (7 billion cubic meters) of water saved importing, among other things, wheat from the US and corn from Argentina.
Globally, from 2000 to 2019, virtual water trading saved 16.8 trillion cubic feet (475 billion cubic meters) of water annually, or about 9% of the water used to grow the world's 35 most important crops.
“When water-stressed countries import water-intensive products, they are actually importing water, and this helps them conserve their own water supplies,” Zhang said.
However, virtual water trading is not always so simple. This may benefit one water-stressed country but severely deplete another country's resources. One example is production alfalfaa water-intensive legume crop used as livestock feed in arid regions of the United States for export to Saudi Arabia, Famiglietti said. Saudi Arabia benefits from this exchange because the country does not use water to grow alfalfa, but Arizona's aquifers are being sucked dryhe said.
Reasons for optimism
The solutions identified in the report fall into three broad categories: managing water demand, expanding water supplies through recycling and desalination, and ensuring equitable and efficient distribution of water.
If we can make these changes, sustainable use of freshwater is “definitely possible,” Zhang said. “We have reason to be optimistic.”
Famiglietti agreed that small changes can make a big difference.
“It’s difficult because the population is growing and we will need to grow more food,” he said. “I don't know if we're going to get out of this with technology, but when we start thinking about the ten-year time scale, the changes in policy, the changes in financial innovation, the changes in technology – I think there's some cause for optimism. And in these decades, we can continue to think about how to improve our lives.”
Some views expressed in this article are not included in the World Bank report. They should not be interpreted as endorsed by the World Bank or its representatives.
