Earth’s continents are drying up at an alarming rate. Now, a new report has painted the most detailed picture yet of where and why fresh water is disappearing — and outlined precisely how countries can address the problem.
Continental drying is a long-term decline in fresh water availability across large land masses. It is caused by accelerated snow and ice melt, permafrost thaw, water evaporation and groundwater extraction. (The report’s definition excludes meltwater from Greenland and Antarctica, the authors noted.)
Continents have now surpassed ice sheets as the biggest contributor to global sea level rise, because regardless of its origin, the lost fresh water eventually ends up in the ocean. The new report found this contribution is roughly 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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Far-reaching impacts
The report was published Nov. 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 shifting water. The authors also compiled two decades’ worth of economic and land use data, which they fed into a hydrological model and a crop-growth model.
The average amount of fresh water lost from continents each year is equivalent to 3% of the world’s annual net “income” from precipitation, the report found. This loss jumps to 10% in arid and semi-arid regions, meaning that continental drying hits dry areas such as South Asia the hardest, Zhang said.
This is a growing problem. In a study published earlier this year, Zhang, Famiglietti and their colleagues showed that separate dry areas are rapidly merging into “mega-drying” regions.
“The impact is already being felt,” Zhang said. Regions where agriculture is the biggest economic sector and employs the most people, such as sub-Saharan Africa and South Asia, are especially vulnerable. “In sub-Saharan Africa, dry shocks reduce the number of jobs by 600,000 to 900,000 a year. If you look at who are the people being affected, those most hard hit are the most vulnerable groups, like landless farmers.”
Countries that don’t have a large agricultural sector are also indirectly affected, because most of them import food and goods from drying regions.
The consequences for ecosystems are dramatic, too. Continental drying increases the likelihood and severity of wildfires, and this is especially true in biodiversity hotspots, the report found. At least 17 of the 36 globally recognized biodiversity hotspots — including Madagascar and parts of Southeast Asia and Brazil — show a trend of declining freshwater availability and have a heightened risk of wildfires.
“The implications are so profound,” Famiglietti told Live Science.
The biggest culprit
Currently, the biggest cause of continental drying is groundwater extraction. Groundwater is poorly protected and undermanaged in most parts of the world, meaning the past decades have been a pumping “free-for-all,” Famiglietti said. And the warmer and drier the world gets due to climate change, the more groundwater will likely be extracted, because soil moisture and glacial water sources will start to dwindle.
However, better regulations and incentives could reduce groundwater overpumping. According to the report, agriculture is responsible for 98% of the global water footprint, so “if agriculture water use efficiency is improved to a certain benchmark, the total amount of the water that can be saved is huge,” 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 like artificial intelligence to optimize the timing and amount of irrigation.
Countries can also set groundwater extraction limits, incentivize farmers through subsidies and raise the price of water for agriculture. Additionally, the report showed that countries with higher energy prices had slower drying rates because it costs more to pump groundwater, which boosts water use efficiency.
Overall, water management at the national scale works well, according to the report. Countries with good water management plans depleted their freshwater resources two to three times more slowly than countries with poor water management.
Virtual water trade
On the global scale, virtual water trade is one of the best solutions to conserve water if it is done right, Zhang said. Virtual water trade occurs when countries exchange fresh water in the form of agricultural products and other water-intensive goods.
Global water use increased by 25% between 2000 and 2019. One-third of that increase occurred in regions that were already drying out — including Central America, northern China, Eastern Europe and the U.S. Southwest — and a big share 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, maize and sugar-cane. Out of 101 drying countries, 37 have increased cultivation of these crops.
Virtual water trade can save huge amounts of water by relocating some of these crops to countries that aren’t drying out. For example, between 1996 and 2005, Jordan saved 250 billion cubic feet (7 billion cubic meters) of water by importing wheat from the U.S. and maize from Argentina, among other products.
Globally, from 2000 to 2019 virtual water trade 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-scarce countries import water-intensive products, they are actually importing water, and that helps them to preserve their own water supply,” Zhang said.
However, virtual water trade isn’t always so straightforward. It might benefit one water-scarce country but severely deplete the resources of another country. One example is the production of alfalfa, a water-intensive legume used in livestock feed, in dry regions of the U.S. for export to Saudi Arabia, Famiglietti said. Saudi Arabia benefits from this exchange because the country isn’t using its water to grow alfalfa, but aquifers in Arizona are being sucked dry, he said.
Reasons for optimism
The solutions identified in the report fall into three broad categories: manage water demand, expand water supply through recycling and desalination, and ensure fair and effective water allocation.
If we can make those changes, sustainable fresh water use is “definitely possible,” Zhang said. “We do 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 grow more food,” he said. “I don’t know that we’re going to ‘tech’ our way out of it, but when we start thinking on decadal time scales, changes in policy, changes in financial innovations, changes in technology — I think there is some reason for optimism. And in those decades we can keep thinking 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 interpreted as having been endorsed by the World Bank or by its representatives.
