Where Has All the Water Gone?
(Yasmin Siddiqi)
MANILA March 22 : We live on a parched planet. Farmers till arid
pastureland, and policymakers fret over empty reservoirs, dry rivers, and
thirsty cities. And that only scratches the surface – literally – of the
world’s water problem. Subterranean aquifers, which amount to the world’s
reserve water tank, are also running dry. If this continues, the consequences
could be dire, especially for water-stressed and fast-growing Asia.
Subterranean aquifers are repositories of water located deep
underground, in permeable rock, soil, or sand. And they contain about 100 times
the amount of water found on the earth’s surface, in streams, lakes, rivers,
and wetlands. If you’re in central Africa, South America, or some parts of
Europe, you’re probably standing just a few hundred feet above one.
Surface water resources, such as desalinated seawater or
recycled wastewater, will not close the global gap – predicted to reach 40% by
2030 – between water supply and demand. So subterranean aquifers are
increasingly being exploited for agriculture, power generation, and daily use
in fast-growing cities (urban Asia is growing at a rate of 120,000 people per
day).
Today, about 30% of the world’s liquid freshwater comes from
subterranean aquifers. And one-third of the 37 largest aquifers studied by the
University of California between 2003 and 2013 were severely depleted,
receiving little or no replenishment from rainfall. Some of the most stressed
aquifers are in the driest regions, including Asia, up to 88% of which is
water-stressed.
Asia contains around one-third of the world’s land irrigated by
groundwater, with India, China, and Pakistan being the biggest consumers. South
Asia alone accounts for half the groundwater used globally. But Asia’s aquifers
– many of which were formed millennia ago, when areas like northern China had a
more humid climate – are no longer being replenished regularly by rainfall.
Instead, boreholes are getting deeper and water tables are
falling. In Pakistan’s Punjab Province, over-pumping is lowering the water
table by up to a half-meter (20 inches) per year, threatening future food and
water security and making thirsty crops like sugarcane and rice tougher to
grow.
Asia’s surging population – which could jump by 25%, topping
five billion, by 2050 – will put even more stress on food, energy, and water
supplies. Globally, 60% more food will be needed by then, with agriculture
soaking up increasingly scarce freshwater. Climate change will exacerbate
conditions further.
But the problem extends beyond water depletion. Over-pumping of
groundwater is already leading to soil subsidence, causing some Asian cities to
sink. By 2030, as much as 80% of North Jakarta could be below sea level. Parts
of Beijing are sinking by several centimeters per year, according to some
estimates.
Moreover, depleted aquifers near coastlines are prone to
contamination from saltwater, rendering land barren. Some aquifers are
contaminated by arsenic, which can occur naturally deep underground. Nature
Geoscience estimates that more than 60% of groundwater in the Indo-Gangetic
aquifer is contaminated by arsenic or salt. In Bangladesh, water tainted by
arsenic is blamed for more than 40,000 deaths each year.
The first step toward remedying this situation is to establish
precisely how much groundwater is left and how it is being used – not easy, but
not impossible either. NASA’s Gravity Recovery and Climate Experiment satellite
provides information on changes in the earth’s gravity due to fluctuating water
volumes. And by applying remote sensing technology to river basins, we can
determine how much surface water is available and who is consuming what.
Another important step is to improve the pricing of groundwater.
China has run a pilot program in which farmers had to pay extra if they pumped
more than their allocation. Similar approaches have worked well in Australia
and Mexico. But such measures can be politically difficult to implement. The
key to success will be to help countries not only to design the right policies,
but also to create the legal frameworks needed to establish and enforce them.
Even more politically difficult would be the elimination of
electricity and gas subsidies, which encourage farmers to pump groundwater all
day. If such subsidies can’t be withdrawn, there are innovative alternatives
that could curb over-pumping.
For example, in Gujarat, India, the government has reduced
groundwater pumping by offering power for just eight hours per day. Farmers
have the power they need, but can’t pump all day long. Another approach could
be to buy back surplus power from farmers to feed into the grid. That would not
just reduce over-pumping, but also help to supplement rural incomes.
Efforts to replenish aquifers could also be pursued. A pilot
program in India’s Uttar Pradesh state collects excess floodwater in storage
ponds, from which water seeps into the water table.The final step would be to
improve management of surface water, thereby reducing the temptation to turn to
groundwater in the first place. Around 80% of wastewater is returned untreated
to rivers, often contaminating them. Taking stronger action to stop this would
be far simpler – including logistically and politically – than conserving
groundwater.
Subterranean aquifers should be the reservoir of last resort. If
we don’t protect them today, future generations will pay a steep – or even an
existential – price.Yasmin Siddiqi is Principal Water Resources Specialist at
the Asian Development Bank.
