A new early warning satellite system has revealed that India along with Spain, Morocco and Iraq faces the risk of shrinking reservoirs that can lead to taps going dry.
It has highlighted poor rains in 2017 to show the shrinking of the Indira Sagar dam in Madhya Pradesh and the Sardar Sarovar reservoir in Gujarat that supplies drinking water to millions.
Shrinking reservoirs could spark the next "day zero" water crisis, according to the developers of a satellite early warning system for the world's 500,000 dams, the Gaurdian reported on Thursday.
Cape Town grabbed headlines on "day zero". It launched a countdown to the day when taps would be cut off to millions of residents as a result of a three-year drought. Drastic conservation measures have forestalled that moment in South Africa.
However, dozens of other countries face similar risks from rising demand, mismanagement and climate change, said the World Resources Institute (WRI).
The US-based environmental organisation is working with Deltares, the Dutch government and other partners to build a water and security early warning system that aims to anticipate social instability, economic damage and cross-border migration.
A prototype is due to be rolled out later in 2018, but a snapshot was unveiled on Wednesday that highlighted four of the worst-affected dams and the potential knock-on risks.
Tensions have been apparent in India over the water allocations for two reservoirs connected by the Narmada river. Poor rains last year left the upstream Indira Sagar dam a third below its seasonal average.
When some of this shortfall was passed on to the downstream Sardar Sarovar reservoir, it caused an uproar because the latter is a drinking supply for 30 million people. Last month, the Gujarat government halted irrigation and appealed to farmers not to sow crops.
Spain has suffered a severe drought that has contributed to a 60 per cent shrinking of the surface area of the Buendia dam over the last five years, the Guardian report said.
All the dams are in the mid-latitudes, the geographic bands on either side of the tropics where climate change is expected to make droughts more frequent and protracted. As more reservoirs are scanned, the WRI expects more cases to emerge.
"These four could be a harbinger of things to come," said Charles Iceland of the WRI. "There are lots of potential Cape Towns in the making. Things will only get worse globally, as water demands increase and the effects of climate change begin to be felt."
Gennadii Donchyts, senior researcher for Deltares, said the reservoir-monitoring service will steadily grow in size as information is added from Nasa and European Space Agency satellites that provide resolutions of between 10 and 30 metres on a daily basis.
The petabytes of data are analysed using Google Earth Engine and algorithms to compensate for periods where parts of the surface area are covered by cloud, the Guardian report said.
