With projections of supply and demand for freshwater veering off in opposite directions, global warming represents the worst possible intervention. Rising planetary temperatures will accelerate the pump of the water cycle through faster evaporation from land, rivers, lakes and oceans. A warmer and more volatile atmosphere will receive this added moisture, with uncertain consequences.

The implications for rainfall are of course the subject of intensive research. There is broad agreement that monsoon patterns will change in timing and intensity, that arid and semi-arid regions will become drier, and that extremes of drought and flooding will become more frequent. Rising sea levels will aggravate the problem of groundwater salinity.

Much uncertainty remains, not least in mapping climate predictions on national or regional areas that coincide with the political reach of water management policy. Even where predictions of rainfall trends are confident, there is insufficient understanding of the mechanics of run-off and groundwater recharge to fully grasp the implications. The same is true for the consequences of the melting of the world’s glaciers which together account for 40% of global irrigation. The net impact on crop yields and soil conservation is also uncertain.

Climate change and water scarcity therefore present policymakers with a perfect storm of known and “known unknown” threats. Planning of vital freshwater infrastructure has become fraught with risk, even for the most sophisticated municipal authorities.

Reports already suggest that the impact of global warming will add hundreds of millions of people to the global count of those affected by water scarcity, including the lack of safe drinking water. An obvious example is the Nile Delta, where salinization caused by rising sea level threatens the fertility of a densely populated region.

Whilst the effect of climate change on the El Nino and La Nina phenomena is likely to considerable, the detail remains very difficult to anticipate. The El Nino that concluded in 2016 has been assessed as one of the strongest on record. It is widely considered to have contributed to the concentration of drought-related humanitarian crises spilling over into 2017 – in Cambodia, Bolivia, India, Ethiopia, and Kenya, amongst others.

Nature offers little sympathy to hesitation and uncertainty in response to challenges of water scarcity. Stories of delivering water by train in the Indian state of Maharashtra and the 2011 emergency water relief for the Pacific island of Tuvalu deliver a preview of water scarcity in a warming world.

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more Water Scarcity briefings (updated April 2018)
Definitions
Water Cycle
Water Energy Food Nexus
Causes of Water Scarcity
Solutions to Water Scarcity
Sustainable Development Goal for Water
Access to Safe Water
Water Wars
Source material and useful links