With projections of supply and demand for freshwater veering off in opposite directions, global warming represents the worst possible intervention.
About two-thirds of the world’s freshwater is frozen in glaciers, snow and ice, self-evidently vulnerable. 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 natural cycle for frozen freshwater in mountainous regions involves accumulation during winter and release of meltwater during summer. This seasonal availability of irrigation is vital to farming communities across vast areas, most notably those downstream of the Himalayas, embracing several South Asian countries.
Temperature increases across the Himalayan “water towers” currently exceed the average of global warming. Retreating glaciers and reduced snow cover threaten to disrupt crop yields for hundreds of millions of small farmers.
The implications of global warming for rainfall are of equal concern. 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. Whilst the effect of climate change on the El Nino and La Nina phenomena is likely to be considerable, the detail remains very difficult to anticipate.
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 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 significantly increase the global count of those affected by water scarcity, including the lack of safe drinking water. An example is the Nile Delta, where salinization caused by rising sea level threatens the fertility of a densely populated region.
Nature offers little sympathy to hesitation and uncertainty in response to challenges of water scarcity. Recent droughts in Cape Town and Chennai prompted the concept of “Day Zero”, the inauspicious moment when household taps would fail, a disconcerting preview of water scarcity in a warming world.