The incidence of moderate drought will double to affect half the world by the end of the century unless greenhouse gas emissions are curbed, according to a study backed by the British government.
Computer modelling of the effect of global warming on water levels conducted by the Met Office, Britain’s official weather forecaster, also suggests that severe droughts could rise sharply, in the absence of action to limit emissions from the consumption of fossil fuels.
Worsening water shortages threaten to create growing problems of starvation and international conflict.
The Met Office predictions, to be published shortly in a US journal, are based on a projection of reasonably strong global economic growth, with no mitigation of greenhouse gas emissions. In that scenario, global temperatures rise by 1.3 to 4.5 degrees Celsius by the end of the century.
That would mean moderate drought – defined as water levels experienced during the driest fifth of months in a region in the past 50 years – occurring about 50 per cent of the time, the model indicates.
It also suggests a rise in extreme drought from 1 per cent at present to 30 per cent by the end of the century: although the Met Office scientists warned that they had less confidence in this prediction, as it was based on only a relatively small number of observations.
The incidence of moderate drought has already risen from about 15 per cent in the 30 or so years after 1950 to about 25 per cent today.
Because the definition of “drought” varies from place to place, its effects will differ.
Vicky Pope, head of the climate programme at the Met Office’s Hadley Centre, said: “In the UK a drought could mean a hosepipe ban and other restrictions in water use. In Africa, it could mean people not having enough water to live.”
The rise in drought predicted by the model is not uniform worldwide but is not confined to any specific continent or region, she said. Sub-Saharan Africa is one of the areas seen as suffering from more frequent droughts.
Andrew Simms of the New Economics Foundation, who discussed the Met Office findings at a fringe meeting at the Conservative party conference in Bournemouth on Tuesday, said: “Millions in Africa are already living under the shadow of drought.
Even small changes in rainfall can have severe negative effects. This research . . . reveals a fundamental disconnect between the scale of the problem and the current political response.”