By Tim Radford, Climate News NetworkThis piece first appeared at Climate News Network.

LONDON — Droughts by the end of this century somewhere in the world will be 20% more frequent. But the catch is that nobody right now can predict with any certainty which places will feel the effects soonest, or more frequently.

Thirty research teams from 12 countries report in the Proceedings of the National Academy of Sciences that unless greenhouse gas emissions are reduced on a global scale, an extra 40% more people are likely to experience real water scarcity.

While some will have too little water, others might have too much. Of the areas investigated, more than half could also expect increases in river flooding.

The areas most likely to experience drier climates and more prolonged droughts include the Mediterranean, the Middle East, the southern USA and southern China.

Southern India, western China and parts of east Africa could experience what one author, Simon Gosling of the University of Nottingham, UK, calls “substantial increases in available water.”

Neither such predictions of drought nor the admissions of uncertainty are in any way new. The significance of the latest research perhaps lies in its scale, its thoroughness and the fact that it confirms, once again, the unhappy picture of climate change in a world which resolutely goes on burning fossil fuels (this is always called “the business as usual” scenario”).

Uneven effects

The study incorporated five global climate models to simulate ways in which climate change might affect flood hazard, drought, water scarcity, agriculture, ecosystems and even the spread of malaria.

The interpretations of such simulations are always spoken of in terms of “signal to noise ratio” and of “global hotspots”; and of probabilities and trends rather than predictions. But the overall conclusion is that drought severity is on the increase and some places are going to feel the impact of climate change worse than others.

The research was led by Christel Prudhomme of the UK Centre for Ecology and Hydrology, who said: “Our study shows that different representations of terrestrial water cycle processes in global hydrological models are responsible for a much larger uncertainty in the response of hydrological drought to climate change than previously thought. We don’t know how much changed climate patterns will affect the frequency of low flows in rivers.”

A warmer world inevitably means more evaporation, and warmer air temperatures mean that the capacity of the atmosphere to carry water vapour will also increase.

But where the extra water will fall is still unresolved. “More water under climate change is not necessarily always a good thing”, says Simon Gosling.

“While it can indeed help alleviate water scarcity, assuming you have the infrastructure to store it and distribute it, there is also a risk that any reductions in water scarcity are tempered by an increase in flood hazard.”

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