Middle East climate predictions 'less certain'

Climate change induced water shortages in the Middle East are not as certain as previously thought, according to a study, emphasising the need for more regionally specific models.

Previous studies have indicated that climate change will cause major water shortages in the Middle East (see UN: climate danger for Middle East, North Africa).

Jason Evans, a research fellow at the Climate Change Research Centre at the University of New South Wales in Sydney, Australia, looked at climate predictions for the region based on both global and Middle East specific models.

The study based on global models, published in Climate Change last month (29 July), predicted a loss of about 170,000 square kilometres of viable rain-fed agricultural land, a longer dry season and changes in the timing of maximum rainfall.

However, a second study using a regional model indicated an annual rainfall increase of over 50 per cent around the Euphrates-Tigris watershed, which feeds the two largest rivers in the Middle East. The study will be published in an upcoming issue of the Journal of Hydrometeorology.

"There are regional scale phenomena not captured by the global climate models that can substantially change the projected climate change for particular regions," Evans told SciDev.Net. "So while the global models provide good estimates of the change at large scales, they can be quite wrong in particular locations."

"To capture these particular phenomena the resolutions need to increase by about ten times," Evans says.

The regional model picked up the effect of mountain ranges on low-level winds. These winds can transport large amounts of water vapour over hundreds of kilometres. When the winds meet the mountain ranges, they do not simply move over them but instead turn and travel parallel to them, often with increased speed, bringing rain to the headwaters of the Euphrates and Tigris river systems. 

Evans warns that further research is needed, since the study is based on only one regional model, which must be repeated to confirm the effect.

But the differences between these studies highlight the need to consider both modelling scales for future climate planning, he says.

"Under the global model scenario you would have to plan for dealing with droughts, while under the regional model scenario you need to plan for more heavy rainfall events, potential flooding, and landslides," says Evans.

Nasredin Hag Elamin, a policy officer at the UN Food and Agriculture Organization Regional Office in Cairo, Egypt, stressed the need for more regional data for policy planning.

"Water availability predictions resulting from accurate, scientific and confirmed studies using regional or even national models that give a close up picture on specific countries are more convenient for use in policy planning by agriculture policymakers than global models that give a general worldwide view."