Drought warning as the tropics expand

California’s governor, Arnold Schwarzenegger, warned on Thursday that his state “is headed toward one of the worst water crises in its history”.

Now new research suggests that the three-year drought in the Golden State may be a consequence of the expanding tropics, which are gradually growing as human emissions of greenhouse gases warm the planet.

…Reichler says that the expansion of the subtropics is more feared than the widening of the tropical zone itself. While the tropical belt is hot and humid, the subtropics suffer from severe drought. The Sahara and Sahel are both subtropical regions.

The climate models quoted by the Intergovernmental Panel on Climate Change predict that the Mediterranean region and the south-west of the US are heading towards devastating droughts. Reichler says this latest study suggests this is a result of the poleward march of the tropics.

Southern California is already subtropical in the summer. But with climate change, dry conditions could spread to areas like northern California, Washington and Utah, which now get far more rain and snow.

New Scientist