The climate in dryland regions has fluctuated between wet and dry conditions for the last 500,000 years.

Many of the landforms found in drylands today were formed during previous wet conditions.

Periods of wet conditions in drylands are known as pluvials and can last thousands of years.

In the Sahara Desert, the most recent pluvial was between 6,000 and 10,000BP (before present). This pluvial was caused by the migration of the ITCZ (Inter-Tropical Convergence Zone) to the north, bringing wetter conditions and the spread of grassland and forest. During this time, rainfall was as high as 600mm per year, leading to the formation of river systems.