THE DRY FACTS

Drought has wreaked havoc throughout history, destroying crops and causing famine and conflict. And it could be getting worse. By Olive Heffernan.

DEFINING DROUGHT

Characterized by unusual and persistent dry weather, drought is caused by shifts in global weather patterns such as El Niño, but also increasingly by human-induced climate change. Identifying drought is difficult, however, so there is considerable uncertainty about whether it is getting any worse.

A LONG HISTORY

Serious droughts have occurred in Australia and Africa, among other regions, in recent decades, but more severe 'megadroughts' have occurred on virtually every continent throughout history.

4,200 YEARS AGO

GLOBAL MEGADROUGHT

Where: North America but spread to Europe, Africa and Asia. Lasted for several centuries.

Cause: Cooling of the North Atlantic, which reduced rainfall by as much as 30%.