Sudden, Severe Droughts Not Uncommon

Drought on the scale of North America's 1930s dust bowl struck 30 times in regions around the globe during the 20th century.

The severe droughts all began abruptly and lasted a decade or more. Most entailed a decline in precipitation of at least 10 percent compared with the area's average for the century.

Among the more well-known of these events, the American dust bowl lasted 14 years with precipitation at 10 percent below average. Africa's Sahel drought beginning around 1970 was even more extreme, where rainfall dropped 12 percent below normal for 17 years.

A harsh, lengthy dry spell afflicted eastern Africa in the 1920s and 1930s when they had 15 years with rainfall down by 15 percent. Eastern Australia around the same time experienced a 13 percent decline in precipitation. That was followed by a drought of similar severity in western Australia.

Drastic droughts have also plagued western Europe, northeast China, eastern Canada, India, Ukraine, northern Russia and Algeria, among other places. Since 1980, southern Africa and central Europe were hit by extended dry periods involving more than a 10 percent decline in rainfall.

Most droughts affected regions that are already quite arid, normally receiving 350 to 700 millimetres of precipitation a year. They always started with the climate suddenly turning dry within a few years. The droughts typically set in at a location from which they either strengthened and expanded or shifted to nearby regions.