Ancient drought

"Humans have a long history of having to deal with climate change", said Christopher Bernhardt, now a researcher with the U.S. Geological Survey. He was talking about the collapse of ancient Egyptian civilisation 4200 years ago, in a time of an "abrupt and global mega-drought". Climate and drought lessons from ancient Egypt using fossil pollen to augment historical records — press release

The drought that consumed Ancient Egypt extended across the Northern Hemisphere from Europe to Asia, and lasted for centuries. Usually droughts lasting longer than 35 years are called mega-droughts. This drought lasted 300 years. The 4.2 ka BP event in the Levant — research article

The mega-drought brought unimaginable hardship. The Egyptian sage Ipuwer wrote "the desert claims the land, towns are ravaged, Upper Egypt became a wasteland". The fall of the Egyptian Old Kingdom — BBC The epitaph of Ankhtifi, a local Egyptian ruler, described desperate hunger and cannabilism. Ankhtifi — Wikipedia The disaster marked the end of Egypt's Old Kingdom, and the last of the pyramids. The fall of the Egyptian Old Kingdom — BBC

This was easily one of the most destructive mega-droughts in human history, but it was not the last.

Civilisation and drought

Up to present day, mega‑droughts have brought thirst and famine, and the end of civilisations.

Scientists have implicated mega-droughts in the downfall of the Assyrians in 7^th century B.C. Climate may have helped crumble one of the ancient world’s most powerful civilizations — research article, the Mayans around a thousand years ago, Severe droughts explain the mysterious fall of the Maya — BBC and the great Khmer civilisation based in Angkor Wat, Cambodia, in the 13^th and 14^th centuries. How water built and destroyed this powerful empire — National Geographic

Each mega-drought triggered a cascade of disasters. The Mayan civilisation ended in exodus, as people left in search of water. Severe droughts explain the mysterious fall of the Maya — BBC The Khmers, weakened by decades of mega-drought and floods, were invaded by their Thai neighbours. How water built and destroyed this powerful empire — National Geographic

In its final decades, the Assyrian civilisation was "littered with political instability, civil wars, and invasion by outside armies", all triggered by drought, according to Adam Schneider, co-author of a recent study of the Assyrian collapse. Climate may have helped crumble one of the ancient world’s most powerful civilizations — research article

Mega-droughts to come

Around the world, droughts are already increasing in number.

During the early years of the twentieth century, the number of droughts each year could mostly be counted on one hand. Droughts used to be a rare event. This changed in the 1960s. The number of droughts each year quickly moved into the double digits, and it has kept on climbing ever since.

Drought disasters becoming more frequent around the world. Author's own work. Based on data from EM-DAT: The Emergency Events Database - Université catholique de Louvain (UCL) - CRED, D. Guha-Sapir - www.emdat.be, Brussels, Belgium.

The hardest hit regions, according to the EU scientists, will be "most of Africa, Australia, southern Europe, southern and central United States, Central America, the Caribbean, north‐west China, and parts of Southern America." Global changes in drought conditions under different levels of warming — research article

As well as becoming more frequent, droughts are forecast to get much longer.

Currently an average drought lasts 7 months. At 3 °C (5.4 °F) warming an average drought would last for a year and a half.

Droughts similar to or even worse than the longest, most severe droughts in recent memory, such as Australia's Millenium Drought, Africa's Sahel Drought, or the US's Dustbowl Drought, could take place 2 or even 5 times per decade, depending on global warming.