5 droughts that changed human history

Reports of severe droughts are rarely out of the headlines as our world warms up. North Korea has said it's suffering the worst drought in 37 years, while the last five months have been the driest in the history of the Panama Canal, according to authorities.

A recent study says human activity could have exacerbated a century of such droughts.

NASA's Goddard Institute for Space Studies (GISS) compared historical precipitation and tree ring data between 1900 and 2005, finding that a "human fingerprint" - through human-manufactured greenhouse gasses - has had a significant impact on global drought risk.

The report argues this human impact is set to grow, potentially leading to "severe" consequences for humanity - including more frequent and severe droughts, food and water shortages, destructive wildfires and conflicts between people competing for resources.

It’s a sobering scenario that, if realized, would lengthen an already extensive list of droughts that have affected the trajectory of human history for thousands of years. Here are five of those droughts and how they are thought to have changed the world.

1. The drought that prompted the spread of humanity

DNA research suggests a series of megadroughts between 135,000 and 75,000 years ago may have been responsible for the first migrations of early humans out of Africa.

Scientists say that variable climate conditions made the land in parts of Africa frequently inhospitable for human habitation. Droughts may have limited access to fundamental resources, forcing inhabitants to migrate outside the continent to find sustenance.

2. The drought that changed ancient Egypt

Archaeologists investigating the royal tombs of Egypt's Old Kingdom found evidence of a drought that hit the Middle East and parts of Europe 4,500 years ago.

Some experts say it was that drought, rather than civil strife, that caused the fall of the pharaohs, who ruled Ancient Egypt for 3,000 years before the region became a province of the Roman Empire in 30BC.

3. The drought that destroyed the Mayans

The Mayan empire in Mesoamerica was hit by drought at the most vulnerable moment in its history.

Rapid population growth coincided with a halving of annual rainfall 1,200 years ago, causing crops to fail and a war with neighbouring nations over dwindling water resources to ultimately precipitate the demise of the Mayan civilization.

4. The drought that spread deadly diseases

The Dust Bowl in the Great Plains of the US Midwest and Canada in the mid-1930s drove two million people off the land and led to an outbreak of diseases.

At the time it was not realized that the dust transmitted measles, influenza and a fungal lung disease called Valley Fever. For people already weakened by malnutrition, these diseases often proved fatal.

5. China's 'Most Disastrous' Drought

While China has weathered numerous severe droughts throughout its history, perhaps none was as consequential as the 1928-1930 drought, which some experts have called "the most disastrous event in the 20th century in China." The drought led to a widespread famine, claiming the lives of anywhere between three million and 10 million people.

More recently, in mid-2017, Chinese authorities said a large northern region had experienced the worst drought on record, citing climate change as the culprit for extreme weather patterns throughout parts of the country.