The Sahara is often seen as an inhospitable environment, but it once gave birth to the ancient Garamante Empire, which thrived by tapping hidden underground water. However, unsustainable use leads to the depletion and eventual decline of these resources, underscoring the critical importance of sustainable groundwater management.
With little rainfall and soaring temperatures, the Sahara is often considered one of the most extreme and inhospitable environments on Earth. In the distant past, the Sahara was once lush and green, but an ancient society living in a climate very similar to today's found a way to harvest water from the seemingly dry Sahara - and thrive until the water dried up.
Latest discoveries about the Garamante Empire
The latest research report recently presented at the "GSAConnects2023" conference of the Geological Society of America describes how a series of accidental environmental factors enabled the ancient Saharan civilization - the Garamante Empire - to exploit underground groundwater, allowing the society to sustain for nearly a thousand years until the water source was exhausted.
"Societies rise and fall based on the rise and fall of physical systems, so there is a special function for humans to grow there," said Frank Schwartz, a professor in the College of Geosciences at Ohio State University and lead author of the study.
Between 11,000 and 5,000 years ago, monsoon rains transformed the Sahara Desert into a relatively lush environment, providing surface water resources and a habitable environment for civilization to flourish. When the monsoon rains stopped 5,000 years ago, the Sahara turned back into a desert and, with one unusual exception, all civilizations retreated from the area.
From 400 BC to 400 BC, the Garamantes lived in the desert of southwestern Libya, where extreme drought conditions were much the same as today, and they were the first urbanized society to establish in a desert without a continuously flowing river. The surface water lakes and rivers of the "Green Sahara" era were long gone by the time the Garamantes arrived, but luckily there was a large sandstone aquifer storing water underground - probably one of the largest in the world, according to Schwartz.
Cross-sectional view showing how the Foggara or Kanat works. A tunnel is built into the hillside sloping upwards with vertical shafts until groundwater reaches it. Groundwater then flows down the tunnel. Image credit: Courtesy of Frank Schwartz.
The camel trade route from Persia through the Sahara brought to the Garamantes the technology of collecting groundwater using fog screens or karats. This method involves digging a slightly sloping tunnel into a hillside, just below the water table. Groundwater will flow down the tunnel into the irrigation system. The Garamantes dug a total of 750 kilometers of underground tunnels and shafts to collect groundwater, with the greatest construction activity between 100 and 100 BC.
Understanding the hydrogeology of the Garamantes
Schwartz combined previous archaeological research with hydrological analysis to understand how the local topography, geology, and unique runoff and recharge conditions created ideal hydrogeological conditions for the Garamantes to mine groundwater.
"Their karez shouldn't actually work because the karats in Persia are replenished every year with snowmelt water, whereas here the replenishment is zero," Schwartz said.
The Garamante people had good environmental luck. The climate in the early days was relatively humid, the terrain was suitable, and the groundwater environment was unique, which allowed groundwater to be mined through fog gate technology. However, their luck ran out when the water table dropped below the atomized Gala Tunnel.
Map locations and satellite aerial imagery show the areas and landscapes where ancient societies and the Garamante people lived. Source: NASA/Luca Pietranera
According to Schwartz, two trends are particularly concerning. First, extreme environments are increasingly common in countries such as Iran. Second, the unsustainable use of groundwater is becoming increasingly common.
"Looking at modern examples like the San Joaquin Valley, people are using groundwater faster than it can be replenished," Schwartz said. "California had a very wet winter this year, but it came after 20 years of drought. If the trend of dry years continues, California will eventually have the same problem as the Garamantes. Replenishing depleted groundwater supplies can be costly and ultimately impractical."
With no new water to replenish the aquifers and no surface water available, water shortages contributed to the decline of the Garamante Empire. The Garamante story serves as a warning about the power of groundwater as a resource and the dangers of overusing it.