Saudi Arabia now known for its vast deserts and arid climate, was once a land shaped by flowing rivers, large lakes and fertile grasslands, according to a growing body of scientific research. Multiple international studies suggest that the Arabian Peninsula experienced long periods of humid and green conditions in the past, supporting wildlife and repeated human settlement.
Today, nearly 95 per cent of Saudi Arabia is covered by desert, including the Arabian Desert and the Rub’ al Khali, or Empty Quarter. Despite this, recent scientific evidence shows that extreme dryness is not the region’s permanent natural state. Researchers say dramatic climate shifts over millions of years repeatedly transformed Arabia into a habitable landscape.
Much of this transformation occurred during the Pleistocene Epoch, which lasted from about 2.6 million to 11,700 years ago. During this period, global climate cycles caused major shifts in rainfall patterns. While ice sheets advanced and retreated in the Northern Hemisphere, monsoon systems expanded into Arabia, bringing sustained rainfall.
Studies combining satellite imagery, archaeology and geological analysis have identified thousands of ancient river channels and lake beds across the peninsula. From space, what appear today as dry and barren landscapes reveal the outlines of once-extensive water systems.
According to Michael Petraglia, professor of human evolution and prehistory at the University of Oxford, advanced satellite technology has allowed scientists to map more than 10,000 ancient lakes across Arabia, including in areas that are now completely dry. Fossil remains of elephants, hippos, crocodiles and molluscs found at several sites further confirm the presence of long-lasting wet environments capable of sustaining large animals.
One of the most striking discoveries comes from the Rub’ al Khali, the largest continuous sand desert in the world. New research led by King Abdullah University of Science and Technology, in collaboration with several international institutions, reveals that the region once contained a massive lake covering around 1,100 square kilometres and reaching depths of up to 42 metres. During wetter phases between about 11,000 and 5,500 years ago, this lake overflowed, carving a valley more than 150 kilometres long through the desert.
Scientists believe these wet periods were driven by the northward expansion of African and Indian monsoons. Although the duration of these green phases varied across the peninsula, they repeatedly created habitable corridors for humans and animals.
Archaeological evidence found along ancient rivers and lakes shows that early human populations hunted, gathered and lived in these environments for extended periods. Researchers say Arabia was not merely a harsh transit route for early humans leaving Africa, but a destination that supported long-term settlement.
Around 6,000 years ago, rainfall declined sharply, and the region gradually returned to arid conditions. This forced human populations to migrate once again, reshaping settlement patterns across the Middle East and beyond.
Additional evidence comes from cave formations known as stalagmites. Chemical analysis of these mineral deposits reveals long-term rainfall records, showing that central Saudi Arabia remained green for much of the last eight million years. These findings challenge the idea that deserts stretching from the Sahara to the Thar Desert were permanent barriers to human movement.
The scientific discoveries align with Saudi Arabia’s current efforts to combat desertification. Under the Saudi Green Initiative, the kingdom has pledged to plant 10 billion trees and restore nearly 75 million hectares of degraded land. By mid-2025, more than 151 million trees and shrubs had already been planted, with a target of exceeding 600 million trees by 2030.
Experts say the research into Arabia’s green past not only reshapes understanding of human history but also offers valuable lessons for modern land restoration. As climate change intensifies, scientists believe studying these ancient ecosystems could help guide sustainable solutions for arid regions worldwide.