How Deserts Form Next to Oceans

Exploring the atmospheric and geographic factors that create coastal desert ecosystems

Published on Feb. 22, 2026

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Many of the world's driest deserts, like the Atacama in Chile and the Namib in southern Africa, are located right next to vast oceans. This seeming paradox is the result of a complex interplay of vertical and horizontal air movement, as well as the influence of mountain ranges. Equatorial heat, trade winds, and rain shadows all contribute to the formation of these unique coastal desert environments.

Why it matters

Understanding the dynamics behind coastal desert formation is crucial as climate change intensifies, potentially leading to the expansion of existing deserts and the creation of new ones. This could have significant impacts on water resources, biodiversity, and human populations in these fragile ecosystems.

The details

According to hydrologist David Kreamer, the formation of coastal deserts hinges on three key factors: vertical air movement, horizontal air movement, and the interaction of air moisture with mountain ranges. Equatorial heat causes air to warm and rise, creating low-pressure systems that fuel lush forests. However, this rising air then spreads outward and descends in the subtropical regions, suppressing cloud formation and leading to desert development. Trade winds also play a crucial role, tending to drop moisture on the eastern sides of continents and leaving the western coasts exceptionally dry. Mountain ranges exacerbate this effect, forcing moist air to rise, cool, and release precipitation on the windward side, while the leeward side remains arid.

  • The Atacama Desert in Chile is generally considered the driest non-polar desert on Earth.
  • Many of the world's hot and dry deserts sit between 20 and 40 degrees north or south of the equator.

The players

David Kreamer

A hydrologist at the University of Nevada, Las Vegas who studies groundwater contamination, groundwater-dependent ecosystem sustainability, and water supply in Africa.

Seattle

A city that receives approximately 39.3 inches of rain annually.

Yakima

A city located on the eastern side of the Cascade Mountains that receives only 8 inches of rain annually.

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What’s next

Innovations in water harvesting technologies, such as fog collection systems inspired by Namib beetles, offer potential solutions for mitigating water scarcity in coastal desert regions.

The takeaway

The formation of coastal deserts is a complex interplay of atmospheric and geographic factors, and understanding these dynamics is crucial as climate change intensifies, potentially leading to the expansion of existing deserts and the creation of new ones, with significant impacts on water resources, biodiversity, and human populations.