When you think of a desert, you might picture endless sand and no water in sight. But some of the driest deserts, like the Atacama in Chile and the Namib in southern Africa, sit right next to oceans. How can that be? Let’s break it down simply.
Three main factors create these coastal deserts: how air moves up and down, how it moves horizontally, and the impact of mountains on moisture. David Kreamer, a hydrologist from the University of Nevada, shared that warm air rises, creating low pressure. This process forms clouds and rain in tropical areas near the equator, making them lush, like the Amazon rainforest.
As the warm air rises, it spreads out and cools down, sinking back down between 20 and 40 degrees north and south of the equator. This sinking air stabilizes weather, preventing cloud formation and leading to many deserts in regions like the Sahara and Kalahari.
Air movement also plays a big role. Near the equator, trade winds blow east to west. These winds drop moisture mainly on the eastern sides of continents, leaving their western coasts dry. For example, in the Namib, rain mainly falls in the mountains to the east, not directly in the desert.
Another key factor is cold ocean currents. When air moves over cold currents, it cools and stabilizes. Abi Stone, a physical geographer from the University of Manchester, explains that this cooler air carries moisture but doesn’t rise much. As a result, it can create foggy conditions along the coast instead of rain.
Mountains influence dryness, too. When moist air hits a mountain, it cools on the way up, dropping rain on one side. By the time it descends on the other side, much of the moisture is gone, creating a rain shadow. For instance, Seattle gets around 39.3 inches of rain per year, while Yakima, just east of the Cascade Mountains, sees only about 8 inches.
The Atacama Desert is a prime example of rain shadow effects. Here, winds drop rain over the Amazon and further lose moisture as they rise to cross the Andes. This leaves the Atacama extremely dry despite being next to the Pacific Ocean.
Coastal deserts are unique. They often have more stable temperatures and support plants and animals that have special adaptations to capture moisture. For instance, certain beetles in the Namib desert drink water from fog by turning their bodies towards it, showing how life adapts to harsh conditions.
Interestingly, polar deserts, like parts of Antarctica and the Arctic, share some similarities with warm coastal deserts. Cold temperatures prevent air from holding moisture, and strong winds can block weather systems from entering these regions. These dynamics help explain why these areas are just as arid as their hot desert counterparts.
In conclusion, coastal deserts illustrate the fascinating interplay of climate, geography, and life. Understanding these factors enriches our appreciation of the diversity of Earth’s ecosystems.
