How Deserts Form Next to Oceans: Unpacking the Meteorological and Geographical Factors

United States - Ekhbary News Agency

The Enigma of Coastal Deserts: Where Aridity Meets Abundance

Deserts are universally recognized for their extreme dryness, often conjuring images of vast, parched landscapes far removed from any significant water sources. Yet, paradoxically, some of the planet's most arid regions are found bordering expansive oceans. Iconic examples like the Atacama Desert in Chile and the Namib Desert in southern Africa dramatically illustrate this phenomenon, stretching along coastlines. The fundamental question then arises: how do these intensely dry environments materialize in close proximity to abundant oceanic water?

Scientific consensus points to three primary factors that facilitate the formation of coastal deserts. According to Dr. David Kreamer, a hydrologist at the University of Nevada, Las Vegas, these elements involve the vertical and horizontal movement of air, and the interplay between mountain ranges and atmospheric moisture.

Atmospheric Dynamics: Pressure Systems and Global Wind Patterns

Globally, a significant number of deserts are situated in bands approximately 20 to 40 degrees north and south of the equator. This geographical distribution is linked to the Earth's atmospheric circulation patterns. At the equator, intense solar radiation warms the air, causing it to rise. As this warm, moist air ascends, it creates a low-pressure system. The moisture within this rising air cools, condenses into clouds, and precipitates, leading to the lush rainforests, such as the Amazon, found in equatorial regions.

This equatorial air then spreads poleward at high altitudes before descending between 20 and 40 degrees latitude. In these subtropical belts, the descending air is dry and suppresses cloud formation, creating high-pressure zones that are inhospitable to rain. This atmospheric mechanism is a key reason for the existence of vast deserts like the Sahara and the Kalahari in these latitudes.

Complementing this vertical atmospheric motion is the horizontal transport of air. The prevailing trade winds near the equator blow from east to west. As these winds travel across continents, they tend to release their moisture on the eastern, windward sides. Consequently, the western, leeward sides of continents often become significantly drier. Physical geographer Abi Stone from the University of Manchester explains that in the case of the Namib Desert, any rainfall typically occurs in the mountains to the east, rather than within the desert itself.

The Influence of Cold Ocean Currents and Topography

Cold ocean currents exert a profound influence on coastal climates. When air masses move across these frigid currents, they cool down and absorb some moisture. However, this cooling stabilizes the air significantly, inhibiting convection – the vertical mixing necessary for cloud development. Stone likens these stable air masses to balloons that cannot expand upwards effectively. This trapped, cool, moist air remains close to the surface. While it may not produce rain, it can lead to persistent fog along the coast, a characteristic feature of many western coastal deserts.

Mountain ranges also play a crucial role in exacerbating aridity. When moist air is forced to ascend over a mountain barrier, it cools, and its moisture condenses, resulting in precipitation on the windward slopes. As the air descends on the leeward side, it is significantly drier, creating a "rain shadow" effect. The contrast between Seattle, west of the Cascade Mountains, which receives abundant rainfall, and Yakima, east of the Cascades, which is arid, serves as a clear illustration of this phenomenon.

In the Atacama Desert's context, prevailing winds originating from the Atlantic deposit moisture over the eastern part of South America, including the Amazon basin. Upon reaching the Andes Mountains, the air loses substantial moisture. By the time it descends onto the Pacific coast of Chile, it is exceptionally dry, contributing to the Atacama's status as one of the driest places on Earth.

Unique Adaptations in Extreme Environments

Coastal deserts possess distinct characteristics compared to their inland counterparts. They generally experience more moderate temperatures and greater climatic stability. Furthermore, these environments harbor unique flora and fauna that have evolved remarkable adaptations for survival. For instance, certain beetles in the Namib Desert have developed the ability to harvest atmospheric moisture by positioning themselves to collect fog droplets on their bodies.

The principles governing desert formation extend even to the polar regions, such as Antarctica and the northern Arctic. Despite being covered in ice, these areas are classified as deserts due to extremely low precipitation levels. The frigid air temperatures mean the atmosphere can hold very little moisture. Additionally, strong katabatic winds and surrounding ocean currents around Antarctica effectively block weather systems from penetrating the continent, maintaining its arid conditions.

Understanding these interconnected meteorological and geographical factors is essential for comprehending how seemingly contradictory landscapes—arid deserts flourishing beside vast oceans—come into existence and sustain unique ecosystems.

Ekhbary News Agency