Yes, a desert can be next to an ocean, a phenomenon that challenges the typical expectation of coastal areas being moist and lush. These distinct regions are known as “coastal deserts.” Their existence demonstrates that proximity to a large body of water does not automatically guarantee high rainfall. These narrow strips of arid land are a result of complex atmospheric and oceanic interactions that actively inhibit precipitation, creating a paradox where the driest places on Earth are located directly beside a major moisture source.
Understanding Coastal Deserts
A coastal desert is defined as a desert whose border lies directly adjacent to an ocean or sea. These are one of the four main types of desert biomes globally and are typically found on the western edges of continents, often situated in the subtropical latitudes, between 20 and 30 degrees north and south of the equator.
The classification of these areas as deserts is based on extremely low annual precipitation, not just high temperatures. Deserts generally receive less than 250 millimeters (10 inches) of rainfall annually. This low precipitation is the defining metric, making them true deserts despite the moderating effect of the ocean on temperature extremes.
The Role of Cold Ocean Currents
The primary mechanism responsible for creating coastal deserts is the presence of cold ocean currents flowing parallel to the coastline. These currents, such as the Humboldt Current off South America or the Benguela Current off Africa, bring cold water from polar regions toward the equator, significantly cooling the air immediately above the ocean surface.
When this cool, moist air moves over the water and encounters the warmer land, a temperature inversion layer forms close to the surface. A blanket of cold, dense air is trapped beneath warmer air from inland, which stabilizes the atmosphere. This stable stratification prevents the air from rising high enough to cool, condense, and form rain-producing clouds.
The cold water also reduces the rate of evaporation, meaning the air mass over the ocean starts with less moisture. Any moisture present does not condense when the air moves over the slightly warmer land because its capacity to hold moisture increases with the warming. This atmospheric stabilization actively suppresses convection and rainfall, leading to hyper-arid conditions on the adjacent coast.
Unique Climatic Features
Coastal deserts exhibit a climatic paradox characterized by high relative humidity despite minimal rainfall. The cold ocean currents often cool the air to its dew point, resulting in the frequent formation of dense sea fog, known as advection fog. This fog often blankets the coastal strip, sometimes for hundreds of days a year, providing a significant source of moisture.
Life forms in these environments have developed specialized adaptations to utilize this non-pluvial moisture, with some organisms relying entirely on fog for survival. Specialized plants have leaf structures highly efficient at condensing water droplets directly from the fog. For instance, certain beetles in the Namib Desert “fog bask” by tilting their bodies to collect condensed water. The fog also helps moderate coastal temperatures, leading to a smaller diurnal temperature range compared to inland deserts.
Prominent Global Examples
Two prominent examples of this phenomenon are the Atacama Desert and the Namib Desert, both located on the western coasts of their respective continents. The Atacama Desert, stretching along the Pacific coast of Chile and Peru, is considered one of the driest places on Earth. Its extreme aridity is directly linked to the influence of the cold Humboldt (or Peru) Current.
The Namib Desert in Southern Africa runs along the Atlantic Ocean coast for over 2,000 kilometers. The Namib’s lack of precipitation is primarily caused by the cold Benguela Current, which stabilizes the air over the coast and inhibits rainfall. These examples illustrate how cold ocean currents create vast, arid landscapes immediately next to the sea.