Deserts can exhibit various landscapes—ranging from vast sand dunes to rugged canyons, arid steppe, and polar ice sheets. Nonetheless, the common characteristic among them is the absence of rainfall. Simply put, any region receiving less than 10 inches (25 centimeters) of precipitation annually is categorized as a desert, as indicated by Lynn Fenstermaker(opens in new tab), an ecologist at the Desert Research Institute in Reno, Nevada.
The dryness in deserts is a consequence of the limited rainfall. However, the query remains: what causes certain regions on Earth to receive significantly less precipitation than others, leading to the arid nature of deserts?
Majorly, global air circulation patterns play a pivotal role, Fenstermaker affirmed. Solar energy directly strikes the Earth at its equator, warming the air and causing it to lose moisture through evaporation. Subsequently, the warm, arid air ascends and moves towards the poles. Descending at approximately 30 degrees latitude, this warm, dry air contributes to the establishment of a Hadley cell circulation pattern, propelling the trade winds that facilitated early maritime explorations. This mechanism largely explains why numerous world-renowned deserts, including e.g., Sahara and the Gobi in the Northern Hemisphere, as well as the Kalahari in the Southern Hemisphere, are situated around these latitudes.
Nonetheless, the narrative is nuanced. Wind patterns interact with the topography, influencing the distribution of deserts. For instance, when air masses from the ocean collide with a mountain range, they discharge their moisture as precipitation on the windward slopes as they ascend. Conversely, as the air descends on the leeward side of the mountains, it remains devoid of moisture, resulting in aridity. In California, for instance, the Mojave Desert lies in the rain shadow of the Sierra Nevada, Fenstermaker emphasized.
Interior regions can sometimes be drier due to their considerable distance from extensive water bodies, causing the incoming air to be devoid of moisture by the time it reaches those areas, noted Andreas Prein(opens in new tab), an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colorado. This scenario is evident in the Gobi Desert in Central Asia, which is encased by the Himalayas.
Contrary to expectations, coastal regions aren’t always humidity-laden. Collisions between cold ocean currents and inland-moving air can produce fog. Upon reaching land, this fog retains its moisture in the atmosphere instead of precipitating, often creating coastal deserts such as the Atacama in Chile, renowned as one of the driest locations on Earth.
Deserts do not exclusively equate to sizzling climates; sections of the Arctic and Antarctic are recognized as deserts. According to Prein, frigid air has a diminished capacity for holding moisture compared to its warmer counterpart. Thus, the icy temperatures in these polar regions result in minimal precipitation, despite substantial water being stored as ice within the ground.
Pertaining to alterations in global climate patterns, the landscapes of deserts are subject to transformation. For instance, millennia ago, the Sahara region was adorned with lush grasslands and tropical forests(opens in new tab). Presently, climatic variations are reshaping desert boundaries worldwide.
“Due to climate change, there is a projected expansion of the Hadley cell towards higher latitudes,” as stated by Prein, augmenting the desertification-prone areas. Elevated temperatures can expedite this geographical shift by escalating water evaporation and further desiccating the air. Beyond mere rainfall, the equilibrium between precipitation and evaporation is pivotal in defining a desert, Prein emphasized.
“On a global scale, the anticipation is that escalating temperatures will culminate in heightened evaporation and the enlargement of existing arid regions,” noted Fenstermaker.
Human-induced alterations on the terrain also play a role. Deforestation to facilitate agriculture eradicates indigenous vegetation, with some studies hinting that deforestation in tropical regions diminishes precipitation levels(opens in new tab). If a large portion of water evaporates instead of being retained in the soil through plant uptake, it initiates a cycle that results in progressive aridity of the landscape. Marginal semi-arid zones neighboring existing deserts are particularly exposed to this vulnerability.
“The proliferation of deserts is generally a multifold outcome,” commented Prein. “It’s an amalgamation of various factors such as human intervention, climate change, and the innate climatic fluctuations that ultimately push ecosystems beyond the brink.”
Image Source: Vova Shevchuk / Shutterstock
