Deserts

Deserts are regions of the Earth that receive very little rainfall, usually less than 250 mm per year. They cover about one-fifth of the land surface and can be hot or cold, depending on their location and climate. Deserts are characterized by extreme temperatures, low humidity, sparse vegetation, and high evaporation rates.

Deserts are not lifeless wastelands, however. They are home to a variety of plants and animals that have been attuned to the harsh conditions. Some of these specializations include drought tolerance, water conservation, heat tolerance, camouflage, and nocturnal activity. Deserts also have unique geological features, such as sand dunes, salt flats, oases, and rock formations.

Deserts are important for many reasons. They provide natural resources, such as minerals, oil, and solar energy. They also influence the global climate by reflecting solar radiation and creating wind patterns. Deserts are also rich in cultural diversity and history, as many civilizations have emerged and thrived in these environments.

Characteristics of Deserts

Deserts are fascinating ecosystems that cover about one-third of the Earth's land surface. They are defined as areas that receive no more than 25 centimeters (10 inches) of precipitation a year. Deserts are home to a variety of plants and animals that have adapted to the harsh and dry conditions. Below are some of the general characteristics of deserts and how they differ from other biomes.

            Aridity

The most obvious characteristic of deserts is their lack of water. Aridity is a measure of how dry an area is, based on the ratio of precipitation to potential evaporation. Potential evaporation is the amount of water that would evaporate from the surface if it were available. Deserts have a very low aridity index, meaning that they receive much less precipitation than they could potentially lose to evaporation. Aridity can be caused by various factors, such as distance from the ocean, rain shadow effect, cold ocean currents, or high atmospheric pressure.

            Temperature

Deserts are often associated with high temperatures, but this is not always the case. Temperature in deserts varies widely depending on the location, season, and time of day. Some deserts are hot and dry, such as the Sahara and the Arabian deserts, where daytime temperatures can reach up to 54°C (130°F) in summer. Other deserts are semi-arid, coastal, or cold, such as the Great Basin and the Gobi deserts, where winter temperatures can drop below freezing. Deserts also experience large diurnal temperature ranges, meaning that there is a big difference between day and night temperatures. This is because the dry air and sparse cloud cover allow more solar radiation to reach the ground during the day and more heat to escape to space at night.

            Humidity

Humidity is a measure of how much water vapor is in the air. Deserts have very low humidity levels, usually below 30%. Low humidity means that the air can hold more water vapor before it becomes saturated. This makes it harder for clouds to form and for precipitation to occur. Low humidity also affects the living organisms in deserts, as they lose more water through evaporation from their bodies and need to conserve water in various ways.

            Precipitation

Precipitation is any form of water that falls from the sky, such as rain, snow, hail, or fog. Deserts receive very little precipitation, usually less than 25 centimeters (10 inches) per year. However, precipitation in deserts is not evenly distributed throughout the year or across different regions. Some deserts may have seasonal rains, such as the monsoon rains in the Thar desert or the winter rains in the Atacama desert. Some deserts may have occasional flash floods, such as the Mojave desert or the Namib desert. Some deserts may have fog or dew, such as the coastal deserts along the Pacific and Atlantic oceans.

            Drought

Drought is a prolonged period of abnormally low precipitation that causes a shortage of water for human and natural systems. Droughts can occur in any biome, but they are more frequent and severe in deserts. Droughts can have negative impacts on agriculture, wildlife, health, economy, and society. Droughts can be classified into four types: meteorological drought (lack of precipitation), hydrological drought (low water levels in rivers, lakes, reservoirs), agricultural drought (low soil moisture), and socioeconomic drought (insufficient water supply for human needs).

            Wind

Wind is the movement of air caused by differences in air pressure. Wind can affect the climate and landscape of deserts in various ways. Wind can increase evaporation and reduce humidity by carrying away water vapor from the surface. Wind can also erode and transport sand and dust particles, creating landforms such as dunes, yardangs, and loess deposits. Wind can also influence the distribution of seeds, pollen, and spores of plants and fungi.

            Vegetation

Vegetation is the term used to describe the plants that grow in a certain area. Vegetation in deserts is sparse and adapted to survive in dry conditions. Some of the common specializations of desert plants are:

        - Reduced leaf size: to reduce water loss through transpiration

        - Thick cuticle: to prevent water loss through evaporation

        - Spines or hairs: to reflect sunlight and reduce heat absorption

        - Deep or wide roots: to access water from underground or nearby sources

        - Succulence: to store water in stems or leaves

      - CAM *** (Crassulacean acid Metabolism) photosynthesis: to fix carbon dioxide at night and reduce.

***CAM photosynthesis is a type of carbon fixation that some plants use in dry environments. It allows them to take in carbon dioxide at night and store it as an acid, which they can use for photosynthesis during the day without losing water. 

Location of Deserts:

Deserts are where they are in the world because of the global atmospheric circulation, which creates zones of high and low pressure that affect the rainfall patterns of different regions. Most of the world's deserts are located near 30 degrees north and south of the equator, where the air is dry and sinks due to atmospheric circulation patterns. However, this is not the only factor that determines where deserts are located. Other factors include mountain ranges, ocean currents, and climate change. Some deserts are also found on the western coasts of continents, where cold ocean currents create dry winds that blow over the land. 

Classification of Deserts:

Deserts are regions that receive very little rainfall and have a high evaporation rate. They cover about one-fifth of the Earth's land surface and can have different climates, vegetation and wildlife. There are several ways to classify deserts based on their geographical location, dominant weather pattern, temperature and moisture.

The most common classification system divides deserts into five types: subtropical, coastal, rain shadow, interior and polar. 

•  Subtropical deserts are located in the tropics, where hot and dry air masses create high pressure zones that prevent cloud formation and precipitation. Examples of subtropical deserts are the Sahara, the Arabian and the Kalahari.
•  Coastal deserts are found along the western coasts of continents, where cold ocean currents create stable and dry air masses that move inland. Examples of coastal deserts are the Atacama, the Namib and the Baja California.
•  Rain shadow deserts are formed on the leeward side of mountain ranges, where moist air masses lose their moisture as they rise and cool over the mountains, leaving dry air to descend on the other side. Examples of rain shadow deserts are the Great Basin, the Gobi and the Patagonia.
•  Interior deserts are located far from any source of moisture, such as oceans or large lakes. They have low rainfall and high temperature variations between day and night. Examples of interior deserts are the Taklamakan, the Karakum and the Great Victoria.
•  Polar deserts are found in the polar regions, where low temperatures and high winds create dry and frozen conditions. They have very little precipitation, mostly in the form of snow or ice. Examples of polar deserts are Antarctica and Greenland.

Desert Landforms:

Deserts have diverse and unique landforms that are shaped by wind and water erosion, deposition, and weathering. Some of the common desert landforms are:

- Dunes: mounds or ridges of sand that are formed by wind blowing over loose sand. Dunes can have different shapes and sizes depending on the wind direction, speed, and sand supply. Some examples of dune types are barchan, transverse, longitudinal, star, and parabolic dunes.

- Salt flats: large areas of land formed by the evaporation of ancient lakes. They are composed of crystallized salt, minerals, and clay, creating a smooth and reflective surface that stretches for miles.

- Playas: flat areas of clay or salt that are formed by the evaporation of water from temporary lakes or ponds. Playas can be dry or wet depending on the season and rainfall. They often have cracks or polygons on their surface due to contraction and expansion.

- Alluvial fans: cone-shaped deposits of sediment that are formed by streams flowing from mountains to plains. Alluvial fans can be active or inactive depending on the water availability and erosion rate. They often have braided channels or deltas on their surface.

- Mesas and buttes: flat-topped hills or mountains that are formed by erosion of horizontal layers of rock. Mesas are larger than buttes, which are larger than pinnacles or chimneys. They often have steep cliffs or escarpments on their sides.

- Arches and bridges: natural openings or spans in rock that are formed by erosion of softer layers or joints. Arches have no support below them, while bridges have support on both sides. They often have delicate or spectacular shapes.

- Desert varnish: is a thin coating of minerals and organic matter that forms on exposed rocks in arid regions. It is composed mainly of iron and manganese oxides, clay minerals, and sand grains. Desert varnish can have different colors, from red to black, depending on the chemical composition and environmental conditions. Desert varnish is a result of chemical and biological processes that occur over thousands of years on the rock surface.

- Desert Pavement: area is covered by a layer of closely packed rocks. Desert pavement is formed by a process called deflation, in which the finer particles of sand and dust are blown away, leaving behind the coarser and heavier rocks.

Desert Life:

Deserts are home to a variety of plants and animals that are specialized to survive in harsh conditions. Some of the specialization include:

- Drought tolerance: plants and animals can reduce water loss or store water in their tissues or organs. For example, cacti have thick stems with spines instead of leaves, camels have humps with fat reserves, and kangaroo rats have efficient kidneys that produce concentrated urine.

- Heat tolerance: plants and animals can regulate their body temperature or avoid heat stress by behavioral or physiological means. For example, succulents have waxy coatings or hairs that reflect sunlight, reptiles have scales or shells that insulate them from heat, and rodents have burrows or nocturnal habits that keep them cool.

- Food scarcity: plants and animals can obtain nutrients from limited or specialized sources or store food for future use. For example, acacia trees have symbiotic relationships with ants that protect them from herbivores, insects have mouthparts or digestive enzymes that allow them to feed on sap or nectar, and foxes have caches or dens where they store food.

Deserts are also rich in cultural diversity and human history. Many civilizations have thrived in deserts by developing irrigation systems, trade networks, art forms, religions, and technologies. Some examples of desert cultures are the Egyptians, the Bedouins, the Berbers, the Tuare.

Conclusion:

Deserts are arid regions that receive very little precipitation. They cover about one-fifth of the Earth's land surface and can be found on every continent.  There are 23 deserts in the world. Deserts have extreme temperatures, ranging from scorching hot to freezing cold.

Points to Ponder:

Are deserts of not much value or do they have vital importance for the planetary ecosystem?