Hot & Mid-Latitude Deserts
Desert regions are characterised by very little rainfall and scanty vegetation. The length of
Hot & Mid-Latitude Deserts
They can be of two types:
- hot deserts - like Saharan desert
- mid-latitude deserts - like Gobi desert.
Hot deserts - distribution
- Important hot deserts of the world are situated on the western edges of the continents between latitudes 15 to 30 degrees north and south.
- Sahara desert is the largest of hot deserts, covering an area of 3.5 million square miles. Other prominent hot deserts include the Great Australian Desert, Arabian desert, Kalahari desert, Thar desert etc.
- Hot deserts are also found in the Americas. In North America, they are known by the names of Mohave, Sonoran, Californian, and Mexican deserts. They extend between
USAand Mexico. In South America, the Atacama desert, or the Peruvian desert is located.
Hot deserts - Temperature
- These deserts are some of the hottest places on earth and have high temperatures all around the year.
- They do not have a distinct cold weather season.
- The average summer temperatures are always above 30 degrees centigrade.
- The hottest temperature to be recorded was in Libya in 1922. The temperatures rose as high as 57 degrees centigrade.
- Cloudless skies, intense insolation, dry air, and a rapid rate of evaporation are the reasons for such high temperatures.
- However, coastal areas of these deserts have a relatively moderate climate due to the moderating influence of seas. The cooling effect of cold currents also reduces the mean temperatures experienced in this region.
- The interior regions experience extreme temperatures - hot summers and cold winters.
- The diurnal temperature range is very high. Intense solar radiation during the day coupled with dry air and cloudless skies cause the temperature to rise with the sun.
- However, as soon as the sun sets, the mercury drops below the mean temperature due to continuous loss of heat by radiation coupled with the absence of cloud cover that could retain the heat.
- The average diurnal range of temperatures is around 14 to 25 degrees centigrade.
- During winter nights, frost is a common occurrence
Hot deserts - Precipitation
- Average annual precipitation in these regions is not more than 25 cm.
- Since these deserts are located within the Sub-Tropical High-Pressure Belts, also known as the Horse Latitudes, where the air masses are descending, conditions are not favourable for the formation of clouds which can cause precipitation.
- The prevailing winds in these regions are the Trade Winds which blow off-shore and do not allow any moisture-laden winds to blow over these regions from the sea.
- Westerlies which are on-shore do not blow over the desert regions, reducing the chances of any precipitation.
- The winds that blow over the deserts come from colder regions and their relative humidity is lowered as they blow over the desert. This reduces the possibility of condensation of water vapour, and hence any precipitation.
- The relative humidity decreases from 60
percentin the coastal areas to less than 30 percentin the interiors. This increases the rate of evaporation and reduces any chance of precipitation, making these deserts regions of permanent drought.
- The cold currents which flow along the west coasts of the continents have a desiccating effect on these deserts. Any moisture-laden winds blowing from the sea get condensed over the cold currents into mist or fog, and only drier winds blow over the deserts.
convectionalrainfall occurs in these regions in the form of violent thunderstorms for shorter durations. These sudden downpours often have disastrous consequences in the form of landslides.
- Atacama desert is the driest region in the world with
an annualprecipitation of less than 2 cm.
Mid-Latitude deserts - distribution
- These desert are often situated on plateaux and are a part of continental interiors.
- They include Gobi desert, Turkestan desert, Patagonian desert etc.
- In India, Ladakh desert falls under this category.
Mid-latitude deserts - climate
- In many ways, the climatic conditions of these deserts are similar to those of the hot deserts.
- Since these deserts lie at far away locations from the coast or are blocked by high mountains surrounding them, they are cut off from the moisture-laden winds blowing from the seas.
- Average annual precipitation does not exceed 25 cm.
- However, depression may penetrate into these deserts occasionally in Asia, bringing light rainfall in winters. Convectional rainfall can happen during the summers.
- These regions have a very range of annual temperatures, greater than that of hot deserts. The reason behind such extreme temperatures is Continentality - a phenomenon associated with landmasses which are at great distances from the coast.
- Winters experience freezing temperatures and very strong cold winds blow over these regions. Ice thaws during the summers sometimes causing floods at many places.
- All deserts have some form of vegetation such as grass, scrub, weeds, etc.
- Though they may not appear green all the time, they lie dormant waiting for the rains which are irregular.
- The most common type of vegetation that is found in both hot and mid-latitude deserts is the xerophytic or drought-resistant scrub.
- Important species of this type include the bulbous cacti, long-rooted wiry grasses, thorny bushes, and dwarf acacia.
- In a few regions where there is abundant groundwater, clusters of date palms can be found, especially in the hot deserts.
- Vegetation that survives in these regions is of a special variety, which is adapted to intense aridity.
- Soils are deficient in humus due to the absence of moisture which slows down the rate of decomposition of organic matter.
- The shrub vegetation found in these deserts
havea well-developed system of long roots which grow in search of groundwater. They have few or no leaves, and their foliage is hairy, waxy, or needle-shaped in order to minimise the loss of water through transpiration.
- The seeds of these plants have special mechanisms to protect themselves when they lie dormant, in the form of thick, tough outer surfaces. As soon as they are moistened by the rain, they germinate.
Life in the deserts
Despite their inhospitable conditions, different types of human settlements have come up in these deserts
- Primitive hunters and gatherers: They are primitive tribes who do not cultivate any crops, or domesticate any animals. They include the Bushmen of the Kalahari desert, Bindibu or the Aborigines of Australia.
- Nomadic herdsmen: They pursue a livestock economy, wandering through the deserts along with their herds in search of water and green pastures. They include Bedouins of Arabia, the Tuaregs of Sahara, the Mongols of Gobi desert.
- Settled cultivators: They have survived close to rivers such as the Nile in Egypt, Indus in Pakistan, Colorado in the USA, and Tigris-Euphrates in Iraq. They cultivate crops like wheat, barley, sugarcane, fruits and vegetables
- Mining settlers: Prominent among these include the gold mines in Australia, Diamond mines in Kalahari, Copper mines in Chile, Silver mines in Mexico, Oil in the Persian Gulf countries.