Misplaced Pages

#796203

27-732: The Volga delta has grown significantly in the 20th century because of changes in the level of the Caspian Sea. In 1880, the delta had an area of 3,222 km (1,244 sq mi). Today the Volga Delta covers an area of 27,224 km (10,511 sq mi) and is approximately 160 km (100 mi) across. It has a classical "delta pattern". The delta lies in the arid climate zone, characterized by very little rainfall. The region receives less than one inch of rainfall in January and July in normal years. Strong winds often sweep across

54-773: A few instances), dry summers, though summers are not typically as hot as hot desert climates. Unlike hot desert climates, cold desert climates tend to feature cold, dry winters. Snow tends to be rare in regions with this climate. The Gobi Desert in northern China and Mongolia is one example of a cold desert. Though hot in the summer, it shares the freezing winters of the rest of Inner Asia . Summers in South America's Atacama Desert are mild, with only slight temperature variations between seasons. Cold desert climates are typically found at higher altitudes than hot desert climates and are usually drier than hot desert climates. Cold desert climates are typically located in temperate zones in

81-566: Is determined. The precipitation threshold (in millimetres) involves first multiplying the average annual temperature in °C by 20, then adding 280 if 70% or more of the total precipitation is in the high-sun summer half of the year (April through September in the Northern Hemisphere , or October through March in the Southern), or 140 if 30–70% of the total precipitation is received during the applicable period, or 0 if less than 30% of

108-554: Is largely the result of the general circulation of the atmosphere . The latter does change significantly over time through climate change . For example, temperature increase by 1.5–2.1 percent across the Nile Basin over the next 30–40 years could change the region from semi-arid to arid, significantly reducing the land usable for agriculture . In addition, changes in land use can increase demands on soil water and thereby increase aridity. This climatology -related article

135-419: Is now discredited, and now they are thought to have arisen either underwater or through river flow. The second zone, in the delta proper, generally has very little relief (usually less than one metre), and is the site of active and abandoned water channels, small dunes and algal flats. The third zone is composed of a broad platform extending up to 60 km (37 mi) offshore, and is the submarine part of

162-550: Is seen in sections of Africa and Arabia . During colder periods of the year, night-time temperatures can drop to freezing or below due to the exceptional radiation loss under the clear skies. However, temperatures rarely drop far below freezing under the hot subtype. Hot desert climates can be found in the deserts of North Africa such as the wide Sahara Desert , the Libyan Desert or the Nubian Desert ; deserts of

189-444: Is the condition of a region that severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic . Most arid climates are located in the subtropics ; these regions include parts of Africa , Asia , South America , North America , and Australia . The distribution of aridity at any time

216-403: Is used as an isotherm so that a location with a BW type climate with the appropriate temperature above this isotherm is classified as "hot arid subtype" ( BW h ), and a location with the appropriate temperature below the isotherm is classified as "cold arid subtype" ( BW k ). Most desert/arid climates receive between 25 and 200 mm (1 and 8 in) of rainfall annually, although some of

243-953: The Horn of Africa such as the Danakil Desert or the Grand Bara Desert ; deserts of Southern Africa such as the Namib Desert or the Kalahari Desert ; deserts of West Asia such as the Arabian Desert , or the Syrian Desert ; deserts of South Asia such as Dasht-e Lut and Dasht-e Kavir of Iran or the Thar Desert of India and Pakistan; deserts of the United States and Mexico such as

270-721: The Indian Subcontinent , southwestern Africa, interior Australia, the Southwestern United States , northern Mexico , sections of southeastern Spain , the coast of Peru , and Chile . This makes hot deserts present in every continent except Antarctica. At the time of high sun (summer), scorching, desiccating heat prevails. Hot-month average temperatures are normally between 29 and 35 °C (84 and 95 °F), and midday readings of 43–46 °C (109–115 °F) are common. The world's absolute heat records, over 50 °C (122 °F), are generally in

297-804: The Mojave Desert , the Sonoran Desert or the Chihuahuan Desert ; deserts of Australia such as the Simpson Desert or the Great Victoria Desert and many other regions. In Europe , the hot desert climate can only be found on southeastern coast of Spain as well as small inland parts of southeastern, especially parts of the Tabernas Desert . Hot deserts are lands of extremes: most of them are among

SECTION 10

#1732766302797

324-534: The Sahara Desert such as Kufra , Libya , record an even drier 0.86 mm (0.034 in) of rainfall annually. The official weather station in Death Valley , United States reports 60 mm (2.4 in) annually, but in 40 months between 1931 and 1934 a total of just 16 mm (0.63 in) of rainfall was measured. To determine whether a location has an arid climate, the precipitation threshold

351-585: The algal blooms that grow on the surface of the sea, allowing them to grow larger. 46°43′59″N 47°51′00″E  /  46.733°N 47.850°E  / 46.733; 47.850 Arid climate The desert climate or arid climate (in the Köppen climate classification BWh and BWk ) is a dry climate sub-type in which there is a severe excess of evaporation over precipitation . The typically bald, rocky, or sandy surfaces in desert climates are dry and hold little moisture, quickly evaporating

378-652: The 30s and 40s latitudes, usually in the leeward rain shadow of high mountains, restricting precipitation from the westerly winds. An example of this is the Patagonian Desert in Argentina, bounded by the Andes ranges to its west. In the case of Central Asia, mountains restrict precipitation from the eastern monsoon . The Kyzyl Kum , Taklamakan and Katpana Desert deserts of Central Asia are other significant examples of BWk climates. The Ladakh region and

405-741: The Arctic and Antarctic regions receive very little precipitation during the year owing to the cold, dry air freezing most precipitation. Polar desert climates have desert-like features that occur in cold desert climates, including intermittent streams, hypersaline lakes, and extremely barren terrain in unglaciated areas such as the McMurdo Dry Valleys of Antarctica. These areas are generally classified as having polar climates because they have average summer temperatures below 10 °C (50 °F) even if they have some characteristics of extreme non-polar deserts. Dry climate Aridity

432-567: The Baer's mounds are depressions that fill with water and become either fresh or saline bays; the height from the bottom of a depression to the peak of its neighboring mound ranges from 10 to 15 m (30 to 50 ft). These depressions, called " ilmens " (from Russian through Finnish, "small lake," as in Russia's Lake Ilmen ), used to form part of the early, very deep river delta but gradually became separated from it. Because of their isolation from

459-504: The already little rainfall they receive. Covering 14.2% of Earth's land area, hot deserts are the second-most common type of climate on Earth after the Polar climate . There are two variations of a desert climate according to the Köppen climate classification : a hot desert climate ( BWh ), and a cold desert climate ( BWk ). To delineate "hot desert climates" from "cold desert climates", a mean annual temperature of 18 °C (64.4 °F)

486-994: The city of Leh in the Great Himalayas in India also have a cold desert climate. In North America, the cold desert climate occurs in the drier parts of the Great Basin Desert and the Bighorn Basin in Big Horn and Washakie County in Wyoming . The Hautes Plaines , located in the northeastern section of Morocco and in Algeria , is another prominent example of a cold desert climate. In Europe , this climate only occurs in some inland parts of southeastern Spain, such as in Lorca . Polar climate desert areas in

513-580: The delta and form linear dunes. Along the front of the delta, one will find muddy sand shoals, mudflats, and coquina banks. The changing level of the Caspian Sea has resulted in three distinct zones in the delta. The higher areas of the first zone are known as "Baer's mounds," named after researcher Karl Ernst von Baer who worked in this region. These mounds are linear ridges of clayey sands, ranging from 5 to 22 m (16 to 72 ft) in height, and averaging about 8 m (26 ft). They are between 0.4 and 10 km (0.2 and 6 mi) in length. Between

540-419: The delta plain has resulted in significant wetland loss. Between 1984 and 2001, the delta lost 277 km (107 sq mi) of wetlands , or an average of approximately 16 km (6.2 sq mi) per year, from natural and human-induced causes. The Volga discharges large amounts of industrial waste and sediment into the relatively shallow northern part of the Caspian Sea. The added fertilizers nourish

567-527: The delta region. The lotus has been adopted as the motif of the national flag of the neighbouring Kalmyks , since it is a venerated symbol in their Buddhist beliefs – they are the sole European people of Mongolian ( Oirat ) origin. The delta has been designated an Important Bird Area (IBA) by BirdLife International because it supports significant numbers of many waterbird species, including breeding squacco herons , great white egrets and Dalmatian pelicans . Industrial and agricultural modification to

SECTION 20

#1732766302797

594-432: The delta. The delta has been protected since the early 1900s, with one of the first Russian nature preserves ( Astrakhan Nature Reserve ) having been set up there in 1919. Much of its local fauna is considered endangered. The delta is a major staging area for many species of water birds, raptors and passerines . Although the delta is best known for its sturgeons , catfish and carp are also found in large numbers in

621-492: The fresh waters of the Volga, they are becoming increasingly saline. Together they form a "vast (more than 300 km (120 sq mi)) and extremely diverse area of western substeppe ilmens (WSI)" which, because of the varying degrees of wetness and salinization, house a wealth of flora and fauna. The origin of these mounds and ilmens is still debated: the early suggestion that they were formed by aeolian (wind) action

648-599: The hot deserts, where the heat potential can be the highest on the planet. This includes the record of 56.7 °C (134.1 °F) in Death Valley , which is currently considered the highest temperature recorded on Earth . Some deserts in the tropics consistently experience very high temperatures all year long, even during wintertime. These locations feature some of the highest annual average temperatures recorded on Earth, exceeding 30 °C (86 °F), up to nearly 35 °C (95 °F) in Dallol, Ethiopia . This last feature

675-444: The hottest, the driest, and the sunniest places on Earth because of nearly constant high pressure; the almost permanent removal of low-pressure systems, dynamic fronts, and atmospheric disturbances; sinking air motion; dry atmosphere near the surface and aloft; the exacerbated exposure to the sun where solar angles are always high makes this desert inhospitable to most species. Cold desert climates ( BWk ) usually feature hot (or warm in

702-549: The most consistently hot areas of Central Australia , the Sahel and Guajira Peninsula can be, due to extreme potential evapotranspiration , classed as arid with the annual rainfall as high as 430 millimetres or 17 inches. Although no part of Earth is known for certain to be rainless, in the Atacama Desert of northern Chile, the average annual rainfall over 17 years was only 5 millimetres (0.20 in). Some locations in

729-650: The total precipitation is so received there. If the area's annual precipitation is less than half the threshold (50%), it is classified as a BW (desert climate), while 50–100% of the threshold results in a semi-arid climate. Hot desert climates ( BWh ) are typically found under the subtropical ridge in the lower middle latitudes or the subtropics , often between 20° and 33° north and south latitudes. In these locations, stable descending air and high pressure aloft clear clouds and create hot, arid conditions with intense sunshine. Hot desert climates are found across vast areas of North Africa , West Asia , northwestern parts of

#796203