Fresh water is any occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, icebergs, ponds, rivers and underground water called groundwater. Fresh water is characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water is not the same as potable water. Much of the earth's fresh water is unsuitable for drinking without some treatment. Fresh water can become polluted by human activities or due to occurring processes, such as erosion. Water is critical to the survival of all living organisms; some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live. Fresh water can be defined as water with less than 500 parts per million of dissolved salts. Other sources give higher upper salinity limits for e.g. 1000 ppm or 3000 ppm. Fresh water habitats are classified as either lentic systems, which are the stillwaters including ponds, lakes and mires.
There is, in addition, a zone which bridges between groundwater and lotic systems, the hyporheic zone, which underlies many larger rivers and can contain more water than is seen in the open channel. It may be in direct contact with the underlying underground water; the majority of fresh water on Earth is in ice caps. The source of all fresh water is precipitation from the atmosphere, in the form of mist and snow. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled. In industrialized areas rain is acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of rivers. In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds.
This can give rise to elevated concentrations of sodium, chloride and sulfate as well as many other compounds in smaller concentrations. In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa. Saline water in oceans and saline groundwater make up about 97% of all the water on Earth. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers and snow, 0.5–0.75% as fresh groundwater and soil moisture, less than 0.01% of it as surface water in lakes and rivers. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the African Great Lakes, 22% in Lake Baikal in Russia, 21% in the North American Great Lakes, 14% in other lakes.
Swamps have most of the balance with only a small amount in rivers, most notably the Amazon River. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in ice sheets. Many areas suffer from lack of distribution such as deserts. Water is a critical issue for the survival of all living organisms; some can use salt water but many organisms including the great majority of higher plants and most mammals must have access to fresh water to live. Some terrestrial mammals desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, they have mechanisms to conserve water to the maximum degree. Fresh water creates a hypotonic environment for aquatic organisms; this is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted.
Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh water and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; the eel uses the hormone prolactin, while in salmon the hormone cortisol plays a key role during this process. Many sea birds have special glands at the base of the bill; the marine iguanas on the Galápagos Islands excrete excess salt through a nasal gland and they sneeze out a salty excretion. Freshwater molluscs include freshwater snails and freshwater bivalves. Freshwater crustaceans include crayfish. Freshwater biodiversity faces many threats; the World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014.
These declines continue to outpace
The Lake Katam is one of the larger lakes in Ounianga Kebir, a lake system in the Borkou-Ennedi-Tibesti Region in the north-east basin of Chad. These lakes are notable for their running in the north-south headlands, by the Trade wind are formed, they are the remnant of a much larger lake, that filled the basin during the so-called green Sahara-time, which lasted from about BC 10000-1500. Lake Yoa Lakes of Ounianga
Chad the Republic of Chad, is a landlocked country in north-central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south and Nigeria to the southwest, Niger to the west, it is the second-largest in Central Africa in terms of area. Chad has several regions: a desert zone in the north, an arid Sahelian belt in the centre and a more fertile Sudanian Savanna zone in the south. Lake Chad, after which the country is named, is the largest wetland in Chad and the second-largest in Africa; the capital N'Djamena is the largest city. Chad's official languages are French. Chad is home to over 200 different linguistic groups; the most popular religion of Chad is Islam, followed by Christianity. Beginning in the 7th millennium BC, human populations moved into the Chadian basin in great numbers. By the end of the 1st millennium AD, a series of states and empires had risen and fallen in Chad's Sahelian strip, each focused on controlling the trans-Saharan trade routes that passed through the region.
France incorporated it as part of French Equatorial Africa. In 1960, Chad obtained independence under the leadership of François Tombalbaye. Resentment towards his policies in the Muslim north culminated in the eruption of a long-lasting civil war in 1965. In 1979 the rebels put an end to the south's hegemony. However, the rebel commanders fought amongst themselves, he was overthrown in 1990 by his general Idriss Déby. Since 2003 the Darfur crisis in Sudan has spilt over the border and destabilised the nation, with hundreds of thousands of Sudanese refugees living in and around camps in eastern Chad. An uneven inclusion into the global political economy as a site for colonial resource extraction, a global economic system that does not promote nor encourage the development of Chadian industrialization, the failure to support local agricultural production has meant that the majority of Chadians live in daily uncertainty and hunger. While many political parties are active, power lies in the hands of President Déby and his political party, the Patriotic Salvation Movement.
Chad remains plagued by recurrent attempted coups d'état. Since 2003, crude oil has become the country's primary source of export earnings, superseding the traditional cotton industry. In the 7th millennium BC, ecological conditions in the northern half of Chadian territory favored human settlement, the region experienced a strong population increase; some of the most important African archaeological sites are found in Chad in the Borkou-Ennedi-Tibesti Region. For more than 2,000 years, the Chadian Basin has been inhabited by agricultural and sedentary people; the region became a crossroads of civilizations. The earliest of these were the legendary Sao, descendants of the Hyksos who conquered Ancient Egypt known for skills in designing weapons and artifacts, they are known for their oral histories. After a century of rule, the Sao fell to the Kanem Empire, the first and longest-lasting of the empires that developed in Chad's Sahelian strip by the end of the 1st millennium AD. Two other states in the region, Sultanate of Bagirmi and Wadai Empire emerged in the 16th and 17th centuries.
The power of Kanem and its successors was based on control of the trans-Saharan trade routes that passed through the region. These states, at least tacitly Muslim, never extended their control to the southern grasslands except to raid for slaves. In Kanem, about a third of the population were slaves. French colonial expansion led to the creation of the Territoire Militaire des Pays et Protectorats du Tchad in 1900. By 1920, France had secured full control of the colony and incorporated it as part of French Equatorial Africa. French rule in Chad was characterised by an absence of policies to unify the territory and sluggish modernisation compared to other French colonies; the French viewed the colony as an unimportant source of untrained labour and raw cotton. The colonial administration in Chad was critically understaffed and had to rely on the dregs of the French civil service. Only the Sara of the south was governed effectively; the educational system was affected by this neglect. After World War II, France granted Chad the status of overseas territory and its inhabitants the right to elect representatives to the National Assembly and a Chadian assembly.
The largest political party was the Chadian Progressive Party, based in the southern half of the colony. Chad was granted independence on 11 August 1960 with the PPT's leader, Sara François Tombalbaye, as its first president. Two years Tombalbaye banned opposition parties and established a one-party system. Tombalbaye's autocratic rule and insensitive mismanagement exacerbated inter-ethnic tensions. In 1965, Muslims in the north, led by the National Liberation Front of Chad, began a civil war. Tombalbaye was overthrown and killed in 1975. In 1979 the rebel factions led by Hissène Habré took the capital, all central authority in the country collapsed. Armed factions, many from the north's rebellion, contended for power; the disintegration of Chad caused the collapse of France's position in the country. Libya moved to fill the power vacuum and became involved in Chad
A drought or drouth is a natural disaster of below-average precipitation in a given region, resulting in prolonged shortages in the water supply, whether atmospheric, surface water or ground water. A drought may be declared after as few as 15 days, it can have a substantial impact on the ecosystem and agriculture of the affected region and harm to the local economy. Annual dry seasons in the tropics increase the chances of a drought developing and subsequent bush fires. Periods of heat can worsen drought conditions by hastening evaporation of water vapour. Many plant species, such as those in the family Cactaceae, have drought tolerance adaptations like reduced leaf area and waxy cuticles to enhance their ability to tolerate drought; some others survive dry periods as buried seeds. Semi-permanent drought produces arid biomes such as grasslands. Prolonged droughts have caused humanitarian crisis. Most arid ecosystems have inherently low productivity; the most prolonged drought in the world in recorded history occurred in the Atacama Desert in Chile.
Mechanisms of producing precipitation include convective and orographic rainfall. Convective processes involve strong vertical motions that can cause the overturning of the atmosphere in that location within an hour and cause heavy precipitation, while stratiform processes involve weaker upward motions and less intense precipitation over a longer duration. Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice. Droughts occur in areas where normal levels of rainfall are, in themselves, low. If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought can be triggered by a high level of reflected sunlight and above average prevalence of high pressure systems, winds carrying continental, rather than oceanic air masses, ridges of high pressure areas aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region.
Once a region is within drought, feedback mechanisms such as local arid air, hot conditions which can promote warm core ridging, minimal evapotranspiration can worsen drought conditions. Within the tropics, distinct and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough; the dry season increases drought occurrence, is characterized by its low humidity, with watering holes and rivers drying up. Because of the lack of these watering holes, many grazing animals are forced to migrate due to the lack of water in search of more fertile lands. Examples of such animals are zebras and wildebeest; because of the lack of water in the plants, bushfires are common. Since water vapor becomes more energetic with increasing temperature, more water vapor is required to increase relative humidity values to 100% at higher temperatures. Periods of warmth quicken the pace of fruit and vegetable production, increase evaporation and transpiration from plants, worsen drought conditions.
Drier and hotter weather occurs in parts of the Amazon River Basin and Central America during El Niño events. Winters during the El Niño are warmer and drier than average conditions in the Northwest, northern Midwest, northern Mideast United States, so those regions experience reduced snowfalls. Conditions are drier than normal from December to February in south-central Africa in Zambia, Zimbabwe and Botswana. Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing bush fires, worsening haze, decreasing air quality dramatically. Drier-than-normal conditions are in general observed in Queensland, inland Victoria, inland New South Wales, eastern Tasmania from June to August; as warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it causes extensive drought in the western Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February.
The years 2005 had the next driest Februaries, when 8.4 mm of rain fell. Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation and erosion adversely impact the ability of the land to capture and hold water. In arid climates, the main source of erosion is wind. Erosion can be the result of material movement by the wind; the wind can cause small particles to be therefore moved to another region. Suspended particles within the wind may impact on solid objects causing erosion by abrasion. Wind erosion occurs in areas with little or no vegetation in areas where there is insufficient rainfall to support vegetation. Loess is a homogeneous nonstratified, friable coherent calcareous, fine-grained, pale yellow or buff, windblown sediment, it occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess stands in either steep or vertical faces. Loess tends to develop into rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world.
Loess deposits are geologically unstable by nature, will erode readily. Therefore, windbreaks are planted by farmers to reduce the wind erosion of loess. Wind erosion
Lake Chad is a large, endorheic lake in Africa, which has varied in size over the centuries. According to the Global Resource Information Database of the United Nations Environment Programme, it shrank by as much as 95% from about 1963 to 1998, but "the 2007 image shows significant improvement over previous years." Lake Chad is economically important, providing water to more than 30 million people living in the four countries surrounding it on the edge of the Sahara. It is the largest lake in the Chad Basin. Lake Chad is a freshwater lake located in the Sahelian zone of west-central Africa, it is located in the interior basin which used to be occupied by a much larger ancient sea sometimes called Mega Chad. The lake is ranked as one of the largest lakes in Africa. However, its surface area varies by season and as well as from year to year. Lake Chad is in the far west of Chad, bordering on northeastern Nigeria; the Chari River, fed by its tributary the Logone, provides over 90% of the lake's water, with a small amount coming from the Yobe River in Nigeria/Niger.
Despite high levels of evaporation, the lake is fresh water. Over half of the lake's area is taken up by its many small islands and mud banks, a belt of swampland across the middle divides the northern and southern halves; the shorelines are composed of marshes. Because Lake Chad is shallow—only 10.5 metres at its deepest—its area is sensitive to small changes in average depth, it shows seasonal fluctuations in size. Lake Chad has no apparent outlet; the climate is dry most of the year, with moderate rainfall from July through September. Lake Chad gave its name to the country of Chad; the name Chad is a local word meaning "large expanse of water", in other words, a "lake". Lake Chad is the remnant of a former inland sea, paleolake Mega-Chad, which existed during the African humid period. At its largest, sometime before 5000 BC, Lake Mega-Chad was the largest of four Saharan paleolakes, is estimated to have covered an area of 1,000,000 km2, larger than the Caspian Sea is today, may have extended as far northeast as within 100 km of Faya-Largeau.
At its largest extent the river Mayo Kébbi represented the outlet of the paleolake Mega-Chad, connecting it to the Niger River and the Atlantic. The presence of African manatees in the inflows of Lake Chad is an evidence of that history. Romans reached the lake in the first century of their empire. Indeed, during the time of Augustus Lake Chad was still a huge lake and two Roman expeditions were performed in order to reach it: Septimius Flaccus and Julius Maternus reached the "lake of hippopotamus", they passed near the Tibesti mountains. Both expeditions passed through the territory of the Garamantes, were able to leave a small garrison on the "lake of hippopotamus and rhinoceros" after three months of travel in desert lands. Lake Chad was first surveyed from shore by Europeans in 1823, it was considered to be one of the largest lakes in the world then. In 1851, a party including the German explorer Heinrich Barth carried a boat overland from Tripoli across the Sahara Desert by camel and made the first European waterborne survey.
British expedition leader James Richardson died just days before reaching the lake. In Winston Churchill's book The River War: An Account of the Reconquest of the Sudan, published in 1899, he mentions the shrinking of Lake Chad, he writes: Altogether France has enough to occupy her in Central Africa for some time to come: and when the long task is finished, the conquered regions are not to be of great value. They include the desert of the Great Sahara and wide expanses of profitless scrub or marsh. Only one important river, the Shari, flows through them, never reaches the sea: and Lake Chad, into which the Shari flows, appears to be leaking through some subterranean exit, is changing from a lake into an immense swamp. Lake Chad has shrunk since the 1960s, when its shoreline had an elevation of about 286 metres above sea level and it had an area of more than 26,000 square kilometres, making its surface the fourth largest in Africa. An increased demand on the lake's water from the local population has accelerated its shrinkage over the past 40 years.
The size of Lake Chad varies seasonally with the flooding of the wetlands areas. In 1983, Lake Chad was reported to have covered 10,000 to 25,000 km2, had a maximum depth of 11 metres, a volume of 72 km3. By 2000, its extent had fallen to less than 1,500 km2. A 2001 study published in the Journal of Geophysical Research blamed the lake's retreat on overgrazing in the area surrounding the lake, causing desertification and a decline in vegetation; the United Nations Environment Programme and the Lake Chad Basin Commission concur that at least half of the lake's decrease is attributable to shifting climate patterns. UNEP blames human water use, such as inefficient damming and irrigation methods, for the rest of the shrinkage; as late as December 2014, Lake Chad was still sufficient in size and volume such that boats could capsize or sink. The European Space Agency has presented data showing an actual increase in lake extent of Lake Chad between the years of 1985 to 2011. Referring to the floodplain as a lake may be misleading, as less than half of Lake Chad is covered by water through an entire year.
The remaining sections are considered as wetla
N’Djamena is the capital and largest city of Chad. A port on the Chari River, near the confluence with the Logone River, it directly faces the Cameroonian town of Kousséri, to which the city is connected by a bridge, it is a special statute region, divided into 10 districts or arrondissements. It is a regional market for livestock, salt and grains. Meat and cotton processing are the chief industries, the city continues to serve as the center of economic activity in Chad. N’Djamena was founded as Fort-Lamy by French commander Émile Gentil on May 29, 1900, named after Amédée-François Lamy, an army officer, killed in the Battle of Kousséri a few days earlier, it became the capital of the region and nation. During the Second World War, the French relied upon the city's airport to move supplies. On 21 January 1942, a lone German He 111 of the Sonderkommando Blaich bombed the airfield at Fort-Lamy, destroying oil supplies and ten aircraft. Fort-Lamy received its first bank branch in 1950, when the Bank of West Africa opened a branch there.
On April 6, 1973, the President François Tombalbaye changed its name to N’Djamena as part of his authenticité program of Africanization. The city was occupied by Libya during the 1980–81 Libyan intervention as part of the Chadian–Libyan conflict, the associated Transitional Government of National Unity; the city was destroyed during the Chadian Civil War, in 1979 and again in 1980. In these years all of the population fled the town, searching for refuge on the opposite bank of the Chari River in Cameroon, next to the city of Kousseri; the residents did not return until 1981–82, after the end of the clashes. Until 1984, facilities and services were subject to strict rationing, schools remained closed; the period of turmoil in the city was started by the abortive coup attempted by the northerner Prime Minister Hissène Habré against the southerner President Félix Malloum: while Malloum and the national army loyal to him were defeated, the intervention in the battle of other northern factions rival to that of Habré complicated the situation.
A temporary truce was reached in 1979 through international mediation, establishing the warlord Goukouni Oueddei as head of a government of national unity with his rival Habré as Defense Minister. The intense rivalry between Goukouni and Habré caused the eruption of new clashes in the city in 1980; the tug-of-war reached a conclusion after many months only when Goukouni asked for the intervention of the Libyans, whose tanks overwhelmed Habré's defenses in the capital. Following differences between Goukouni and Muammar Gaddafi and international disapproval of Libyan intervention, the Libyan troops left the capital and Chad in 1981; this opened the door to Habré, who marched on N’Djamena, occupying the city with little resistance in 1982 and installing himself as the new president. He was dislodged in a similar fashion in 1990 by a former general of his, Idriss Déby, as of 2016 the head of state of Chad; the city had only 9,976 inhabitants in 1937, but a decade in 1947, the population had doubled to 18,435.
In 1968, after independence, the population reached 126,483. In 1993, it surpassed half a million with 529,555. A good deal of this growth has been due to refugees fleeing into N’Djamena for security, although many people fled N’Djamena depending on the political situation. On April 13, 2006, a rebel United Front for Democratic Change attack on the city was defeated in the Battle of N’Djamena; the city was once again attacked on February 2008, by UFDD and RFC rebels. In N’Djamena, only about twenty- six percent of the area is urbanized. Most residents of Chad live in the capital city, N’Djamena, or the Logone Occidental Region just south of the capital. Just about half of the population is under the age of fifteen. Of these people, it is a uniform divide of females. While the division between genders is the divide among ethnic groups and religion are different. A variety of religions are with a clear Islamic predominance; the main ethnic groups are: Daza, Chadian Arabs, Ngambaye, Kanembu, Kanuri, Kuka and Barma.
N'Djamena's primary economic source is agricultural work. About 80% of the population within N'Djamena works within farming-based industries, including cultivation of crops and growing livestock; the economy in N'Djamena is therefore totally reliant on good weather, making the economy struggle in years with low rainfall. N'Djamena receives financial aid from the World Bank, as well as the African Development Bank. There is a high demand for skilled laborers within N'Djamena to work for oil and gas sectors, as well as laborers for foreign non-governmental organizations, medical services, English teaching. Residents of N'Djamena are liable to pay tax up to a maximum amount of 60% of all net income. N'Djamena is located at 12 ° 6 ′ 47 ″ N 15 ° 2 ′ 57 ″ E, on the confluence of the Logone rivers. While an administrative center, the city includes the Nassara Strip commercial centre and residential areas, such as Mbololo, Paris Congo and Moursal; the main commercial avenue of the city is the Avenue Charles de Gaulle.
N'Djamena has a semi-arid climate with a lengthy dry season. Despite the fact that the city receives on average 510 mm of rain annuall