what are the drought? how are they caused
Answers
Answer:A drought or drouth is an event of prolonged shortages in the water supply, whether atmospheric (below-average precipitation), surface water or ground water. A drought can last for months or years, or may be declared after as few as 15 days.[1] It can have a substantial impact on the ecosystem and agriculture of the affected region[2] and harm to the local economy.[3] Annual dry seasons in the tropics significantly increase the chances of a drought developing and subsequent bush fires. Periods of heat can significantly worsen drought conditions by hastening evaporation of water vapour.
Drought is a recurring feature of the climate in most parts of the world.
Many plant species, such as those in the family Cactaceae (or cacti), 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 deserts and grasslands.[4] Prolonged droughts have caused mass migrations and humanitarian crisis. Most arid ecosystems have inherently low productivity. The most prolonged drought ever in the world in recorded history occurred in the Atacama Desert in Chile (400 Years).[5]
Drought affect food production and human society, so they are considered a disaster, of natural, supernatural or human cause (which itself could be supernatural causes, malediction, sin, ...). It is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the Biblical story of Joseph's arrival in and the later Exodus from Ancient Egypt.[6] Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon,[7] as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.[8] Rituals exist to prevent or avert drought, rainmaking could go from dances to scapegoating to human sacrifices. Nowadays, those ancient practices are for the most part relegated to folklore and replaced by more rational water management.
Green Chemistry provides a unique forum for the publication of innovative research on the development of alternative green and sustainable technologies.
The scope of Green Chemistry is based on, but not limited to, the definition proposed by Anastas and Warner (Green Chemistry: Theory and Practice, P T Anastas and J C Warner, Oxford University Press, Oxford, 1998). Green chemistry is the utilisation of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture and application of chemical products.
Causes of Drought
Rainfall or Precipitation Deficiency
Droughts take place whenever there is prolonged periods of rainfall deficiency for a season or more and usually when there is a lack of anticipated rainfall or precipitation. When a region goes for long periods without any rain, especially for more than a season, then the situation leads to dry conditions and water deficiency which qualify as drought.
Farmers, for instance, plant in expectation of rain and so when it doesn’t rain as expected, drought conditions are experienced. In such cases, it is frequently termed as agricultural drought.
Human Causes
Human activities play a relatively significant role in the management of the water cycle. Human acts such as deforestation, construction, and agriculture negatively impact the water cycle. Trees and vegetation cover are essential for the water cycle as it helps to limit evaporation, stores water, and attracts rainfall.
In this sense, deforestation – clearing vegetation cover and cutting down trees increases evaporation and lessens the ability of the soil to hold water leading to increased susceptibility of desertification. Deforestation can also influence the occurrence of dry conditions since it reduces forest’s watershed potential. Construction and agricultural activities may as well reduce the overall supply quantity of water, resulting in dry spells.
Drying out of Surface Water Flow
Lakes, rivers, and streams are the primary suppliers of downstream surface waters in various geographical regions around the globe. In extremely hot seasons or because of certain human activities, these surface water flows may dry out downstream contributing to drought – meaning the demands for water supply become higher than the available water.
Irrigation systems and hydro-electric dams are some of the human activities that can significantly diminish the amount of water flowing downstream to other areas.
Global Warming
Human actions have contributed to more and more emissions of greenhouse gasses into the atmosphere thus resulting in the continued rise of the earth’s average temperatures. Consequently, evaporation and evapotranspiration levels have risen, and the higher temperatures have led to wildfires and extended dry spell periods. The global warming situation tends to exacerbate the drought conditions. Some of the worst droughts witnessed in sub-Saharan Africa have been associated with global warming and climate change.