Drought
Economic impacts of drought result due to negative disruptions to agriculture and livestock farming (causing food insecurity), forestry, public water supplies, maritime navigation (due to e.g.: lower water levels), electric power supply (by affecting hydropower systems) and impacts on human health.
The National Weather Service office of the NOAA defines drought as "a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area".
Within the tropics, distinct, wet and dry seasons emerge due to the movement of the Intertropical Convergence Zone or Monsoon trough.
[41] Periods of warmth quicken the pace of fruit and vegetable production,[42] increase evaporation and transpiration from plants,[43] and worsen drought conditions.
ENSO comprises two patterns of temperature anomalies in the central Pacific Ocean, known as La Niña and El Niño.
La Niña events are generally associated with drier and hotter conditions and further exacerbation of drought in California and the Southwestern United States, and to some extent the U.S. Southeast.
[45] Conversely, during El Niño events, drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America.
Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing bush fires, worsening haze, and decreasing air quality dramatically.
[53] Human activity can directly trigger exacerbating factors such as over-farming, excessive irrigation,[56] deforestation, and erosion adversely impact the ability of the land to capture and hold water.
[59] Drought is one of the most complex and major natural hazards, and it has devastating impacts on the environment, economy, water resources, agriculture, and society worldwide.
Environmental effects of droughts include: lower surface and subterranean water-levels, lower flow-levels (with a decrease below the minimum leading to direct danger for amphibian life), increased pollution of surface water, the drying out of wetlands, more and larger wildfires, higher deflation intensity, loss of biodiversity, worse health of trees and the appearance of pests and dendroid diseases.
Drought in combination with high levels of grazing pressure can function as the tipping point for an ecosystem, causing woody encroachment.
Drought stress impairs mitosis and cell elongation via loss of turgor pressure which results in poor growth.
[72] Plant height, biomass, leaf size and stem girth has been shown to decrease in maize under water limiting conditions.
[72] Crop plants exposed to drought stress suffer from reductions in leaf water potential and transpiration rate.
[72] The most negative impacts of drought for humans include crop failure, food crisis, famine, malnutrition, and poverty, which lead to loss of life and mass migration of people.
Further examples of social and health consequences include: Wind erosion is much more severe in arid areas and during times of drought.
[80] Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (Aeolian) sediment.
[81] It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick.
[84][85] Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a "tipping point" where it would irreversibly start to die.
According to the WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.
A 2005 study by Australian and American researchers investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago.
[87] In June 2008 it became known that an expert panel had warned of long term, maybe irreversible, severe ecological damage for the whole Murray-Darling basin if it did not receive sufficient water by October 2008.
[13] Australian environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth in Western Australia could become the world's first ghost metropolis, an abandoned city with no more water to sustain its population.
In the northern parts of the region within the Nile basin (Ethiopia, Sudan), the rainfall is characterized by an unimodal cycle with a wet season from July to September.
The frequent occurrence of hydrological extremes, like droughts and floods, harms the already vulnerable population suffering from severe poverty and economic turmoil.
Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by ever-increasing population densities.
Drought 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.
[100] Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon,[101] as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.
[102] Droughts can be scientifically explained in terms of physical mechanisms, which underlie natural disasters and are influenced by human impact on the environment.
