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NASA study finds a connection between wildfires, drought

ScienceDaily (January 10, 2017)

Titre : NASA study finds a connection between wildfires, drought

ScienceDaily (January 10, 2017)

For centuries drought has come and gone across northern sub-Saharan Africa. In recent years, water shortages have been most severe in the Sahel — a band of semi-arid land situated just south of the Sahara Desert and stretching coast-to-coast across the continent, from Senegal and Mauritania in the west to Sudan and Eritrea in the east. Drought struck the Sahel most recently in 2012, triggering food shortages for millions of people due to crop failure and soaring food prices.

Various factors influence these African droughts, both natural and human-caused. A periodic temperature shift in the Atlantic Ocean, known as the Atlantic Multi-decadal Oscillation, plays a role, as does overgrazing, which reduces vegetative cover, and therefore the ability of the soil to retain moisture. By replacing vegetative cover’s moist soil, which contributes water vapor to the atmosphere to help generate rainfall, with bare, shiny desert soil that merely reflects sunlight directly back into space, the capacity for rainfall is diminished.
Another human-caused culprit is biomass burning, as herders burn land to stimulate grass growth, and farmers burn the landscape to convert terrain into farming land and to get rid of unwanted biomass after the harvest season. As with overgrazing, fires dry out the soil and stymie the convection that brings rainfall. Small particles called aerosols that are released into the air by smoke may also reduce the likelihood of rainfall. This can happen because water vapor in the atmosphere condenses on certain types and sizes of aerosols called cloud condensation nuclei to form clouds ; when enough water vapor accumulates, rain droplets are formed. But have too many aerosols and the water vapor is spread out more diffusely to the point where rain droplets don’t materialize.

Story Source  : NASA/Goddard Space Flight Center.

Annonce (ScienceDaily)

Page publiée le 20 janvier 2018