Drought struck the Sahel most recently in 2012, triggering food shortages for millions of people due to crop failure and soaring food prices. 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. 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. To do so, Ichoku and his colleagues used satellite records from 2001 to 2014 -- including data from NASA's Moderate Resolution Imaging Spectroradiometer and the Tropical Rainfall Measurement Mission -- to analyze the impact of fires on various water cycle indicators, namely soil moisture, precipitation, evapotranspiration and vegetation greenness. The results so far show only a correlation between fires and water cycle indicators, but the data gathered from the study is allowing scientists to improve climate models to be able to establish a more direct relationship between biomass burning and its impacts on drought.
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May 2017
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