Short answers, pulled from the story.
The United Nations Convention to Combat Desertification defined desertification as land degradation in arid, semi-arid and dry sub-humid regions. This definition emerged from decades of scientific debate regarding the exact nature of soil loss.
Human activities such as tillage and overgrazing accelerate changes that natural processes create over geological time scales spanning thousands of years. The immediate cause remains the loss of vegetation cover which exposes soil to wind and water erosion.
The Sahel region of Africa has lost approximately six hundred fifty thousand square kilometers of productive agricultural land over the past five decades. Lake Chad located within this area has shrunk by over ninety percent since 1987 displacing millions of inhabitants.
The Great Green Wall initiative started in 2007 involves planting vegetation along a seven thousand seven hundred seventy-five kilometer stretch across fifteen countries. Senegal contributed to the project by planting fifty thousand acres of trees which improved land quality and economic opportunity.
Research conducted between 1982 and 2015 found six percent of global drylands underwent desertification driven by unsustainable practices compounded by climate change. Climate change is expected to increase dryland extent from thirty-eight percent in the late twentieth century to fifty or fifty-six percent by century end.