The causes of desertification are:
(i) Natural factors
(a) Drought: It affects productivity of land and growth of natural vegetation, thereby leading to desertification.
(b) Global warming: Increase in temperature due to global warming makes the desert environment more dry, accelerating desertification.
(ii) Human factors
(a) Human activities: It includes overgrazing, expansion of agriculture and deforestation.
(b) Population growth: Growth in population has increased pressure in the desert and semi-desert areas which creates expansion of deserts.