Please define desertification and explain where it takes place. Desertification is when unsustainable land use practices and environmental change lead to land degradation that leaves agricultural land no longer usable. It is taking place all over the world. Desertification is when climate change makes an area hotter and dryer Desertification is when sand dunes take over agricultural land or human habitation. It happens primarily in the Sahel Desertification is when sand dunes take over agricultural land or human habitation. It happens primarily in the Sahel, and around the Kalahari, the Namib and the Guban deserts