The United Nations' World Day to Combat Desertification and Drought is annually observed on June 17 to highlight the urgent need to curb the desertification process. It also aims to strengthen the visibility of the drylands issue on the international environmental agenda.
In December 1994, the United Nations General Assembly declared June 17 the World Day to Combat Desertification and Drought. The assembly acknowledged that desertification and drought were global problems because they affected all regions of the world.
The assembly also realized that joint action by the international community was needed to combat desertification and drought, particularly in Africa.
States were invited to devote the World Day to promoting awareness of the need for international cooperation to combat desertification and the effects of drought, and on the implementation of the Convention to Combat Desertification.
Since then, country parties to the United Nations Convention to Combat Desertification (UNCCD), non-governmental organizations and other interested stakeholders celebrate this particular day with outreach activities worldwide on June 17 each year.
According to en.wikipedia & timeanddate