Zai in Sahel region. Successful story of re-greening the Sahara

According to an FAO classification based on average annual precipitation and agricultural features there are four different eco-climatic zones in the Sahel region:

Sahel Region

Sahelian zone: Where average annual precipitation ranges between 250 and 500 mm. This zone is at the limit of perennial vegetation. In parts where precipitation is less than 350 mm, only pastures and occasional short-cycle drought-resistant cereal crops are grown; all cropping in this zone is subject to high risk.

Sudano-Sahelian zone: Where average annual precipitation ranges from 500 to 900 mm. In those parts of this zone where precipitation is less than 700 mm, mostly crops with a short growing cycle of 90 days are generally cultivated predominantly sorghum and millet.

Sudanian zone: Where average annual precipitation ranges from 900 to 1 100 mm. In this zone, most cereal crops have a growing cycle of 120 days or more. Most cereals, notably maize, root and cash crops are grown in this zone.

Guinean zone: Where average annual precipitation exceeds 1 100 mm. Guinea-Bissau and a small area of southern Burkina Faso belong to this zone, more suited to root crop cultivation.

The zai method helps farmers cultivating crops in a region characterized by arid soils and limited rainfalls.
However, only the introduction of adequate policies and important investments in infrastructures could leverage the success of local initiatives in the implementation of effective food security strategies  at national scale. A number of important issues to be considered for future action were pointed out in the paper entitled Regreening the Sahel published by the International Fund for Agricultural Development (IFAD):

Lessons learned*

Policy changes are essential for the success of on-farm regreening in the Sahel, and the

process should continue. National policies and legislation must support farmer investment

in trees, and farmers should be granted exclusive rights to the trees in their fields.

A wide range of other factors can contribute to this process:

• substantial public support for private investment in soil and water conservation;

• improvement of trunk roads, which reduces transport costs and allows traders to send

their trucks to remote areas to buy new products;

• generally sound macroeconomic management, without discrimination against

agriculture and natural resources;

• substantial local capacity-building by NGOs and other stakeholders (technical,

organizational and management skills);

• government action to increase awareness of environmental problems and their

solutions

Further info also in the following blog:
Global Warming & Terra Forming Terra: Agroforestry Revolution in Sahel