[Someone]

https://catalogue.unccd.int/1551_GGW_Report_ENG_Final_040920... says they pivoted a bit:

“The aim of the GGW was originally to create a long vegetation barrier between the 100 and 400 mm isohyets, including ramps, and over a length of at least 7000 km along the Sahel, being roughly 15 km wide. In recent years this vision has evolved into an integrated ecosystem management approach, striving for a mosaic of different land use and production systems, including sustainable dryland management and restoration, the regeneration of natural vegetation as well as water retention and conservation measures”

I think that makes it hard to report % completed. Also, 4% is a lot of land (that same PDF says they currently target about 1½ million km² of land. That’s a lot more than that 7,000 by 15 km band originally envisioned (For comparison, the USA and Canada each are about 10 million km², so that would be about 7½% of North America), in the poorest part of the world.

As https://www.pri.org/stories/2016-05-02/africas-great-green-w... says “it will take at least a generation to make it a reality”