A simple introduction to this answer can revolve around a general statement about Sahara Desert.

The Sahara desert covers an area of around 9,200,000 square kilometres and is one of the largest hot deserts in the world.

Deserts are defined by low average annual rainfall — usually 100 millimeters (less than 4 inches) of rain per year or less.

The cyclic transformation of the Sahara Desert into savannah and woodland ecosystems is one of the most remarkable environmental changes on the planet.

According to the research study that was published in the journal Nature Communications, the periodic wet phases in the Sahara desert were caused by changes in Earth’s orbit around the Sun

Body

You may incorporate some of the following points in the body of your answer:

Possible Reasons

Increase in the African Humid period which could have allowed the dispersal of various species.

There is already a lot of evidence to back up the hypothesis that the Sahara was once vegetation. These “North African humid periods” may have had a significant influence in the establishment of vegetation passageways out of Africa.

The greenings of the Sahara Desert could have been driven by changes in Earth’s orbital precession.

The Earth’s spin influences seasonality over an approximately 21,000-year cycle. The changes in precession also decide the amount of energy received by the planet during different seasons.

These changes caused warmer summers in the Northern hemisphere and thereby increased the strength of the West African monsoon system which has increased rain in the Sahara, causing the spread of savannah-type vegetation through the desert.

Conclusion

You can add a simple conclusion like the following

Sahara's transformation is a topic of ongoing research, and our understanding of the mechanisms involved continues to evolve. Additionally, human-induced climate change may be influencing the Sahara's climate in ways that are not fully understood. Studying past climate records, modeling future scenarios, and monitoring current conditions are essential for gaining a more comprehensive understanding of the complex processes involved in the transformation of the Sahara Desert into savannah and woodland ecosystems.

Other Points to Consider

Species living in the Sahara Desert

Countries covered under the Sahara Desert

Rivers flowing through the Sahara Desert