Planet Earth is a living planet, so much so that when temperatures rise in one place, they fall in another to maintain global thermal equilibrium. Something similar is going to happen with the Mediterranean and the Sahel: in the last 20 years, the Mediterranean region has experienced an increase in temperatures and a decrease in rainfall, which appears to have shifted to the Sahel , as revealed in a study published in the journal Nature Climate Change, conducted by the Max Planck Institute for Meteorology.
Due to the increase in temperatures in the Mare Nostrum, the humidity that reaches the southern limit of the Sahara at the beginning of the West African monsoon in June is also higher, so the Sahel becomes greener.
The Sahel's climate is highly variable, dominated by the West African monsoon, which brings rain from June to September. The rest of the year is marked by intense drought. The land heats up more than the ocean in summer because the sun is higher in the sky, and oceans do not absorb heat as quickly as land. Air rises from the continent, drawing moisture from the sea into the Sahel.
The intensity of the monsoon has varied over time. Between 1950 and 1960, the Sahel experienced a wet period; in the 1980s, the drought was so severe that more than 100.000 people lost their lives. Since then, rainfall has returned.
The cause, according to scientists, is the warming of the Mediterranean . To reach this conclusion, they studied different scenarios using various simulations. They were able to determine that if the temperature in the Mediterranean region remains more or less constant, rainfall in the Sahel does not increase; conversely, if the Mediterranean warms, it rains more in the Sahel.
This is because not only the temperature rises, but also the humidity, which is what "activates" the West African monsoon. In this way, in this part of Africa, they can enjoy more rains at the beginning of the rainy season.
You can read the study here (in English).