Over a period of five days, the southern Algerian city of Tamanrasset has received 45mm of rain. That is a remarkable amount of rain simply because it is more than is expected in an entire year.

Tamanrasset sits in a wadi, or valley, of the Ahhagar massif, a large volcanic mountain range in the Sahara Desert. Much of this massif is a national park and contains the famous hermitage site of Assekrem.

Assekrem is high in the mountains, 2,700 metres above sea level, and has an annual rainfall of 118mm. Surprisingly, this is almost three times as much as Tamanrasset which sits at a lower 1,400 metres.

Assekrem, in the same five days between March 19 and 24, exceeded its annual rainfall expectation, with 130mm caught in the rain gauge. This represents 110 per cent of average annual rainfall, as calculated from a respectable 50-year archive.

Mountains are good producers of rain, as they force air to rise, cool and release its moisture. In the Sahara though, it is usually too dry to have enough moisture to release.

This March, enough water vapour made it from the Atlantic, across the western desert, to make the Algerian wadis green. Satellite pictures still show the long streak of cloud, stretching from Guinea to Libya, which gave the rain.

The rain has now stopped in the Ahhagar mountains, but there are still unusually early showers showing up in the sahel, in Niger and Mali.

Source: Al Jazeera