Snowing in a hot desert may seem like a paradox, but there have been several snowfalls recorded in the Sahara Desert over the last ten years, the most recent in January 2022. While this snowfall may seem unusual, it is not unprecedented.
Two distinct weather characteristics are required for snow to form: cold and moist air. The presence of snow reflects a special combination of air circulation in the atmosphere and the nature of the land surface on which snow falls.
While the Sahara usually experiences very high temperatures (more than 50°C), there are also very low temperatures, especially at night, due to the bare land surface and cloudless skies. For example, in January 2005, a cold of -14°C was recorded in Algeria during the northern hemisphere winter season.
Sahara is the largest hot desert in the world. It covers 11 countries in North Africa: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia. It is surrounded by the Atlantic Ocean in the west, the Red Sea in the east, the Mediterranean Sea in the north and the Sahel steppe in the south.
Winter air circulation patterns pull cool, moist air from the Atlantic and Mediterranean towards northern Sahara. This results in higher winter precipitation along the Sahara fringes this season.
At higher ground, such as the Atlas Mountains in Morocco and Algeria, rising air can cool, condense, and if the air is cold enough, moisture can freeze to form snow crystals and then a blanket of snow. If the land surface is also cold, the snow may be permanent and not melt immediately. Under these weather conditions and in these mountainous areas, snow can sometimes be seen in the Sahara.
The central Sahara is extremely arid and receives less than 100mm of precipitation per year, but it also has bodies of water on all four sides. From the Atlantic Ocean, the Mediterranean and the Indian Ocean, low pressure cyclones come to the region in the northern Sahara in winter, and wet air with monsoon rains in the southern Sahara in summer. Therefore, the periphery of the desert is wetter than its centre. This means that snow is more likely to form around the desert.
The Atlas Mountains especially serve as a snow trap due to their proximity to the Atlantic and their elevation. The Algerian town of Aïn Séfra saw snow in the northern hemisphere winters of 1979, 2016, 2017, 2018, 2021 and 2022. This latest event was a light dusting that covered the dunes with a thin white blanket, whereas in 2018, for example, up to 30cm of snow fell on the higher reaches. Although the Atlas Mountains contain mostly machine-made snow, there are several ski resorts, and evidence shows that it snows relatively frequently.
We do not yet have a definite answer as to whether the snowfall has increased in the Sahara. The reason we don’t have a definitive answer is partly due to a lack of data on past events and partly because climate modeling efforts have not focused on the low-population Sahara.
An important feature of the Sahara is its size (9 million km2) and its distance. This means that satellite remote sensing methods, rather than field observations, are now used to map the timing, amount and distribution of precipitation and snowfall. But that’s only in the last few decades: very little data on snowfall patterns is available before satellite recordings became available in the 1970s. So Saharan snowfall may be more common than we historically thought.
But globally, climate change also leads to unpredictable weather patterns. These changes could mean increased precipitation variability in the Sahara, along the wetter Sahel coast, and along the Atlantic and Mediterranean coasts.
If colder conditions in the mountains continue, snow events are likely to continue and are likely to become more volatile in terms of timing and quantity.
While snowfall patterns are uncertain, this is not the main challenge the Sahara faces under climate change. It is predicted that the land side of the mountains will be drier, and the center of the Sahara will remain dry and even warmer. Increasing dryness and unsustainable pumping and contamination of groundwater aquifers means less water is available for agriculture and growing cities.
In recent years, the Sahara itself has been growing as the southern Sahel has become drier and turned into a desert, and this situation is likely to continue in the coming years.
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