Rain in the Sahara Desert: A Sign of Change
Today, rain is falling in the Sahara Desert, one of the driest places on Earth. Moisture from the African monsoon has moved far north of its normal tropical extent into the center of the Sahara Desert. Rain is falling in places it hasn’t fallen in years.
Unusual Weather Patterns
The African monsoon moved north of its normal region in August, bringing some locations in North Africa many times their normal rain. American and European weather and climate models forecast that the monsoon rains will continue for the next two weeks or more as the African monsoon will continue to be displaced far north of its normal tropical position.
Expert Insights
At Severe Weather Europe, Andrej Flis explained how unusual this Saharan rain is. A unique rainfall event is currently unfolding across the Sahara Desert, one of the driest places on Earth. The amount of rainfall might not seem large by normal standards, but a large part of the Sahara will get well over 500% of normal monthly rainfall in September.
Rare Rainfall Events
It’s not very often that the Sahara Desert experiences these rainfall events. They are very rare, less than once per decade on average, but they are usually a sign that something is changing in the Earth’s weather system, indicating an unusual state of the atmosphere as we head into autumn and winter.
Normal Conditions vs. Current Conditions
In normal years, the subtropical high-pressure area, a heat dome, sits relentlessly over the Sahara. The sands are so reflective, the air so dry, and the ground is so hot that heat is actually lost to space over the Sahara under normal conditions. That leads to hot days and cool nights with huge temperature swings, especially near the equinoxes. This September’s equinox period will be very abnormal with cooler days, warmer nights, and intrusions of tropical air from the African monsoon.
A Historical Perspective
The Sahara wasn’t always a desert. From the beginning of the interglacial period up to 6000 years ago, there were lakes in the Sahara. Megalake Chad and other Saharan lakes were so large that they kept the climate moist even after the orbital parameters that brought maximum insolation to the Arctic in late spring and early summer ended the last glacial period became less favorable. However, 6000 years ago, the solar heating patterns caused by Earth’s orbital variations brought more ocean warming to the southern hemisphere and less to the northern hemisphere, and the North Atlantic cooled. The cooling of the North Atlantic waters brought on the drying of the Sahara and the desert conditions that have predominated the region for the past 5000 years.
Current Climate Changes
But this summer, something is different. The waters of the North Atlantic are relatively hot while the waters of the South Atlantic are relatively cool. And the waters of the Indian Ocean on the east coast of Africa are very warm. And the Mediterranean Sea is hot.
The high heat content of the North Atlantic and the Mediterranean Sea has affected the atmospheric circulation patterns, bringing exceptional heat to far northern Europe and allowing the heat dome over western North Africa to break down, bringing monsoon moisture north into the Sahara Desert.
Human Impact
The heating of the North Atlantic caused by human activities, in particular, greenhouse gas (GHG) emissions, may be creating conditions similar to those that brought the African monsoon into the Sahara 6000 years ago. Climate models have predicted that the Sahara could become wetter with increasing GHG emissions, and that appears to be beginning this year.
Good News and Bad News
There is good news in this. The atmospheric waves that move into the North Atlantic that develop into tropical storms have been displaced far north of their normal track this August and early September. They have moved into cooler waters. The waters of the main development region for Atlantic hurricanes are very hot, but without the strong tropical waves over the warm waters, the hurricane season has gone quiet.
The bad news is the humidification of the Sahara leads to increased global uptake of solar heat because water vapor is a strong greenhouse gas.
FAQs About Monsoon Rain in the Sahara Desert
1. What is causing the monsoon rain in the Sahara Desert?
The monsoon rain in the Sahara Desert is primarily caused by a rare alignment of atmospheric conditions, including a low-pressure system and moisture from the Atlantic Ocean.
2. How often does it rain in the Sahara Desert?
The Sahara Desert is one of the driest places on Earth, with most years receiving less than 1 inch (25 mm) of rainfall. The recent monsoon rain is an unusual event.
3. What are the effects of monsoon rain on the Sahara Desert ecosystem?
The monsoon rain brings much-needed water to the desert, revitalizing vegetation and replenishing water sources. This can have a positive impact on local wildlife and agriculture.
4. Are there any historical precedents for monsoon rain in the Sahara Desert?
While rare, there have been instances of heavy rainfall in the Sahara Desert throughout history. However, these events are typically isolated and do not occur frequently.
5. How does this event compare to previous instances of heavy rainfall in the Sahara?
This event is notable for its widespread and prolonged nature, affecting a larger area than previous instances of heavy rainfall in the region.
6. What are the implications for climate change?
The occurrence of monsoon rain in the Sahara Desert could be an indicator of changing global climate patterns. It highlights the potential for more extreme weather events due to climate change.
7. How is the local population affected by the monsoon rain?
The local population may experience both positive and negative impacts. While the rain can bring relief and new opportunities for agriculture, it also poses risks such as flash flooding and potential disruptions to daily life.
8. Are there any concerns about flash flooding or landslides?
Yes, there are concerns about flash flooding and landslides due to the sudden and heavy rainfall. Local authorities are advising residents to be cautious and prepared for potential hazards.
9. How is the international community responding to this event?
The international community is closely monitoring the situation, with some organizations providing aid and support to affected areas. However, the response is largely observational at this stage.
10. What can we expect in the coming weeks and months after the monsoon rain?
In the coming weeks and months, the region can expect a mix of dry and wet conditions. The impact of the monsoon rain will be closely watched as it may lead to longer-term changes in the desert’s ecosystem.