An unusual rainfall event is about to occur in the Sahara Desert, also known as the driest place on Earth. While the amount of rainfall may not be much by normal standards, much of the Sahara is expected to receive well over 500% of normal monthly rainfall in August and September.
This type of rainfall event doesn't happen often in the Sahara Desert – it's very rare, occurring on average less than once every 10 years – but it's usually a sign of some kind of change in the Earth's weather system and indicates unusual conditions in the atmosphere.
The driest place on earth
The Sahara Desert is said to be the driest place on Earth because it receives very little annual rainfall. It is the largest and hottest desert in the world, stretching from the Atlantic Ocean in the west to the Red Sea in the east. It covers an area of over 9.2 million square kilometers (3.6 million square miles).
The region is hot and dry because it is under a constant high pressure system known as the subtropical high, which causes air to descend, keeping the atmosphere dry and stable and preventing cloud formation and precipitation.
But the Sahara Desert wasn't always a hot wasteland. Just a few thousand years ago (6,000-11,000 years ago), it was a lush region with lakes, rivers, and rich vegetation. But changes in the Earth's orbit altered global weather patterns. As a result, that lush region suddenly turned into the driest land on Earth.
The images below compare what scientists think North Africa was like thousands of years ago: a lush region full of life, until climate change transformed it into the dry, hot region we know today.
Weather and precipitation
The image below shows the average monthly precipitation for August over the past 53 years. Notice how there is very little precipitation in the Sahara Desert region and only a small amount in the southern regions, but how much precipitation there is across the equator.
This tropical rainband is called the Intertropical Convergence Zone (ITCZ). It's basically a band of clouds, showers, storms, and rain that stretches across the equator. This feature occurs because trade winds from both hemispheres meet, creating updrafts, clouds, and rain.
You can see an example of the ITCZ in the image below: Tropical winds from both hemispheres meet near the equator, creating upward motion in the atmosphere, producing clouds, storms, and precipitation.
The ITCZ is very important because it influences the weather and climate of tropical countries. It also influences global weather systems and can affect the formation of tropical storms. Rainfall phenomena in the Sahara Desert also depend on the changes and movements of the ITCZ.
In the image below you can see the latest ITCZ analysis from NOAA. The black line shows the normal (expected) location of the ITCZ at this time of year. However, the red line shows the actual location of this anomaly, which you can see has shifted quite a bit further north.
The graph data gives further insight into the location of the ITCZ over Africa, showing that since June, the ITCZ has moved much further north than usual, which could dramatically change weather patterns in the region and potentially impact the Atlantic hurricane season.
As the entire ITCZ has shifted northward, the intense thunderstorm systems will move into the Atlantic Ocean through cooler waters at higher latitudes, meaning fewer tropical systems may intensify as they leave Africa in less favorable locations for them to organize and intensify.
This is just one of the indirect effects that the location of the African ITCZ has on North American weather, particularly the U.S. hurricane season.
But a more immediate effect of this northward movement is that it will bring unusual rainfall events deep into the Sahara.
Does it rain in the desert?
More than half of the Sahara receives less than 25 mm (1 inch) of rainfall per year. Occasionally, more rain falls in the south, where the ITCZ moves up and down. But most of the desert does not experience heavy rainfall every year, or even once a decade.
Below is the latest GFS model forecast for rainfall totals for the next 16 days. As you can see, the rainfall will cover much of the Sahara Desert. While it doesn't seem like a lot of rain, when you consider the annual rainfall totals, many areas will have several years' worth of rainfall in just a few days. Image by weathermodels.com using commercial license.
Below is a video animation showing the precipitation accumulations for the next 16 days. It gives a good idea of the progression and spread of rain across much of the Sahara Desert.
The anomalies paint a very clear picture. Anomalies are deviations from normal. The combined rainfall anomaly forecast below shows widespread rainfall anomalies over much of the Sahara Desert over the next two weeks and likely beyond.
If we look at the ECMWF ensemble precipitation totals, we can see that the actual precipitation totals are not that great – again, we can see that many areas are forecast to get several years' worth of rain in a two-week period.
ECMWF's long-term precipitation anomalies for early September also indicate significant rainfall anomalies occurring over much of the Sahara Desert, with rainfall forecast to continue over much of the desert into next month.
Looking more closely at September, the image below shows the % of normal precipitation forecast: As you can see, precipitation is reaching up to 500% around the fringes of the Sahara Desert, which means we can expect over 1000% of normal precipitation in the central areas over the coming days and weeks.
But how rare are these events really?
Unusual weather phenomenon
We decided to create a graph of precipitation in the Sahara Desert for the month of August. We can see the precipitation anomalies for each August over the last 53 years. There are only four years where the anomalies were large and wetter than the last 50 years, which means that this has happened four times in the last 50 years, which is less than once per decade.
Since the precipitation forecast also shows some significant anomalies in September, we decided to look at the September data for the same period and region. As we can see, there was only one strong precipitation event, in 1994. Data for 2024 is not yet available to give us the full picture, but based on the forecasts, it will be at least the second wettest year in recent decades.
A closer look at the 1994 precipitation anomalies shows that the overall anomalies were not as widespread as they appear in the current September forecast, which may suggest that this event could be a very significant year in history, if not the wettest year.
The potential for fall and winter across the US and Europe has yet to be fully investigated, but one thing is for sure: such strong and unusual weather anomalies could indicate major instability in the global weather system.
We will keep you updated on the upcoming weather trends for the season, so make sure to bookmark this page and if you saw this article on your Google app (Discover) feed, click the Like button (♥) to see more forecasts and the latest articles on weather and nature in general.
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