If the predictions prove true, many desert regions will receive the equivalent of several years of rain in the coming days and set a historical record, an anomaly produced by the alteration of atmospheric flows.
Rising temperatures will exceed human limits and make large areas of the planet uninhabitable.
The forecast by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the first half of September in North Africa is of great interest to meteorologists. The model predicts a period of intense rain in the Sahara Desert, with precipitation reaching 50 litres per square metre in inland areas where there is virtually no rain. “Many regions will receive the equivalent of several years’ worth of rain in the space of two weeks,” says Andrej Flis, one of the first specialists to warn of the situation.
In the bordering desert areas, the model predicts that rainfall will increase by 500% above average this month, with some central regions receiving more than 1,000% of normal rainfall in the coming days and weeks. “What we are seeing is totally exceptional,” acknowledges José Luis Camacho, spokesman for the National Meteorological Agency (AEMET). “The prediction shows a system that does not die, that stays there, strengthening. “The water will fall through a pipe and it is predictable that there will be damage in an area where houses are made of mud.”
“Up to 30 litres are expected to fall on Friday and Saturday next week in eastern Morocco and western Algeria,” says Ricardo García Herrera, professor of atmospheric physics at the Complutense University of Madrid (UCM). “If that happens, it will be brutal. The trail of water that will be there will turn into dunes in some areas. However, the expert warns, there is a certain level of uncertainty, because even if the model is quite reliable, “we are talking about a ten-day forecast, at the limit of predictability.”
“We must bear in mind that these are eminently convective precipitations, not fronts, and this always implies a greater degree of uncertainty,” warns Francisco Martín León, meteorologist and coordinator of RAM (Meteorology Amateur Magazine). In 38 years of experience at AEMET, he explains, given these entries of humid air that cross the desert, the model overestimates these predictions for so many days. “That is why I cannot believe the model one hundred percent, but the possibility that we have a historic eruption is there,” he says. “There are maps that give a probability of between 20 and 30% – which is quite high – that in ten days these 50 liters per square meter will be exceeded in desert areas, and this has an intrinsic value.”
The tropics have moved north
The factors that led to this anomaly still require more detailed examination, but all indications are that the Intertropical Convergence Zone (ITCZ), a band of clouds, rain, storms and precipitation that stretches across the equator, is ha moved much further north than usual. In addition to causing this rare rainfall inside the Sahara Desert, this may explain a drastic change in weather conditions in the region and affect the Atlantic hurricane season, reducing their formation.
The atmospheric flow is disturbed and precipitation is spreading towards the Sahara. Everything is moving north, this is not normal
“We have to look at the surface temperature of the ocean,” Camacho explains. “We have the La Niña phenomenon in the tropical Pacific, which produces cooling, but it turns out that in the Atlantic there is also an extension of cold waters that are heading towards the Gulf of Guinea, colder than normal, like an Atlantic Niña.” In late August and early September, it is normal for it to rain in this area located south of the desert, recalls the AEMET spokesman. “There is a West African monsoon, which transports moisture from the Gulf of Guinea to the Sahel, but now the atmospheric flow is disturbed and the precipitation extends towards the Sahara. “Everything is moving north, it is not normal.”
Martín León observes that there is also a very particular circumstance, which is that the situation is the result of the conjunction of three elements: an irruption of polar air to the north-northwest of the Iberian Peninsula, a dana to the northwest of the Canary Islands and a depression zone around Mauritania. “These three elements cause a tongue of humidity that penetrates the desert and projects towards our latitudes, so that at the end of the episode these rains can reach the peninsula,” he says.
Attributable to climate change?
For seasoned meteorologist Ángel Rivera, an expert in atmospheric dynamics, the fact that there is a precipitation anomaly in the desert cannot be considered a consequence of climate change and could remain within the natural atmospheric variability of this time of year. “This is something that attribution experts will have to study,” he warns. “If climate change intervenes, researchers will see it,” acknowledges Camacho. “In this area there is a lot of multi-cadal variability,” says García Herrera, who has published a study on the West African monsoon with data collected by ships since 1800. “Our data show that in the second half of the 19th century, in the Sahel, the rains were intense and the area has been in drought since 1970,” he says.
Extreme weather events cannot be directly equated with climate change, but we are in a situation we have never experienced in modern times: very warm seas and an atmosphere boosted by excess heat and humidity.
For the specialist, there is no doubt that this is a somewhat strange year, since the conditions are ripe for it to be a year with quite a few hurricanes in the Atlantic and there has only been one yet. “The problem is that there is no historical data to compare the rainfall with, we do not know to what extent it is a coincidence or causality, although it is probably very rare,” admits García Herrera. “The origin is that the monsoon trough has reached a very high level, but considering it as an advance in climate change is unfounded,” he says. “We will have to see, but as almost always, it will be due to a combination of things.”
Recurring instability
Whatever happens, we must not forget that this anomaly occurs in a context in which tropical rains are expected to move increasingly northward, as a result of the climate crisis. “Of course, an extreme weather phenomenon cannot be directly equated with climate change; attribution studies will have to be carried out,” explains Martín León. “But we must bear in mind that we are in a situation that we have never been in in modern times, with very warm seas, with a wild Atlantic, with a Mediterranean with extremely high temperatures, with an atmosphere doped with more heat and more water vapour, and all this indicates that climate change could be the cause of all this.
“There is increasing evidence of changes in weather patterns and atmospheric dynamics that may be linked to the accelerated warming occurring on the planet,” says José Miguel Viñas, a meteorologist at Meteored.
There is growing evidence of changes in weather patterns and atmospheric dynamics that may be linked to accelerated warming.
If the forecast is correct, it will be at least the second wettest year in recent decades and the largest anomaly since 1994, which it could well exceed. There is now concern about the damage that the rainfall could cause in a region of the planet where houses are made of mud and are not prepared to receive water. “If years and years go by without hardly any rain and 50 liters per square meter fall in one day, the houses are damaged,” explains Camacho. “It is likely that in Niger this will cause the houses to collapse, because they are made of mud. And another aspect to take into account will be the subsequent locust invasions, which occur whenever large amounts of water fall in the region.”
“The current phenomenon could go down in history books, even among the wettest years,” concludes Andrej Flis. “One thing is certain: such strong and infrequent weather anomalies can indicate a great instability of the global weather system.”
