09/08/2024 – 17:09
A survey by the meteorological company MetSul released last Friday, the 6th, shows that a large part of Brazil currently has lower humidity levels than the Sahara, in northern Africa.
While the country is experiencing a prolonged drought, parts of the desert have been showing very high humidity levels for local standards, with the possibility of exceptionally rare rainfall for the period.
In September, almost all regions of Brazil have shown extremely low relative humidity levels, equal to or below 10%.
On Friday, the 6th, the National Institute of Meteorology (Inmet) maintained the orange alert for low humidity in the Federal District, São Paulo and 15 other states.
The federal agency also registers a yellow alert, of potential danger due to low humidity, in three states: Rio de Janeiro, Santa Catarina and Paraná.
There is currently an exceptionally dry air mass acting over Brazil. According to the MetSul statement, it is normal for the central region of the country to have low humidity at this time of year, but the situation has been aggravated by a number of factors: a prolonged drought in several parts of the country, with the dry season starting earlier, and a low frequency of cold fronts reaching the central part of Brazil.
The cycle feeds back into the lower soil moisture, due to the low volume of rainfall, and high temperatures.
The dry weather has contributed to the reduction of river levels, especially in the Amazon, and to warnings of fire risk in several regions of the country, including the interior of São Paulo.
According to the Burnings Program, from the National Institute for Space Research (INPE), Brazil registered 8,225 fire outbreaks in the last 48 hours in all biomes, with one or more active fire fronts.
How the comparison was made
MetSul’s analysis was based on surface observation data and numerical models. In the first approach, data were collected from airport stations in the capitals of countries located in the desert region of North Africa. The lowest humidity levels recorded in these locations on Thursday, the 5th, were: 36% in Cairo (Egypt), 52% in Niamey (Niger) and Algiers (Algeria), 59% in Bamako (Mali) and 84% in N’Djamena (Chad).
The strategy was used due to the limitations of monitoring in the desert, as it is a predominantly uninhabited region, and also due to conflicts in these countries, explains MetSul.
The company also compared the relative humidity in Brazil and the Sahara during the afternoon of Friday, 6, using computer models, confirming that the desert is more humid than the country.
Maps from the North American GFS model indicate that air humidity is high in many areas of the Center and towards the East. In the Sahel region, further south, humidity levels are very high by local standards. The driest area is the sector west of the Sahara.
Rains in the Sahara
Computer models have shown record amounts of rainfall in the Sahara, which averages just 3 inches (7.62 centimeters) of precipitation over the entire year.
In the first few weeks of September, some parts of the desert have received five times the average rainfall for August and September, with some areas set to see rainfall recorded for the first time in those months.
The rare event, which usually happens once in a decade, could bring pockets of flooding to parts of Chad, Libya, Niger and Algeria this year. Half of the Sahara receives less than an inch of rain annually.
Under normal conditions, a semi-stagnant high-pressure system brings sinking air into the Sahara, which heats and dries it. The sinking also crushes any pockets of rising air needed to generate clouds and thunderstorms. This is why the desert is normally so hot and dry.
But a band of low pressure – known as the Intertropical Convergence Zone – is bringing storms to areas where they don’t usually occur. Mali and Mauritania are among the regions receiving above-average rainfall due to the phenomenon, which is expected to turn to western and northern Algeria.
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