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The Atacama is always said to be the driest place on Earth, while it's actually not true because the Sahara is even drier for three reasons :
1 ~ The Sahara constitutes a much larger area with similarly low annual mean rainfall totals as those of the Atacama, and many places (e.g Aswan, Luxor, Kufra, Wadi Halfa, Kharga, Tazerbo...) are virtually rainless, recording on average about 0.5 mm of precipitation yearly.
2 ~ The so-called "dryness ratio" is much higher in the Sahara than in the Atacama because the rates of evaporation are way greater in the former : Egypt and Libya must be the driest places on Earth with a dryness ratio of 200+ while the Atacama has a mere 10-50+.
3 ~ There is an annual cycle of high air moisture in the Atacama in contrast to much of the Sahara, where extreme aridity relentlessly prevails. Rainfall is actually even less likely in the great African desert, in terms of intensity and frequency, too.
The Atacama is always said to be the driest place on Earth, while it's actually not true because the Sahara is even drier for three reasons :
1 ~ The Sahara constitutes a much larger area with similarly low annual mean rainfall totals as those of the Atacama, and many places (e.g Aswan, Luxor, Kufra, Wadi Halfa, Kharga, Tazerbo...) are virtually rainless, recording on average about 0.5 mm of precipitation yearly.
2 ~ The so-called "dryness ratio" is much higher in the Sahara than in the Atacama because the rates of evaporation are way greater in the former : Egypt and Libya must be the driest places on Earth with a dryness ratio of 200+ while the Atacama has a mere 10-50+.
3 ~ There is an annual cycle of high air moisture in the Atacama in contrast to much of the Sahara, where extreme aridity relentlessly prevails. Rainfall is actually even less likely in the great African desert, in terms of intensity and frequency, too.
Arica once went 14 years without rain. Can anywhere in the Sahara match or beat that?
Yes! Kufra, in the southeastern corner of Libya, once went 12 consecutive years without any rain at all and Aswan is so dry that people who live over there don't even remember the last time it rained!
At In Salah, in the heart of the Algerian Desert, a period of 7 successive absolutely rainless years was once recorded!
Last edited by Special_Finder; 12-19-2015 at 12:45 PM..
Nowhere in the Sahara has a record to match Quillagua in the Atacama. In a 50-year span only 4mm fell in 3 rain events. A freak addition of 4mm this year (when Antofagasta had 14 years' worth in a single day) still leaves it with an average of less than 0.2mm/year. A 30-year average of 1.4mm is cited for Aswan, allegedly from WMO sources, and that is higher than the 0.8mm for Arica.
In terms of average annual rainfall on an areal basis, the Atacama would be drier than the Sahara - the western Sahara is considerably "wetter" than the eastern parts. There are various parts of the Atacama where it is alleged that rain has never been recorded in modern times.
Nowhere in the Sahara has a record to match Quillagua in the Atacama. In a 50-year span only 4mm fell in 3 rain events. A freak addition of 4mm this year (when Antofagasta had 14 years' worth in a single day) still leaves it with an average of less than 0.2mm/year. A 30-year average of 1.4mm is cited for Aswan, allegedly from WMO sources, and that is higher than the 0.8mm for Arica.
In terms of average annual rainfall on an areal basis, the Atacama would be drier than the Sahara - the western Sahara is considerably "wetter" than the eastern parts. There are various parts of the Atacama where it is alleged that rain has never been recorded in modern times.
Edited for decimal point error.
The average annual rainfall amount over the whole of the Sahara, over an area of 8 millions km² or more, is only 20-25 mm. You're right on the fact that the eastern Sahara is drier than the western section, but the latter stay very dry all the same (e.g. In Salah, Algeria : 14,7 mm a year on average ; Taoudenni, Mali : about 5 mm annually). Many sources claim that Aswan gets no more than 0.3-0.7 mm, so it needs additional verification. There are other spots in the central/eastern Sahara which must be even drier than Aswan such as Wadi Halfa, Sudan and Talha, Chad.
In March 2014, Upper Egypt and the Nile Valley were flooded because 29 mm suddenly fell in Luxor when 15 mm fell in Aswan, the same day. This means that the equivalent of 30 years of rainfall fell on almost one or two days! Many children were affraid by that extreme weather event!
The Sahara has the advantage to be extremely vast, so I wouldn't be surprised to discover or to find an area and/or a thin spot where rainfall is lighter and even more unlikely than the Atacama, given the stability and the strength of the subtropical high pressure, and over there precipitation-generating mechanisms are really limited and inhibited.
Last edited by Special_Finder; 12-20-2015 at 01:07 AM..
To be pedantic, one needs to consider the Dry Valleys of Antarctica - albeit not a large area by comparison with the deserts.
I agree on that fact. The Dry Valleys of Antarctica are virtually rainless, too, but they are so cold.
Must we take in account the rate of evaporation in order to determine what are the driest places on Earth? Because, with the same annual average rainfall amount, a place will be drier than another if the evaporative power of the air is greater, as it makes precipitation less effective.
I agree on that fact. The Dry Valleys of Antarctica are virtually rainless, too, but they are so cold.
Must we take in account the rate of evaporation in order to determine what are the driest places on Earth? Because, with the same annual average rainfall amount, a place will be drier than another if the evaporative power of the air is greater, as it makes precipitation less effective.
The dry valleys are devoid of any precipitation insofar that none reaches the ground. A remarkable region.
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