Lake Assal: nothing cool, but still cool (1/3)

Intro: the warmest capital city

Together with Khartoum in Sudan, Djibouti city is the hottest capital in the world, having a yearly average temperature just a little shy of 30 degrees Celsius. While the “winters” are warm (kind of an european summer), the hot season is sweltering and the high humidity, characteristic for the coastal areas make the tropical ambience even more oppressive. The heat doesn’t go away even in the night, thus the living is very challenging without air conditioning, especially for non-natives. In the dark it almost feels unreal, like you are trapped inside a giant sauna without walls.

The city has a population of around 600.000, represented mostly by issa (somali) and afar ethnic groups with some arabs, french and other minorities beside. The former french colony is a busy strategic port close to the Red Sea’s Bab-el-Mandeb strait and more countries have military bases here. Before known as “French Somaliland”, after gaining the independence in 1977 the small country received the same name as its capital. Unknown for many travelers, the tourism is not very well developed here, but is rising in the recent years. Security is taken seriously, police presence is common. Djibouti’s downtown is quite noisy, with many honking green/ white taxis and old minibuses looking for the next passenger. Ambouli International Airport is close to the city and greeted me before midnight on June 18th with the first dose of african heat.

Mosque in the center area of Djibouti Ville

Choosing the target

The most iconic place associated with heat in the meteorological sense is undoubtedly the Sahara desert. An endless, empty place with the size of a continent presenting huge, sunbaked sand dunes and barren, rocky terrain. Temperatures are known to be very high there, often exceeding 50 degrees in the shade. Wait. Is this really true? Well, partially. Actually there were only a few cases when reliable temperatures above 50 degrees were measured here, the 51.3 degrees Celsius recorded in Ouargla (Algeria) on 6 July 2018 being the most certain one. Some old readings like the famous 58 degrees from El Aziziya were infirmed in the later years after specialistic investigation of the used equipment and measuring conditions. Long story short: naturally occuring +50 C air temperature is less common than people think.

Regarding my personal research, from the three main extreme categories (Cold, Heat, Amplitude) heat was the last to come. Actually it’s not exactly the first time, a few years ago I’ve visited the Ethiopian side of the Danakil depression with the same purpose, but the research was unsuccesful as I couldn’t collect the equipment from an inactive volcanic crater because of … let’s say “bad luck”, having to deal with unreliable local collaborators. Thus it’s understandable that I felt a strong need to come back to the Danakil and “finish the job”.

The sunken desertic area of tectonic origin is situated on the territory of three countries: Ethiopia, Eritrea and Djibouti. While the first one has the biggest portion, Djibouti owns the lowest spot, represented by the shores of Lac Assal at 155 meters below the sea level, also the deepest land in Africa and second in the world after the Dead Sea’s depression*.

The relief of Djibouti with Lake Assal in its center (teal color represents below sea level areas)

While second to the Dead Sea regarding the elevation, the raport between the two is reversed when we are talking about the salt concentration, Lake Assal being the saltiest lake of considerable size in the world (ten times more than the ocean), surpassed only by two small ponds (one in Antarctica, the other also in the Danakil), so one can easily float on the surface without sinking.

I have an old passion for below sea level places, which usually have a very hot climate (Death Valley in the USA is the best example). Why? There are two main reasons for this: first because of the general rule that normally temperature drops with elevation (6.4 degrees by 1 km), secondly because these places are parts of very dry, desertic environments, strong evaporation being a basic condition for their formation. A consequence of the latter is that they are often associated with salt marshes, the residue of the former lake. Badwater in Death Valley (-86 m), the southern part of the Dead Sea (around -400 m), Aydingkol in the Turpan Basin (-154 m) and Lake Assal (-155 m) all have these same two things in common: salt flats and extreme summer heat.

Soviet 500K topographical map of the Gulf of Tadjoura with Lac Assal on the left-center part

Dallol in the Ethiopian Danakil is considered to be the place with the highest average temperature in the world with a whopping 34.6 degrees Celsius, according to the short period of measurements from 1960 to 1966. June is the hottest month with a mean maximum of above 46 degrees, very similar to the well known “heavyweights” of the domain like Death Valley, the Kuwait-Iraq-Iran border area near the Persian Gulf (July-August) or the Jacobabad-Sibi plain in Pakistan (May-June). However, unlike the former mentioned ones which all reached 52-54 degrees at a certain time, no temperatures above 50 were ever recorded in Dallol, 48.9 C being the highest measurement. An unusually small gap of less then 3 degrees between the typical and the extreme values for sure, even for only 6-7 years of data. The heat is “at home” here, it’s never coming from somewhere else as in the case of most places (like Saharan origin heat in Europe for example), this must be the main reason for this constancy.

While before I’ve chosen the more interior part of the Danakil (Afdera Lake area) to completely avoid the moderating effect of the sea, now I knew that Djibouti’s Lac Assal is definitely not “too close” to the coast as in the summer months the wind (known as Khamsin) is blowing from the land, heating and drying everything on its way. The difference between the two regions is in the cooler part of the year when the wind is coming from the east (Indian Ocean), internal areas remaining warmer than coastal ones. Lake Assal’s southern shore is situated only 10 km away from the Ghoubbet-el-Kharab bay, an almost completely closed part at the very end of the Gulf of Aden. Actually the highly saline lake gets its water from this bay through the tectonic fissures.

The salt flats west of Lake Assal with the red dot marking the location of the data logger in the gorge

The general area was defined, let’s look at the small scale features. Basically I want to set the equipment at a little distance from the lake (respectively the salt pan) to have such ground below, which can heat up more (sand or gravel). Beside this I try to identify some topographical enhancement, without loosing too much elevation. After looking thoroughly everything around on GoogleEarth I found the right spot inside a gorge, just a few hundreds of meters from the salt flats. The dried riverbed’s name (known as “wadi” or “oued” in the arab world) is Kadda Galeita. Regarding the elevation the satellite data is not so precise here because of the small sizes, thus I partially concluded from the visual aspects that this place must be the best one for my purpose. Beside the general “canyon effect” (part of the solar radiation is reflected back by the walls), the concave curvature of the gorge is looking exactly to the NW, from where the strong sun will strike the slope in the early afternoon hours. Despite being on the Northern Hemisphere, because it’s inside the tropics, in this period of the year the sun passes slightly to the north above the land and June 21st is when the northern deflexion is the biggest.

In Djibouti the meteorological measurements are scarce. It seams that outside the capital’s airport there are no other weather stations at all, anything else is based on hypothetical approximations (both the regional forecasts and the climate diagrams). The city’s highest recorded temperature is 46 degrees Celsius (June and July), also just a few degrees above the summer months average maximums (40-42 degrees), a characteristic of the lower latitudes.

At present industrial scale salt extraction is happening at Lake Assal, consequently in the recent years can be reached on paved road. However the area is still kind of remote as there is no public transport from the Tadjoura main road, usually only expensive private tours and taxis are taking the tourists there. My target is about 10 km far from the “parking lot” (the end of the asphalt road).

*The Sea of Galilee (-212 m) often mentioned as the second lowest basin in the world actually is a part of the bigger Dead Sea depression. They are linked by the Jordan river, so can’t be considered a separate basin. However it is the second lowest lake.

Brief summary of the research

I arrived in Djibouti on June 18th in the late evening and after two days of rest and some acclimatization in the muggy heat of the capital, in the early morning of June 21st I was heading with a private driver to Lake Assal, which lies about 110 km west from the city.

After leaving the main Ethiopian road with heavy truck traffic, we continued on the Tadjoura way around the gulf of Ghoubbet, then turned left and reached the end of the asphalt road on the lake’s southern shore after 8 AM. From here I started the hike on the salt pan towards the target situated inside the gorge.

Haze on the salt flats of Lake Assal

The weather was already hot and became oppressive while reaching the exact location in the wadi after 10 AM. There were only a few clouds, but the characteristic summer haze caused by the hot and dry khamsin wind was present. However, I felt only weak air movement until now.

The bubble-aluminium foil protected data logger (I positioned the device’s screen to face south) and the Barani solar radiation shield under which its sensor was sheltered were mounted on a tripod whose legs were farther stabilized with nearby rocks.

The weather station in the gorge

The exact coordinates are: 11.686346 N, 42.341225 E, the elevation around -130 meters. The height of the sensor from the ground is 160-170 cm. At 10:43 AM the mini weather station started its operation. First reading: 42.4 degrees Celsius.

I waited in the shade nearby the research equipment until late afternoon, meanwhile checking the temperature more times and measuring also the ground in the early afternoon. With some luck I caught the highest air temperature live: 47.4 degrees Celsius around 4 PM and saw 73.9 C on sandy surface around 1 PM. The sky was partially covered in the hottest period, but the clouds coming from the NW never managed to block the sun.

The highest temperature of the day and of the entire measuring interval

After a sandstorm, which hit my camp in the early evening, I’ve spent the following night outside, hiking back to the asphalt road until the morning were my driver picked me up. The evening and night was still extremely hot, this phenomenon felt even more outlandish than the peak heat of the day.

I couldn’t sleep or even rest until dawn as the temperature never dropped below the human body’s and the hot wind was making the real feel even worse. Meanwile the sky became cloudier. This night’s minimum temperature in the gorge was 39.4 C !

My diurnal shelter, an overhang of the rock wall

I’ve spent the next days sleeping in the city with two separate trips to the Ghoubbet-el-Kharab bay using public transport: one to the volcanic area with new lava fields on the western side of the gulf and one to the higher plateau on the south-eastern part. Because of the proximity to the ocean, the capital is much more humid than the internal areas, having the heat index higher for the same temperatures. Here you are constantly sweaty, while at Lake Assal the khamsin sucks out all moisture from you.

I returned to collect the equipment on 26th in the late afternoon (haze again) and found the tripod standing in its place on the wadi’s floor with the logger functional and everything intact. The research was successful, all data was correctly recorded. The first day’s 47.4 degrees wasn’t surpassed on any other day, but was approached on 23rd with 47.2 degrees. The lowest daily maximum was 44.3 on 22nd, while the minimum of the entire measuring period 33.3 degrees Celsius in the morning of 25th.

Dromedaries grazing in the desolate landscape

During my staying in the Lake Assal area I didn’t encountered any wild animals outside of four camels and hearing some high pitched bird noises inside the gorge. The vegetation is completely missing on the salt flats and is also very scarce on the sandy-gravel surface. No acacia trees, only some small tufts. At the end of the asphalt road live some locals (mostly youngsters) who sell salt and other mineral related souvenirs and there is some activity at a chinese salt extraction plant. No other tourists were present as it is low season because of the heat.

The instruments used on the field

-One LogTag UTRED30-16 data logger with the measuring range between -40 and +99 degrees Celsius, an accuracy of 0.5 degrees Celsius and a resolution of 0.1 degrees Celsius.

-One Greisinger GMH 2710-T digital precision thermometer with the measuring range between -199.9, +200 degrees Celsius, an accuracy of +-0.1 degrees Celsius and a resolution of 0.1 degrees Celsius.

-One photo camera tripod serving as the support for the instruments.

-One helical solar radiation shield from Barani Design Technologies:

Sand surface measurement with the Greisinger precision thermometer

To be continued…

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