If you’re on a day trip to the Sahara Desert in North Africa, you’ll want to bring plenty of water and lots of sunscreen. But in fact, if you plan to stay overnight, you should also bring a suitable sleeping bag to keep warm.
This is because temperatures in the Sahara can drop drastically as the Sun goes down, from an average high of 38 degrees C in the daytime to an average low of minus 4 degrees Celsius at night.
The question is, why is this dramatic temperature change happening in arid deserts like the Sahara? How do indigenous plants and animals deal with such rapid temperature changes?
The reason the arid deserts, the arid regions that make up about 35% of the Earth’s area, become so hot and then too cold, is a combination of two key factors: sand and moisture.
According to a 2008 report from NASA’s Jet Propulsion Laboratory in Pasadena, California, when heat and light from the Sun hit the sand desert, grains of sand in the top layer of the desert absorb and release heat back to the air.
During the daytime, the solar radiation of the sand heats the air and causes the temperature to rise. However, at night, most of the heat in the sand radiates to the air quickly and there is no sunlight to heat it, causing the sand and its surroundings to become colder than before.
However, this phenomenon alone did not explain such a severe drop in temperature. The main cause of the severe temperature changes is that the air in the desert is very dry. In arid deserts like the Sahara and the Atacama Desert in Chile, humidity - the amount of water vapor in the air - is practically zero, and unlike sand, water has a huge capacity to store heat.
The steam in the air holds the heat close to the ground like an invisible giant blanket and prevents it from spreading into the atmosphere. Air with high humidity also needs more energy to heat up, which means more time for that energy to dissipate and the surroundings to cool. As a result, the lack of moisture in deserts allows these arid places to heat up quickly but also cool quickly.
Despite such rapid temperature changes, desert animals are well adapted to the extreme temperature changes of the desert.
"The biggest challenge is getting enough food and water to survive," said Dale DeNardo, an environmental biologist at Arizona State University who specializes in desert animals.
Reptiles are known to be the most abundant and diverse group of animals in the desert, adapting well to extreme temperature fluctuations because they are cold-blooded, meaning they don’t need to invest energy to maintain them. stable body temperature. Many reptiles also benefit from being small, which allows them to find cool nooks during the day or warmer rocks at night.
However, large hot-blooded or heat-collecting mammals, such as camels, are too large to escape the sun and unable to let their body temperature drop. Rather, camels exist by maintaining a constant body temperature in both hot and cold conditions. They do this by having multiple layers of insulation in the form of fat and thick bristles, preventing them from absorbing too much heat during the day and losing too much at night.
In contrast, desert birds use evaporative cooling - they use water to transfer heat out of the body, the same way humans sweat and dogs breathe - through a variety of different methods. (Some vultures urinate on their feet to cool down).
Plants that are more vulnerable to extreme temperatures face a much greater challenge since they cannot move. That is why iconic desert trees such as cacti have developed a variety of defenses, such as thorns and poisons, to protect their precious water resources from predators. hunt.
However, freezing temperatures at night can cause plant death because the water freezes and expands in their tissues, which can cause irreversible damage. As a result, plants grow only where the air temperature does not drop below freezing for more than a few hours per night, known as the icy zone.
