What defines a desert is the large daily thermal amplitude. What amazes us about these geographical areas is that we have very high maximum temperatures and very low minimum temperatures during a single day. This phenomenon has a physical explanation.
The characteristics of the atmosphere and soil of deserts are responsible for this large daily temperature range. It all starts because the atmospheric air in desert areas has very little humidity. Because it has very little moisture, it is unable to retain heat. On the other hand, the soils of these climatic zones are very clear, vegetation is absent or very scarce. This causes its albedo, or the proportion of solar radiation that a surface reflects from everything that reaches it, to be very, very high. And this characteristic has the consequence that a lot of heat is dispersed into the atmosphere.
So what we find in deserts is that they lose a good part of the solar radiation that they receive because of these two physical characteristics, the low humidity of the air and the high albedo of the soil.
Furthermore, desert soils, which are sandy and arid, have the characteristic of heating up very quickly during the day and cooling down very quickly during the night. That is, they absorb a lot of heat quickly during daylight hours, which raises the temperature significantly, but they also expel that heat very quickly at night.
Having said this I must tell you that not all deserts are the same. We can distinguish between hot deserts and cold deserts. And these two types have different thermal dynamics. Not all deserts will have temperatures below 0°C, and not all will reach 50°C.
If we look at hot deserts, such as the Sahara (in North Africa), the Sonoran desert (United States and Mexico) or the Atacama desert (Chile), the latter only in the lowest areas, we see that during the day the temperature can easily exceed 40 °C and even reach 50 °C. For example, the maximum reliably recorded temperature is in Death Valley in the Mojave Desert (California, United States) with 54.4 °C, also a hot desert.
With sunset, however, temperatures drop very quickly compared to those reached during the day, but normally in these hot deserts they do not drop below 0 °C. At most they can reach -1°C, -2°C or -3°C. But of course, even if they do not reach very low temperatures, since the high ones are very high, they record daily temperature changes of over 40 °C. So if we find ourselves in a hot desert, what we have to worry about most is the risk of hypothermia at night, not because the cold is enormous, but because of the contrast of having been exposed to extreme heat during the day and suddenly dropping to a temperature of 40°C below.
If we talk about cold deserts such as the Gobi (Mongolia and China), the highest areas of the Atacama or Patagonia (Argentina and Chile), in summer temperatures can reach 30 or 40 degrees, even if not 50 °C. But at night the drop is very extreme and can reach polar values of -10 °C or -15 °C. The result is that in them we also find a large thermal amplitude. And in this case, if you find yourself in a cold desert at night, there is a risk of hypothermia due to low temperatures.
In summary, the answer to your question is that nights in deserts are cold, but they are much colder in cold deserts than in hot deserts, although in both there is a similar thermal amplitude during each day.
Emma GaitanShe is a physicist, an environmental doctor and head of the Meteorology and Climate Change area at the Climate Research Foundation.
Coordination and writing:Vittoria Toro.
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