Monday, November 28

Resolving the great debate of each summer: the dry heat of the interior or the humid heat of the coast is worse

Spain is on its way break the absolute record for heat waves and that can only mean one thing: the season of discussions about which heat is worse, the humid or the dry, begins. In other words, is the summer in Zaragoza or the summer in Valencia worse?

Do the inhabitants of Écija, the “pan of Andalusia”, complain of vice, with many degrees, but 15% relative humidity and what we should really fear is that Vigo with 29 degrees, but 85% humidity? I mean, are we going to the beach this summer or are we renting a little house in the driest place on the central plateau?

the eternal battle. The theme of dry vs. humid heat is one of the classics of summer. There is no doubt that there is a lot of personal preference here. Individual, community and social adaptations to a specific climate mean that some areas have better conditions than others to combat the types of heat to which they are most exposed. However, from a scientific point of view, the debate simply does not exist.

The body, the heat and us. The body is, essentially, a biological engine and, like any engine, it needs cooling systems so as not to become saturated. If we take into account that our basal metabolism consumes between 50 and 60 kcal/h/m2, we will realize that without this body cooling our temperature would increase one degree Celsius per hour. We would go into a ‘technical stop’ sooner than we can imagine.

In general terms (and, specifically, in humans) the regulation of our body temperature uses three fundamental systems to balance the heat that is produced with that which is lost.

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These three mechanisms are the thermoreceptors (located in the skin and in the preoptic nucleus of the hypothalamus), the thermoregulatory mechanisms (based on sweating and peripheral vasodilation) and what we could call the control area located in the brain (which is responsible for coordinating more complex “refrigeration” behaviors such as ‘turning on the air’, ‘getting in the shade’ or ‘going for an ice cream’).


When the heat comes… As soon as body heat exceeds certain thresholds, all systems are activated because an excess of temperature can cause significant damage to the body; our blood vessels dilate, we begin to hyperventilate, we get thirsty and feel an overwhelming need to escape the heat. Oh, and we started to sweat.

We must not forget about sweating because it is our main biological cooling system. But for this, as I say, the thermoregulation system must be able to identify that it is hot. In fact, the main cause of thermal ‘discomfort’ is not the temperature itself, but the thermal sensation.

Humidity is key. And it is that thermoreceptors not only use degrees Celsius to make a composition of place, but also take into account things such as the relative humidity of the environment. Why? Well, because, as I said, sweat is our main physiological tool to cool the body and sweat becomes less effective as the ambient humidity increases.

So much so that, at the same temperature, the sensation of suffocation is much greater with high levels of humidity (because the evaporation capacity is lower). It is about our body saying “be careful, in these conditions we will not be able to maintain the temperature for a long time”. Thus, for all practical purposes, 30 degrees with 90% humidity feels the same as 40 without it.

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So, dry heat or moist heat? As we can see, heat and humidity are two factors that interact with each other and in a very close way. This means that, at the same temperature, the lower humidity will always be preferable. However, the truth is that temperature equality does not normally occur. There is a reason why people spend the summer on the beach even though the humidity is higher: except on rare occasions, the moderating effect of the sea limits the maximum temperatures and makes the thermal sensation much better.

What is better summer in Zaragoza or summer in Alicante? Well, it depends, of course: but, as a general rule, heat peaks will be worse in Alicante and normal days will be worse in Zaragoza (thermal oscillation is greater and, for this reason, the days will be hotter). However, if we leave localisms aside, Spain has the perfect solution to resolve this eternal dispute between the inland areas and the coastal areas of the peninsula: the Canary Islands.

Image | Maarten Van Den Heuvel

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