Final answer:
Increased susceptibility to dehydration as a pilot in hot temperatures is largely due to dry air at high altitudes, which accelerates water loss from the body. Humidity affects body cooling, with high humidity inhibiting sweat evaporation and low humidity potentially causing quicker dehydration and discomfort.
Step-by-step explanation:
As a pilot, flying for long periods in hot summer temperatures increases the susceptibility of dehydration because the dry air at altitude tends to increase the rate of water loss from the body. Low humidity at higher altitudes can lead to increased evaporation of moisture from the skin and the respiratory passages. Moreover, the body cools itself through the evaporation of sweat, which is less efficient in humid conditions; however, at higher altitudes where the air is drier, this process is more effective, potentially leading to quicker dehydration if fluids are not adequately replenished.
The expression "it's not the heat, it's the humidity" is relevant in this context. High humidity inhibits the evaporation of sweat, which is our natural cooling mechanism, making us feel hotter at a given temperature. Conversely, lower humidity, characteristic of higher altitudes, while it aids in cooling can also cause discomfort and increase the risk of dehydration and respiratory infections due to excessive drying of mucous membranes.