- Who
- Dhahran, 8 July 2003
- What
- 35 degree(s) Celsius
- Where
- Saudi Arabia (Dhahran)
- When
At 3 p.m. on 8 July 2003, the city of Dhahran in Saudi Arabia experienced a dewpoint temperature of 35°C (95°F) accompanied by a dry-bulb air temperature of 42°C (108°F). This resulted in a total heat index (aka apparent temperature, or the temperature “it feels like” to the human body) of 81.1°C (178°F).
The dewpoint is one method of measuring humidity, which when factored together with the air temperature as measured by a thermometer can give a more accurate sense of how hot it feels (aka the heat index). It represents the temperature when air, at a given atmospheric pressure, reaches saturation point and can no longer hold on to moisture; at this stage, water vapour condenses into its liquid state, which can lead to the formation of cloud, fog and even precipitation. The dewpoint never exceeds the air temperature; if the dewpoint temperature is equal to the air temperature, then relative humidity is 100%.
The higher the humidity, the harder it is for the body to sweat and cool itself down and a. A dewpoint of 35°C (95°F) is considered to be the upper threshold of what humans can endure for anything more than a few hours. Such conditions are exceptionally rare, but are becoming more likely as the climate warms.
The Persian Gulf, on which Dhahran sits, is renowned for its extreme humidity levels, as are the Red Sea and the Gulf of Aden that surround the remainder of the Arabian Peninsula. A similar extreme heat event was recorded in the Iranian port city of Bandar Mahshahr (at the north-west end of the Persian Gulf) on 31 July 2015, when the dewpoint hit 32.2°C (90°F) and the heat index soared to 73.8°C (165°F). It’s believed that even higher dewpoint temperatures are likely to occur over the water in this region, but these have not been measured owing to the fact that it requires having the right equipment in the right place at the right time.
