The hot and humid city

It’s bloody warm these days and our cities are not built for this. Homes are constructed to keep the heat in during winter. In the light of accelerated climate change which intensifies the extremes, our homes are becoming hot-boxes rather than comfortable spaces to escape from the heat of the outdoors.

Each summer I find myself worrying about the heat. What will the future bring? Will my city remain livable? I read about places where the temperature and humidity are so high, that cooling down via sweating isn’t an option anymore. This has to do with wet-bulb temperature. It is the lowest temperature a given surface can reach via evaporative cooling. The maximum potential temperature drop via evaporative cooling is calculated by taking the difference between the dry- and wet-bulb temperatures. Where dry-bulb is the actual temperature of the air.

A quick way to estimate this potential cooling is by using an adaptation of the rule of thumb calculation proposed by J. A. Knox et al. By subsituting the dewpoint value with relative humidity. Where we assume dewpoint decreases by 1 degree for every 5% drop in relative humidity.

Resulating formula:

T_wet = T_dry - ((100 - H_rel) / 3) * 0,1

Where:

T_wet -> wet bulb temperature T_dry -> actual air temperature H_rel -> relative humidity (%)

Using values of today:

T_wet = 32 - ((100 - 51) / 3) * 0,1 T_wet = 32 - 1,6 T_wet = 30,4

Which gives my body a whopping cooling potential of 1,6 degrees