Effect of Wind on UHI

When thinking about the UHI from a physical perspective, it’s not surprising that one way to remove a mass of warm air from a system is to just move it somewhere else. Arnfield (2003) also suggests that an increase in wind activity will result in a decrease in UHI intensity primarily due to the fact that the warm air is moved away from the heat source and is replaced by cooler rural air. 

The main issue with Urban regions is that they don’t respond to atmospheric stimuli in the same manner as rural regions. Most weather stations are placed on rural land to avoid being contaminated by UHI alterations, which means temperatures, humidity and wind activity are archived without significant influence by the UHI. The UHI does scale with overall climate warming though, as a warming climate will evenly warm urban and rural regions by a similar margin. This also means wind speed measurements are optimistic (Appear faster than they actually are) as they don’t account for urban obstructions. The wind speed would vary depending on where it is being experienced within the city meaning some congested regions may have urban thermal plumes whilst others cool by unhindered winds.

In urban regions, wind is obstructed by all of the unnatural alterations to the landscape. High buildings, narrow streets, crevasses and such. This means that wind activity will be weaker and less efficient at removing the warm air from the system as seen in figure (1). It has also been suggested by Kershaw et al., (2010) that emphasis would need to be placed on urban morphology, wind speed and cloud cover during the summer evenings, whereas in the winter, the system is mainly controlled by large scale climate. 

Obstructions to wind cause a region of turbulent flow, which both slows the wind and weaken the transfer of air. Source

Wind speed does play a large role at mitigating the UHI but the degree of UHI depletion is inversely proportional to the morphology complexity. This could be taken into consideration as a mitigation strategy during urban development by being conscientious about flow patterns and obstructions. Of course, this does rely on meteorology to solve an anthropogenic formation, which to some regard is a very green approach, but also unpredictable and not necessarily reliable. 

As a final side note, the obstructions do have their benefits. During stormy weather, they weaken the gale force winds and lower the risk of objects being hurled into the air under steady streams of winds. Some thought may need to be put into the geographical climate of a region before a decision to welcome unhindered wind pathways into a city is made. 

In all honesty though, I was pretty excited when I was warned to be wary of cats falling out of the sky whilst I still lived in Plymouth. You'd be surprised what strong winds can lift into the air. The real questions we can pose: Do I wish to remain cool and refreshed in the summer breeze? Or perhaps feel safe walking around without a titanium umbrella? Maybe consider moving somewhere less windy...