by P. Homewood, May 6, 2019 in NotaLotofPeopleKnowThat

This study aims to estimate the affect of urbanisation on daily maximum and minimum temperatures in the United Kingdom. Urban fractions were calculated for 10 km × 10 km areas surrounding meteorological weather stations. Using robust regression a linear relationship between urban fraction and temperature difference between station measurements and ERA‐Interim reanalysis temperatures was estimated. For an urban fraction of 1.0, the daily minimum 2‐m temperature was estimated to increase by 1.90 ± 0.88 K while the daily maximum temperature was not significantly affected by urbanisation. This result was then applied to the whole United Kingdom with a maximum T _min urban heat island intensity (UHII) of about 1.7K in London and with many UK cities having T _min UHIIs above one degree.

This paper finds through the method of observation minus reanalysis that urbanisation has significantly increased the daily minimum 2‐m temperature in the United Kingdom by up to 1.70 K.

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.896

As ever, the real issue with UHI is the change in the effect over time. Has, for instance, the effect of UHI increased in London and other cities increased over the last century, or was it just as great in 1919?

What we do know is that, generally speaking, towns and cities have both expanded over time, and seen increasing development in terms of roads, buildings, traffic and economic activity.

Indeed, these same tendencies also apply in small towns and what may appear to be relatively rural sites.

We also know that many of the sites used by the Met Office in their UK temperature series are urban and airport locations.

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https://www.metoffice.gov.uk/public/weather/climate-historic/#?tab=climateHistoric

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