Urban heat release from vehicles, industry, buildings etc is only one contributor to the urban heat island effect. Others include the reduction of surfaces for evapotranspiration (because of impermeable roofs and paving) and the 'canyon effect' with tall buildings.

I believe that the urban heat that you refer to is just one contributing factor to the creation of a phenomenon (the Urban Heat Island). Absorption of solar short-wave radiation, air pollution, anthropogenic heat (from vehicles, industry, etc.), sky obstruction, waterproof surfaces and decreased wind speed can all contribute to modifications of the energy balance in cities and the creation of the UHI.

In Girona a city of Catalonia with 102000 inhabitants the maximum urban heat island with the method ofmobile transects is 12.1 C on 31 December 2007, 5 C in Deveses of Salt, 7.1 C in Juli Garreta Street, downtown of Girona.

I recommend you review this work https://yceo.users.earthengine.app/view/uhimap that shows the heat islands recorded by satellite of many cities in the world.

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Este trabajo, querido Pablo Sarricolea, ya lo he leído, y lo citaré en mi tesis, que espero leer este año. Un abrazo y gracias!!

Surface Urban Heat Island (SUHI) is not the same as Urban Heat Island (UHI)