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What is the urban heat island effect?

Temperatures in the city tend to be a few degrees warmer than surrounding areas, but why?
Credit: WTLV

JACKSONVILLE, Fla. — Ever notice on hot summer days it is often a few degrees warmer in the city than surrounding rural areas? This is not an observation unique to Jacksonville either, but can be seen in most urban areas around the country and world. 

Check the latest forecast here. 

On the First Coast the difference in temperatures across our area can be attributed to local effects from the ocean and our many lakes and rivers, but another major factor is what we call the Urban Heat Island Effect and why during our summer months you probably notice it more often than you think.

The EPA (Environmental Protection Agency) describes it as "urban heat islands" occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat.    

This is thanks to darker surfaces often seen in cities ability to absorb more heat during the day in what we call a low albedo. An albedo is an object's ability to absorb or reflect light.  

For example fresh snow has a high albedo, meaning it reflects a lot of light and maintains its cold temperatures, while freshly paved blacktop absorbs light and thus heat, causing the temperature to heat up on and over those surfaces. 

That is why many new buildings especially in warmer climates are being built with light colored roofs to help supplement the effect of the urban heat island. 

Credit: WTLV

Another factor that you may see from time to time especially in the Jacksonville area is convective clouds on occasion build quicker over downtown and urban areas. This can be thanks to the ground in those areas heating up quicker and thus causing the air to rise and convective clouds to build. 

Just one more factor to take in to account when making a forecast and why if you ever want to escape the heat your best may be finding a nice green space outside of the city. 

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