UHI and Tmin Nanaimo

Yesterday I posted a WUWT article about Tmin in the UK rising 1.7C thanks to UHI.

I ive near Nanaimo BC and here is the graphs for Tmin and Tmax since 1947.

Tmax has barely changed. Tmin is up 2C or more. UHI.

Data from Weatherstats and Environment Canada

UHI in the UK raises Tmin by 1.7C

UHI causes Tmin go  up by 1.7C in UK

The observed increase in T min can be attributed to an increased intensity of the UHI during the hours after sunset and into the night. Many studies have previously shown that UHII is maximised during the night (Arifwidodo and Tanaka, 2015; Montávez et al.2000; Ripley et al.1996). The intensity is maximised during these hours, as heat absorbed by urban structures will be re‐radiated back into the atmosphere at a slower rate, due to smaller sky views, than natural structures. Further, the increase in impervious surface in an urban area causes a reduction of the latent heat flux and a rise in the sensible heat flux (Zhou et al.,2014). This leads to a difference between the rates at which the urban and natural area will cool during the night, with urban areas sustaining a higher temperature into the night. With minimum temperatures often occurring at night, the slowed rate of cooling in urban areas results in an increase of the observed minimum temperature.

Read it all here


National Post Tries to Scare Canadians – And Fails If you Look Carefully

National Post has published some maps claiming Canada is going to suffer from “scorching summers”.

I’ve hit my online paper article limit so I’ll post the tweet.

The animated gif starts with a scary January, lots of red. And article/tweet predicts “warm winters, scorching summers”.

Note that they are using “mean temperatures”, not maximums.

But if you capture the monthly images , when do you notice about the summer months?

June/July/Aug are not scary and all red. They are pretty high up on the scale (which means the lowest change)


And I repeat. This is mean temperatures. Not max. And having looked at the data I know many of the BC cities have a very low rate of maximum change versus minimum.

It is the minimums that are climbing in a lot of cities and the max isn’t.

Here is my original hometown of Kelowna. Tmax has barely changed since 1900 (and in fact dropped from 1900 to 1950 and then climbed a bit since then.

The ratio of Tmin change to Tmax change is 10.8 to 1. Look at the Tmin climb. Huge. 7C warmer.