Wet Bulb Globe Temperature: it’s cooler in forests, really

Don’t you find it cool?

As a part of citizen science, Kanagawa Prefecture asks people in Kanagawa to measure “How hot it is” in our home prefecture. They lend us a compact WBGT monitor and ask to report how WBGT number went up at 13:00 every Friday during August. I joined the troop of this fun and have carried the monitor wherever I’ve been during August. Reporting duty is only for Friday at 13:00 and the rest of the time we can just check WBGT number to (yeah) “confirm how hot it is now!”

WBGT monitor.
It’s in “indoor” mode so that
radiation temperature is not calculated.
(Please see below.)

First, I have to explain WBGT. It’s acronym for Wet Bulb Globe Temperature. This NOAA site explains what is WBGT nicely. Or, this site by Japanese Ministry of Environment explains Japanese version for how to read the numbers. (US uses Fahrenheit and Japan uses Celsius.) Anyway, it’s calculated with this formula:

WBGT =

0.1 * Temperature (that we normally find) + 0.7 * Humidity + 0.2 * Radiation Temperature (measurement of heat radiated by things surrounding the monitor, sun included)

The nice thing for this measurement is it somehow quantify the effect of power of heat and humidity our body receives. Japan is very humid country and the same 30°C can have larger damage here than in the other part of the planet where the air is drier. With global warming we in Megalopolis Tokyo feels more vulnerable to frequent heatwave. Having an indicator that can warn us dangerous level of atmospheric heat is very helpful to protect ourselves. That’s the rationale for the Prefectural Government soliciting our citizen’s help to feed the database. Our report will be consolidated nationwide by CCCA NIES (Center for Climate Change Adaptation, National Institute for Environmental Studies of Japan).

Damned hot August day in a park near sea.
 Certainly, there was a sea breeze.

By walking around with the monitoring machine, I realized it is indeed very helpful to decide the contents of activity based on the WGBT number. I also confirmed the magic of summer forest in numerical term. It’s damned hot this august in Yokohama. The WGBT monitor regularly shows higher than 31°C outside in towns, which is at the critical level. Kids should not engage in outside activity under that condition, and sedentary senior citizens could be killed just by sitting or sleeping in such environment.
 

Around 18:00 in my mom’s garden, one day this August.
 WGBT’s still 27°C which is at
 “very dangerous” temperature for vigorous outdoor activity.
In NOAA’s term, it is recommended to have
 at least 40 minutes of rest after one hour of outdoor.
 Understandable.

The story is different in forests. During one weekend mowing in Niiharu Citizen Forest when the activity was under the shade of forest trees, we did not feel that much strenuous for carrying powered grass cutter. The WGBT stayed 25-26°C for 10:00-12:00. Gosh. According to NOAA, it was the level if our operation had been under the direct sunlight, it could have been OK to take 15 minutes break for every one hour. (So we did.) Our experience matched with this recommendation. The life within forest is indeed cooler at least in Kanagawa Prefecture.

This is a measure taken one day in
Yokohama Nature Sanctuary (my post on January 22, 2015)
at around 13:00.
With the temperature and that much humidity,
WGBT 28.5 was thanks to the trees surrounded my lunch,
 I guess.

I also measured WGBT on the bank of Yadoriki Stream at 13:00. It was only 21.7°C. The point had approx. ASL 600m and it was a bit cloudy lunch time. I guess heat radiation was subdued thanks to the clouds. Yet, even with more than 90% of humidity the place was definitely easier place to enjoy outside lunch. Ahhhhhhhhhhhhhhhhh, a stream of pure and cool water and deep mountain forest ... Let’s go to forest during heatwave and nurture our forest.

 Lots of families enjoyed a cool weekend in Yadoriki Stream.

If you find environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/