Threshold (28-29 deg) of "deadly" days are actually optimum in Thailand

Further to the reported onslaught of "deadly" hot weather in the tropics, I show here a J-shaped plot of Thai Central valley hot season death rate vs. maximum daily temperature. We note that the least deadly temperature is about 33-34. This translates to an average daily temperature of about 28-29. The death rate increases about ten percent when daily Tmax hits the upper 30s. These data are all-age, elder rates reportedly are optimum at lower temps.

When we think that many deaths occur at the end of a long lingering illness we should ask whether hot-weather induced tipping point death should be considered a heat-related death rather than in many cases a benign heat-accelerated death.

And why doesn't anyone mention the threat so close to the heart of most tropical people, namely more frequent cool weather?

The association between temperature and mortality

in tropical middle income Thailand from 1999 to 2008

Benjawan Tawatsupa & Keith Dear & Tord Kjellstrom &

Adrian Sleigh

Global risk of deadly heat Camilo Mora, Bénédicte Dousset, Iain R. Caldwell, Farrah E. Powell, Rollan C. Geronimo, Coral R. Bielecki, Chelsie W. W. Counsell, Bonnie S. Dietrich, Emily T. Johnston, Leo V. Louis, Matthew P. Lucas, Marie M. McKenzie, Alessandra G. Shea, Han Tseng, Thomas W. Giambelluca, Lisa R. Leon, Ed Hawkins & Clay Trauernicht

Nature Climate Change 7, 501–506 (2017) doi:10.1038/nclimate3322

Threshold for "Deadly" days

The Nature paper (referenced last entry) determines the threshold for "deadly" days by sifting through and classifying various reported heat wave events  in places like France and Southern Australia and comparing them to days with "ordinary weather" in the same place, using a classification technique ("support vector machines") that aims to draw boundaries between types of events based on what appear to be discriminatory boundaries between attributes. In this case it is found with only a fair degree of reliability that heat-attributed deaths generally occur on hot days, with a lesser impact from high humidity. Notably unsurprising conclusions.

By picking points from the chart I developed a simple linear relationship (shown above in green) that emulates the "deadly" boundary. It also appeared to me (as an old psychrometrician) that the boundary appeared to correspond fairly well to a wet bulb temperature of about 26, at least when humidities are 70 percent or more, which is usually the case in Bangkok. Given the broad approximations of the method the study dictates that on days with usual hot-season humidity in the tropics the average daily temperature becomes "deadly" at about 29 degrees.

Readers of this blog might recall that this is the temperature where I turn on the bedroom air conditioner at night. Readers who have some experience with wet bulb and global wet bulb temperatures will be aware that military training and sports practice are thermally acceptable at wet bulb temperatures of 26, heading into precautionary modes only above Twb=26.

Global risk of deadly heat: Bangkok compared

Publication of this paper "Global risk of deadly heat" in the prestigious Nature Climate Change journal last week 

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3322.html

has created a considerable stir. It concludes that a deadly increase in tropical health problems is a likely outcome following man-made global warming.

How well does this hold up for Thailand? This question will be examined here starting with this brief entry showing the results of the Nature study (right) compared to recent years including the record (?) 2016 in Bangkok (left).

Following this study, almost all days in the Bangkok hot seasons (March-June) for the past few years would be categorized as "deadly", that is, they are hotter than the red line which is meant to divide various historical heat waves with and without fatalities. With humidity typically 70 percent, it follows from this study which draws from a global database (not specific to Thailand or other tropical regions) that average daily temperatures of higher than about 27 deg should be classified as "deadly". This line also corresponds closely to a wet bulb temperature of 26. Is this suggestive of fatalities? How does this compare with observations here in Thailand over the past few years, both personal and published by local researchers? Or with standards developed for military training and sports internationally?

The hot season broken by moisture

Mid-May dawn: with the coming of rainy and cloudy weather, the back of the hot season seems to be broken, with dawn temperatures below 30 degC (86F) in my downtown neighborhood. At the peak of the hot weather a couple of weeks back they were consistently over 30. 

Notice the 28-30 temps downtown and the 27 or so further out including the Don Muang airport area where our long-term records are. This agrees with my previous study indicating a 2-3 deg "heat island effect" in the Sukhumvit area.

Afternoon Bangkok sun blasts glassy condos

In an earlier post we showed how anyone seeking a "view condo" pays the penalty of terrible heat either in the morning (east facing) or afternoon (west facing). Curtains, blinds, or dark glass don't help much, they just heat up to 50 deg C (130F) and act like ski-cabin radiators. Ugh! Few of us think of this when we buy a condo, we are charmed by views which become minor considerations after we occupy a condo for a few weeks.

Be warned! Air conditioning does not alleviate this radiant heat problem!

Netatmo shows local heat island effect in Bangkok

This is a mix of select data showing you local differences in dawn temperature. On the recent right side you can see several sources superimposed. My condo Netatmo outside temp (brown) is the highest, probably because of all the walls and concrete that surround the sensor. The yellow points from the Planetorium are very similar, suggesting that the Sukhumvit area overall has a generally elevated temperature probably from urban heat island effects, about +3 C degrees heating.

Red points are Don Muang data, for which I have long term data, and green points from Korat, higher elevation and upcountry, generally 2-3 deg lower than Bangkok. The new airport at Souvanaphoum is also a little lower than Don Muang; it's further out of town.

Notice how last year the morning low at Don Muang was over 30 for several days. No such days this year at Don Muang, so last year's peak was a little worse, because the rains came a little later. (Sukhumvit area is this year is over 30, only because of +3 deg heat island effect). I had earlier expected this year to be worse by comparison, but that was before I realized that my Netatmo local readings were boosted by urban heat island warming.

If I want to estimate Don Muang dawn temperature from my Netatmo data I should subtract 3 deg. These corrected values are also plotted here shown as blue points.

So we have just now this week hit the probable high point in discomfort for 2017. To me it was suffocating. I found myself turning on the aircon all the time. My pub mate Al, exactly my age: "I never complained about the heatt here before, but this year it really hit me." We both thank clouds and rain that are now pulling the dawn temperature down into the mid 20s.

But even now today I am turning on aircon on arriving home at the end of the day, after 6 pm.

Glass condos: good way to throw away money and suffer at the same time

So when you buy a west or worse east facing condo with those big glass walls that are fashionable now in Bangkok (Wow! Look at that view!) you don't think of the expense and years of misery you are taking on. But let's start with my glass door to a small veranda exposed this month to morning sun from about 8 to 11 am. Here are the calcs for refrigeration capacity and expense. A sunny morning heats the curtains to about 50 C, which then serve the same function as hot water radiators. To offset this added heat I need a dedicated 26000 BTU split air conditioner unit, it barely provides the needed 10 kw of cooling power (2.6 kw electric power). So maybe you need two such units for this small room?

But you have plenty of money, so problem solved!

No, not at all. When you look at that curtain on waking up, you are looking not at a 25 degree cooled wall, but at a 50C heating panel, and though the room air may be 25 C, you are feeling that blast of radiant heat, as unwelcome on your face and body as it might be welcome in a northern ski lodge.

I will claim that it is not possible to live comfortably in such an environment, being driven from bed every morning because of solar heating via windows, regardless of air conditioning and curtains, blinds, etc which do little to prevent heating in the room, especially radiant heating from interior window coverings (or tinted windows). But anyone who has ever parked a closed car in the sun knows this already! 

A fiery April ascendancy of the sun

A noon without shadows, April 26

Now at the end of April last week the sun reached its noon zenith over the city of Bangkok. The morning 6 am temperature never dropped below 30 C -- possibly a record high in an era of ascending thermal discomfort. The temperature on my bedroom air conditioning thermostat, hardly ever different than the 29 C that drives me to flip the switch on at night, actually now tends to read 30 C, a level I never remember seeing before. My neighbor's walls are slightly cool to the touch, about 27, indicating that they, to my benefit, are using their air conditioning, holding room temperatures to about 25 which is the usual here in Thailand (though the government is trying to get people to raise their set temperatures to 26.)

Creeping heat shown by Netatmo module station 17th floor condo.

6 am temperatures on Sukhumvit,
Bangkok over the past 10 days

Based on a 50-year stay in Thailand and study of long-term records I have concluded that the dawn (6 am) temperature is the best indicator of hot season discomfort for the coming day. This just broke through the 30 degree C level this Sunday morning, a rare event, for the first time this year, portending some major hot weather during the peak of the hot season over the coming three weeks. (Maximum sun exposure will be this coming Friday but the greatest discomfort arrives a couple of weeks later, unless we have a strong and early onset of rains). Over the past few decades there has been a very fast rise in hot season dawn temperature, 2 degrees since the late 1970s, reflecting both urban heat island effect from pavements etc but also probably an ominous long term land warming throughout Thailand. The consequences of a continuing trend at this rate over the next 20 years are almost unthinkable —  the doom temperature is said to be about 35.

Meanwhile those of us living in our Bangkok condos and apartments must cope with this difficulty. Even now for some, this means full air conditioning 24/7, typically two to four split unit compressors whirring away, 12 hours a day, as much as 50,000 baht a month. For many systems this produces an unpleasant clammy coolness because the on-again, off-again operation of the typically oversized condo units set to temperatures of 25 or less accumulates interior humidity reaching as much as 80 percent or more. Not comfortable!

A moderate amount of adaptation by owners and smart use and scheduling of the machinery can cut this power use and cost by as much as three quarters or more. My own bill for a typical month is less than 1500 baht and our condo is just as comfortable as our neighbors' who have the big bills of 15k baht or more.

Given the current rate of increased warming in the city, this is an excellent time to experiment a bit, both to economize and to set better standard practices for the coming generation who are expanding the use of air conditioning. I will follow up later this week with another post setting forth specific steps aimed at improved comfort at much reduced cost — with continuing use of air conditioning when it is really needed.

Netatmo map this morning predicts daily discomfort

We approach (in 7 days) the maximum direct solar heating of the year at latitude 13.75 (BKK) with the prospect of encountering this year the "most sweltering year in Bangkok ever", which case I will argue later. But for now, notice today that the dawn temperature, which I claim is the singlemost important indicator of perceived heat for the day, is about 29-30C( 84F) according to the excellent Netatmo weather map, which includes my own dawn reading of 29C (84F). Today is likely to be "the worst heat" for a long time from the human point of view. Although it has been claimed in the scientific literature that the hot season daily minimum temperature is higher in the big city than in rural areas, this fresh data from this morning suggest otherwise.

If you dread tropical discomfort, look only at the 6 am temperature. More than 29C (84F) and you are not going to be happy unless you can find either aircon or more wisely local spots of radiant cooling at say T=25 (79F) or less.

Only when we go far afield and higher elevation do we get the reduced early am temperature, as at Nakhorn Ratchasima, where I have my farm. The data suggest (to my surprise) that heat island effects may not be as important as often believed.

Fan at low setting cuts heat discomfort by four degrees

This graphic is from a study by Joseph Khedari done in Thailand with Thai students. With humidity in Bangkok in the hot season at 70 percent or more, we see that comfortable temperatures range from about 27C with no fan, up to 32 degrees with a fan air velocity of about 1 m/s. This applies to a person sitting at work with no shirt and a fan blowing on the face at about 1 meter distance, which I find refreshing -- more so than air conditioning. An overhead fan works too (I am sitting under one as I type this entry) but only if there is not a pocket of hot air lurking above near the ceiling.

Take a bath in front of the whole neighborhood

That's what my wife does in her Southern Thai village, doesn't think a thing of it, carrying on several conversations at once. The Thai bathe at least twice a day, and in all the years -- more than 50 -- I've been here, I've never smelled a single case of B.O., even on crowded buses in the heat of the afternoon in Bangkok. Remarkable how at the end of a hot day, everyone's shirt seems as freshly pressed as in the morning.

It was a shock to move from Thailand in 1963 to England, where many people bathed once a week. Standing in line next to nice English ladies one day at Sainsbury market, I actually thought I might be downwind from the cheese department.

Bangkok hot season: coolest spot around

Almost everyone is amazed at the coolness of the sky, shown here as 16 degC (61F) on a hot humid Bangkok day (dew point 25C) when the air temperature is in the nineties (34 C). If we go up country a bit we will find it's even hotter but the water vapor will be lower and the corresponding radiant temperature of the day and night sky as low as freezing point,  0 deg C! Our sense of how hot it is where exposed to the sky (but preferably in shade) will be a compromise between radiant temperature of all the objects around us (sky above at 16 degrees and land below the horizon which here is about 34 degrees) and the air temperature. In other words clear sky exposure, out of the direct sun, helps comfort.

But the main benefit of a cool sky is to cool the ground surface at night time. Locally the moisture in the air and cloudiness are the main factors that affect this night ground cooling, with dry clear sky promoting cooling by roughly 100 watts per square meter. By comparison, the effect of raised CO2 levels in the atmosphere is less than 2 watts per square meter, though this effect is near-global and not easily reversed. The great uncertainty about human-caused global warming is the interaction between CO2 and water vapor. If CO2 promotes higher atmospheric humidity then its greenhouse effect is much amplified. This is difficult to model, hence the uncertainty in estimated impacts.

Complex thermal comfort data needs colorful solutions!

Operating a bedroom air conditioner to get the best comfort at the least cost is a lot more complicated and non-intuitive than most of us (including me) have imagined. Netatmo plus the visual SQL display tools from Tableau are the only way to really understand what is going on here in this "simple" display of thermal comfort data in a single night in steamy Bangkok March 2017 which we will examine in more detail later.

We thought that keeping the bedroom door closed to "keep the heat out" and "not waste electricity" was the best policy but the data here suggest otherwise!

Truly, the delight is in the detail!

Bangkok destined to be unliveable? Ominous trend from Netatmo

I am neither a "warmist" or a "denier" as they call those who are inclined to a group ideological approach to the subject of global warming. And I know from paleoclimatic studies that global changes occur naturally and plausibly via contemporary and excess human energy use. But I find reason for worry with the data shown here. Notice the daily high temperatures for the hot season (April and May) do not seem to have increased much if at all over the past 60 years of record from the Don Muang airport. But I have never thought that daily highs are of great significance. after all, Tucson gets a lot hotter in the day.

But look at daily Bangkok low temperature, usually at or about dawn, over the span of the last sixty years. In contrast to maximum daily hot season temperatures which everyone talks about, daily minima are not much recognized as being of importance, though I claim that these daily low numbers represent, at least in the tropics, the best index of thermal stress on human and perhaps other life. The coincidence of high dew point temp, surface sea temp in the Gulf of Thailand, and thermal comfort level through the day really determine the level of discomfort and danger, and these indices follow closely the daily Tmin during the hot season (April and May) in Bangkok. We see here a marked trend for hot season Tmin (only April and May data shown here) with values rarely exceeding 26-27 back in the fifties, but now commonly at 30 or more. Big difference!

As I write, Bangkok residents, Thai and non-Thai, have found conditions barely tolerable in the past few weeks of early May, 2016, many people remarking that it has been "the worst ever". Those of us who have lived through it would not disagree with my claim, backed by theory and experience,  that a daily morning min of about 35 degrees would be intolerable to human life without some kind of air conditioning. So our thinning margin of safety might be said to be half of what it was when I first came to Thailand in the 1960s.

But we should not rush to claim that this is due mostly to greenhouse gasses. Temperatures here and many places are airport temps, and airports have progressively become embedded in hundreds of square miles of mostly concrete, creating the well-understood effect of urban heating. The other morning, with 7 am temps of the pavement of 34 degrees in my neighborhood on Thonglor, you might say we were already having a local doomsday, though the minimum official airport temp for that day did not exceed 31.

How to distinguish between heating from urbanization and from global warming? I think I see away to do that and will make a project of it.

Temporary heat blips from direct sun

You probably don't want to place your Netatmo outdoor module where it will get direct sun. This yellow anomaly below is caused by direct morning sun for and hour or two on the outdoor module, and probably to a lesser degree from heating of the dark brown soil on which the module is set in this case. 



Poor location! Better put the module out of the sun and on a less heat absorbing surface.

Radiant heat: invisible but deadly

On a warm afternoon with full sun a darkish thin surface (such as a metal roof or a tile roof) heats up to 50 degrees C or more, with the heat being almost immediately transferred undiminished to the underside, as you can see from the temp reading of the underside of this rubberized canvas tent which is supposed to provide cooling shade, but really provides heating shade, which will radiate on the order of (52-32)*5=100 watts per square meter to your head, plus perhaps as much again convected to the air below. Not as bad as the 700 watt sun, you might say, but not comfortable either – and suffocating if the underside of the roof is not radically ventilated. So next time you are sitting under one of these tents at a Thai wedding or funeral, be warned -- it's the heat, not your emotions, that is causing you to feel like you are going to faint.


Here is an excerpt from the manual of the Australian company Bluescope Steel who make (and promote) steel roofing in Thailand. This indicates a reduction in heat transmission through thin roofs (steel, cement tile, etc) if they have foil insulation, properly installed (air space above and below foil, and foil with shiny side down.) For a dark roof, the thermal transmission is said to drop from 165 to 22 watts, almost 90 percent. But I can say from my own experience that there are many qualifications to this supposed effectiveness of thin foil, more specifically that bubble-backed foil that comes in rolls, to be discussed later with a real example.

Hot Season brings miserable hot wet wind from the sea

Much like the Texas Gulf, onshore hot season wind smothers Bangkok with heat and humidity. Even at the coolest time of the day the saturated air from the gulf to the south is close to 29C (surface sea temp, red), so sweat at body temperature will provide little cooling.

Old time hot days in Boston

From the free download chapter

We are much inclined to think that air conditioning is a necessity, but I have to wonder these days whether this and much of the other technology said to be so wonderful is really important at all. I think of the days old people in Boston used to call scorchers, though my mother preferred the ancient term dog days. On those canicules my grandmother would take me on the streetcar from her walk-up South Huntington Avenue apartment in Jamaica Plain downtown to the Boston Common. I still enjoy looking at the details in this photo, the necktie, the newspaper. Was this man a bum? An unemployed veteran? If so, he made an effort to dress properly. Or was he just a lower paid adjuster from one of the insurance companies that dominated the skyline, lacking in those days even the first John Hancock building behind the Boston Common? 

My Thai wife in her bedroom not minding 29 C (84F)

Generally I have not put much credibility on theories of racial differences for thermal comfort. My Thai wife's comments, sweat thresholds, and complaints are very close to my own. But as the hot season closes this year in I notice that I am turning on the aircon every night when the temp hits about 29 C (84F). She is not. Be interesting to see when she does.

My Netatmo readying for the coming blast of heat

With seriously high temperatures last week forcing me to turn on the aircon for sleeping, I ready my Netatmo system for the expected record blast of heat next month.

Hot season relentlessly moving in. New records for Bangkok?

@Netatmo @dickmeehan Checking out my Netatmo gear for the coming heat. Perfect performance to date, looking forward to recording rich data in and outside my Bangkok condo tropicalcool.com

Fire up the Netatmo, the heat is coming!

Weather unsettled of late, Bangkok breaking free of the cool northerly breezes and succumbing to the steady southern winds off the steamy Gulf of Thailand (once known as the Gulf of Siam). A bit of rain of late.


Thai wife turns on the aircon last night. Muttering on the streets of hot weather. Must fire up Netatmo and buy another module for the coming heat. 


If this usually reliable guy is right, could be an interesting year.