Saturday, May 8, 2010

Heat Stress and Climate Change in India

After staring some more at the map of current wet bulb temperature maximums from Thursday's discussion of Shepherd and Huber, I made the above more focussed version of the map, just looking at Asia.  Again, this map shows the typical annual maximum for the wet bulb temperature TW, 1999-2008.  The scale coloration is slightly confusing, but it looks to me that that band in northern India and Pakistan already reaches wet bulb temperatures in the low thirties (equivalent to the low nineties fahrenheit).  So, if the basic framework of the paper is correct, a few more degrees Celsius of climate change will push this area over the threshold into having regular heat waves that are generally fatal for workers.  That could easily happen by mid-century even under central estimates of the climate sensitivity (3oC for a doubling of CO2).

I wanted to find evidence for this viewpoint from other sources, as independent confirmation that Shepherd and Huber are on the right track. So I looked around for papers that would provide more specific information.  I came across a report entitled Vulnerability to Heat Stress, Scenario of Western India, by Nag et al of the Indian National Institute of Occupational Health which is a non-profit research institute in Ahmedabad, Gujarat state. The main body of the report is an investigation of heat stress of manual laborers in four facilities in Gujarat and Rajasthan states.

The following map (from Maps of India) shows the states of India, and if you stare at it for a while and compare to the map up above, you can see that the hottest parts of Gujarat, and especially Rajasthan, are in the zone of interest, though probably parts of Pakistan and states like Punjab and Uttar Pradesh are even a little worse. Along with a portion of the Amazon, these are the regions of highest wet-bulb temperatures in the world today.  Gujarat and Rajasthan appear to fall into the region where the annual maximum wet bulb temperature is about 30oC or a little above, and thus about 3-5oC short of the mark where being outside for a number of hours would be generally fatal.

I have mixed feelings about the Nag et al report. On the one hand, it provides lots of useful data, and was clearly a great deal of work, and I'm grateful to have any scientific information at all about a fairly poor region of a developing country. At the same time, key information is missing in a number of places that makes it a little hard to evaluate exactly what the data in the paper mean.  I would kill to get my hands on the raw data. Still, overall, the report serves to confirm the impression from the Shepherd and Huber paper.

I am going to focus on just one of the study sites in the Nag report, which was a quarry in the Jodhpur region of Rajasthan, which had the highest environmental temperatures of the four.  The following photo montage from the report gives a feel for being a quarry worker in this part of the world.  Note the shelters used in the hottest parts of the day.

Nag et al say:
A very comfortable aeration in the shelter is the only solace for the workers to spend 2 to 3 hours each day, to cope against solar heat.
Another set of pictures is here:

(I don't know about you, but I'm profoundly grateful I wasn't born into that life).

During the study period, May-June 2009, the normal (dry-bulb) temperature ranged from 36 to 43oC (97oF-110oF) and that relative humidity was 50%-80%.  We aren't told how that compares to the regional climate generally, but the Wikipedia reports:
The climate of Jodhpur is generally hot and arid but with a rainy season from late June to September. Although the average rainfall is around 360 millimetres (14 in), it is extraordinarily variable. In the famine year of 1899, Jodhpur received only 24 millimetres (0.94 in), but in the flood year 1917 it received as much as 1,178 millimetres (46.4 in).
Temperatures are extreme throughout the period from March to October, except when monsoonal rain produces thick clouds to lower it slightly. During these periods of heavy rain, however, the generally low humidity rises and this adds to the normal discomfort from the heat.
So the study period may not have been the worst case wet-bulb temperature.  On the other hand, it appears that these guys are working outside in the sun, except during the hottest parts of the day when they use the shelters (or perhaps for periodic rests - it is unclear).  That can't be helping.

Before going further, we need to introduce yet another kind of temperature. The wet bulb globe temperature (WBGT):
The Wet Bulb Globe Temperature (WBGT) is a composite temperature used to estimate the effect of temperature, humidity, wind speed (wind chill) and solar radiation on humans. It is used by industrial hygienists, athletes, and the military to determine appropriate exposure levels to high temperatures. It is derived from the following formula:

WBGT = 0.7Tw + 0.2Tg + 0.1Td

  • Tw = Natural wet-bulb temperature (humidity indicator)
  • Tg = Globe thermometer temperature (measured with a globe thermometer, also known as a black globe thermometer, to measure solar radiation)
  • Td = Dry-bulb temperature (normal air temperature)
Temperatures may be in either Celsius or Fahrenheit
So this is a kind of composite temperature designed to measure the range of heat inputs to the human body.  Note, however, that one can potentially stand a higher WBGT than the same numerical value of wet-bulb temperature - if the globe temperature and the dry-bulb temperature are significantly higher than the wet-bulb temperature, then sweating helps. To give some feeling for the scale here, I found the US Occupational Safety and Health Administration regulations for US workplaces on heat stress.  These "are based on the assumption that nearly all acclimatized, fully clothed workers with adequate water and salt intake should be able to function effectively under the given working conditions without exceeding a deep body temperature of 38°C (100.4° F)". The Threshold Limit Values are as follows (expressed in WGBT terms):
You can probably already guess that this Indian quarry would not meet with the approval of American regulators...

Indeed, Nag et al took WGBT measurements during the study period and found these values:
I've circled the 5% and 95% percentile values of the distribution of WGBT's.  Unfortunately, they don't break out the components of WGBT, so we can't compare directly to the Shepherd and Huber paper, but certainly the conditions are way outside OSHA tolerance (of course, there's probably lots of migrant farmworkers right here in the US working in conditions not too far from this, but I imagine that reflects lack of enforcement).  So the question is whether the OSHA standards are simply way too prissy?  Or is working in these conditions actually pretty dangerous?

The Nag et al report answers that fairly clearly.  For example, they took data on the core temperature of the workers:

Again, I have circled the 95th percentile core temperature, which is 40.7°C (105.3° F).  That is seriously dangerous territory:
Heat stroke occurs when person’s Tcr rises above 40oC, as a result of impaired thermoregulation. High Tcr, cardiovascular stress, intravascular coagulation may result in cell damage in vital organs, such as the brain, liver, and kidneys, leading to serious medical emergency. Death may occur due to cardiac failure or hypoxia, or it can occur days later as a result of renal failure due to dehydration. The neurologic impacts of heat stroke include headache, dizziness, which can be followed by loss of consciousness, or other complications. Heat stroke patients may suffer a recurrent or continuous seizure activity, with risk of brain damage. The victims must receive immediate treatment to replace blood volume and electrolytes, and bring the T down to 39°C or below.
So at least a percentage of these workers are in serious trouble.  And indeed, Nag et al had the workers complete a questionnaire about heat effects they had experienced.  The results were as follows:
I have highlighted the Rajasthan quarry in blue, and some of the more serious heat symptoms in red.  Unfortunately, the report doesn't say what period of time the workers were instructed to consider in their answers.  In principle the period could be anything from "today" to "for the entirety of your work life".  I'm guessing it means "this year" or something like that, but we really don't know.

But what is clear is that a fairly high fraction of workers are experiencing serious heat symptoms: a third feeling faint, a quarter losing consciousness altogether, half experiencing mental disorientation, and one sixth experiencing seizures. It is hard to be as precise as I'd like, given the limits of the information available, but it does seem fairly clear that this is a population of workers that is quite close to the edge of what is physiologically possible in terms of doing manual labor outdoors.  It's inconceivable that this quarry will be operating in this manner in a world that is 12°C hotter than today, and likely that even a few degrees of warming would force it to close in the hot season, or else operate in a different manner.

In fact, looking at the table above, if Indian workers had any reasonable health and safety protections this quarry would be closed tomorrow.  However, even assuming that the quarry is allowed to continue to operate with little or no concern for the health of its workers, it appears that a few degrees of warming would likely cause productivity to drop sharply as the workers start keeling over more and more frequently.

Of course, the quarry has options.  The OSHA regulations above mention the possibility of ice vests as a way to bring hot workplaces into compliance by allowing workers to keep their core temperature down.  That seems like something that could be done in a pretty low-tech way suited to a developing country.  Alternatively, as India continues to develop, the quarry could become more mechanized and have the workers in air-conditioned cabs of machines. Still, the vast bulk of the Indian rural population works outside doing manual labor.  In the northernmost states that butt up against the Himalaya it appears that many of them must be up against the limits of their thermal tolerance, like these quarry workers.  It's hard to see how this can change quickly.

Prime Minister Manmohan Singh might want to rethink his reported opposition to firm and binding climate change targets.


David said...


This post well and truly indicates the problems with 3rd world dealing with climate change as well as providing an improvement in the standard of living facing PO and CC.

In many respects the folks at the quarry have not enjoyed the benefits if a high consuming fossil fuel lifestyle. Yet many will pay the price.

Many in the 3rd world see the problem created by 1st world. But which will be paid by them.

If we are to move towards a global solution to the impasse that exists then we need to get pretty creative. Some how we need to break the prisoner's dilemma approach we currently have.

Tom Bennion said...

Tunnelers have a lot of experience with these issues. Here is comment form my Dad, a retired civil engineer, talking about a 5 km rail tunnel.

We had a lot of experience in working in high temperatures in the Kaimai Tunnel.We used a measure called 'effective temperature' which took into account wet bulb and dry bulb temperatures and also air velocity. We cut down working hours from 8 to 6 at 27 degrees effective and then progressively to 3 hours at 30.5 degrees above which we were prohibited from working without permission from Mines Dept. Note that the effective temperature is at 100% humidity and zero airflow or the equivalent. A more typical situation for us would have been 29 degrees wet bulb and 60 metres per minute airflow giving an effective temperature of 27 degrees rising to 32 degrees wet bulb and 60 metres per minute airflow giving an effective temperature of 30.5. Bear in mind that we are talking about people working, not lying in a darkened room during siesta time. Our actual temperatures got well above this, of course, which is why we had to refrigerate. The figure quoted in the article of 95 degrees F (35 degrees C) wet bulb makes sense as a level above which there is a potential for distress and possible heat stroke. Fortunately, the condition of 100% humidity and zero airflow is extremely rare. Dry bulb temperatures in excess of this are quite common even now.

Stuart Staniford said...


Your father's effective temperature sounds like it might be similar to WBGT - the cutoff of 30.5 sounds similar to the OSHA limit of 30 for maximum limit for doing any heavy work.

dltrammel said...

Thank you for the details. Very informative. As someone who works at a physical job inside a building without air conditioning I can imagine the situation 10-20 years down the line. Its not going to be pretty. I wonder, do you think companies will shift to nighttime manufacturing to cut down on the effects of daily heat on workers and equipment?

Stuart Staniford said...


Yeah, I would guess that would be the response in some cases.

Gideon said...

I am Gideon. I am doing my Masters at IIT Madras in construction technology and management. I came to Godhra, Gujarat where LnT is constructing the Halol-Godhra-Shamlaji road project. The condition of workers here is more pathetic than those shown in the pics by Nag et al(2009). There is no proper drinking water facility and no shade for workers. I am working on developing a fluid replacement schedule for workers. I also referred to the US army technical bulletin on heat stress. The US Army has fluid replacement and work/rest schedules for its soldiers working in hot climates. But in India, there does not even seem to be any regulation fo rthis. The national building code talks a little bit about this, but still it is not specific to road construction.


Stuart Staniford said...


Thanks for your comment. I'm inspired that you're working on this. Hopefully as folks like you, and like Dr Nag, become more aware of the issue, India will start to develop standards and an enforcement mechanism for them.

Dr MP Cariappa said...

To get back to Jodhpur , the temperature yesterday was a documented 47.8 degrees Celsius.... at noon. And there are workers out there ,who have no choice but to work , for their family to have a meal.... For us in the military, we can attempt to enforce training restrictions, but what about those on outdoor guard duties ?? Climate change is really a major threat to our society today.. acclimatization to heat is not possible after a certain level of heat ....

himanshu said...

Yeah, I would guess that would be the response in some cases.