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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
31 Mar 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Natural Hazards and Earth System Sciences (NHESS).
Extreme heat in India and anthropogenic climate change
Geert Jan van Oldenborgh1, Sjoukje Philip1, Sarah Kew1, Michiel van Weele1, Peter Uhe2,7, Friederike Otto2, Roop Singh3, Indrani Pal4,5, and Krishna AchutaRao6 1Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands
2Environmental Change Institute, University of Oxford, Oxford, UK
3Red Cross Red Crescent Climate Centre, The Hague, Netherlands
4Columbia Water Center, Columbia University, New York, New York, USA
5Climate Central, Princeton, USA
6Indian Institute of Technology Delhi, New Delhi, India
7Oxford e-Research Centre, University of Oxford, Oxford, UK
Abstract. On 19 May 2016 the afternoon temperature reached 51.0 ºC in Phalodi in the northwest of India, a new record for the highest observed maximum temperature in India. The previous year, a widely-reported very lethal heat wave occurred in the southeast, in Andhra Pradesh and Telangana, killing thousands of people. In both cases it was widely assumed that the probability and severity of heat waves in India are increasing due to global warming, as they do in other parts of the world. However, we do not find positive trends in the highest maximum temperature of the year in most of India since the 1970s (except spurious trends due to missing data). Decadal variability cannot explain this, but both increased air pollution with aerosols blocking sunlight and increased irrigation leading to evaporative cooling have counteracted the effect of greenhouse gases up to now. Current climate models do not represent these processes well and hence cannot be used to attribute heat waves in this area.

The health effects of heat are often described better by a combination of temperature and humidity, such as a heat index or wet bulb temperature. Due to the increase in humidity from irrigation and higher SSTs these indices have increased over the last decades even when extreme temperatures have not. The extreme air pollution also exacerbates the health impacts of heat. From a health impact point of view, the severity of heat waves has increased in India.

For the next decades we expect the trend due to global warming to continue, but the cooling effect of aerosols to diminish as air quality controls are implemented. The expansion of irrigation will likely continue, though at a slower pace, mitigating this trend somewhat. Humidity will probably continue to rise. The combination will give a strong rise of the temperature of heat waves. The high humidity will make health effects worse, whereas decreased air pollution would decrease the impacts.

Citation: van Oldenborgh, G. J., Philip, S., Kew, S., van Weele, M., Uhe, P., Otto, F., Singh, R., Pal, I., and AchutaRao, K.: Extreme heat in India and anthropogenic climate change, Nat. Hazards Earth Syst. Sci. Discuss.,, in review, 2017.
Geert Jan van Oldenborgh et al.
Geert Jan van Oldenborgh et al.
Geert Jan van Oldenborgh et al.


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Short summary
On 19 May 2016 a temperature of 51.0 ºC in Phalodi (Northwest India) set a new Indian record. In 2015 a very lethal heat wave had occurred in the Southeast. We find that in India the trend in extreme temperatures due to greenhouse gases is largely cancelled by increasing air pollution and irrigation. The health impacts of heat waves do increase due to higher humidity and air pollution. This implies that we expect heat waves to become much hotter as soon as air pollution is brought under control.
On 19 May 2016 a temperature of 51.0 ºC in Phalodi (Northwest India) set a new Indian record....