Earth's 5th Deadliest Heat Wave in Recorded History Kills 1,826 in India

The death toll from India's horrid May heat wave has risen to 1,826, making this year's heat wave the second deadliest in India's recorded history--and the fifth deadliest in world history. According to statistics from EM-DAT, the International Disaster Database, India's only deadlier heat wave was in 1998, when 2,541 died. With over 400 deaths recorded in just the past day and the heat expected to continue over India for another week, the 1998 death toll could well be exceeded in this year's heat wave. However, death tolls from heat waves are very difficult to estimate, since excess heat is typically not listed as the primary cause of death in cases where the victim has a pre-existing condition such as heart or lung disease. For example, the U.S. National Climatic Data Center (NCDC) lists the total direct deaths from the U.S. heat wave of 1980 at 1,260, but estimates that the combined direct and indirect deaths (i.e., excess mortality) due to heat stress was 10,000. Below is the list of top ten deadliest heat waves in world history as compiled by EM-DAT, the International Disaster Database, which uses direct deaths for their statistics, and not excess mortality.

The 10 Deadliest Heat Waves in World History
1) Europe, 2003: 71,310
2) Russia, 2010: 55,736
3) Europe, 2006: 3,418
4) India, 1998: 2,541
5) India, 2015: 1,826+
6) U.S. and Canada, 1936: 1,693
7) U.S., 1980: 1,260
8) India, 2003: 1,210
9) India, 2002: 1,030
9) Greece and Turkey, 1987: 1,030

Note that the EM-DAT database may not be entirely reliable; for example, they list no heat deaths in the U.S. for the 1988 heat wave, while the U.S. National Climatic Data Center (NCDC) lists 454 direct deaths and 5,000 combined direct and indirect deaths. The 2010 Japanese heat wave, which EM-DAT gives a death toll of 170 for, disagrees with the 1,718 total from the Ministry of Health, Labour and Welfare of Japan. Weather records researcher Maximiliano Herrera alleges that the deadliest and most brutal heat wave Chinese history, in Eastern China in the summer 2013, had thousands of deaths which were not reported by the Chinese authorities. The official death toll was merely 40.


Figure 1. A young Indian child pours water on himself as he tries to cool himself off in New Delhi on May 28, 2015. Image credit: MONEY SHARMA/AFP/Getty Images.

It's the heat and the humidity
Temperatures across much of India have been 5°C (9°F) above average this May, with very high humidity. In many of the hardest-hit areas of eastern India, the heat index dropped below 100°F for only four hours each night for several consecutive days this week. This sort of day-after-day heat stress is very hard on vulnerable people, and leads to high mortality. For example, in Channai (Madras) on May 24, the high temperature reached 108°F and the heat index topped out at 123°F, and never dropped below 97°F the entire day. Far more extreme heat index values have been observed in some areas. For example, on May 23 at 14:30,  Bhubneshwar recorded a temperature of of 42.2°C (108°F) with a dew point of 29.3°C (84.7°F), giving an astonishing heat index of 62°C (143.6°F.) According to weather records researcher Maximiliano Herrera, a heat index of up to 65°C (149°F) has been measured at some stations in eastern India during the heat wave.


Figure 2. Progress of the monsoon towards India as of May 28, 2015 (green line) has been close to its average pace. If the monsoon follows its usual pace, it will move through the province hardest hit by this year's heat wave, Andhra Prahesh (shaded in yellow), by June 5. This province recorded 1,334 heat deaths as of May 29, 2015. Image credit: India Meteorological Department .

The monsoon is coming
This is the time of year when India's 1.2 billion people look beseechingly southwards, toward the advancing southwest monsoon. The monsoon's arrival brings rains that cool India's scorching May heat, and the monsoon's rains give life, providing 70 - 80% of the year’s total rainfall in just four months. The India Meteorological Department (IMD) is forecasting that the arrival of the southwest monsoon at the southern tip of India will occur this weekend, on May 30. This is two days ahead of the average arrival date, June 1. The monsoon should move through the province hardest hit by this year's heat wave, Andhra Prahesh, by June 5. However, IMD is also forecasting a roughly doubled chance of below-average rains during the summer monsoon period, and predicts only 91 percent of the usual rainfall will occur. The problem: the atmospheric circulation patterns brought on by an El Niño event usually cause much reduced monsoon rains. The current borderline weak/moderate El Niño event is forecast to intensify this summer, and this is likely to cause a significant reduction in monsoon rainfall over India. According to EM-DAT, the International Disaster Database, more than 4.2 million people died in India between 1900 - 2014 due to droughts from failed monsoon rains, primarily during El Niño years. The five worst Indian monsoons for rainfall deficit:

1) 1877, -33%
2) 1899, -29%
3) 1918, -25%
4) 1972, -24%
5) 2009, -22%

Up until the late 1960s, it was common for the failure of the monsoon rains to kill millions of people in India; the 3-year drought that began during the strong El Niño event of 1965 killed at least 1.5 million people. However, since the Green Revolution of the late 1960s--a government initiative to improve food self-sufficiency using new technology and high-yield grains--failure of the monsoon rains has not led to mass famine in India. For example, the fifth worst drought in India's history occurred in 2009, but did not result in serious food shortages--and neither would a similar failure of the monsoon this year. However, a weak monsoon could affect India’s fragile power supply, since the country is heavily dependent on hydropower. In 2012, a weak monsoon forced farmers to use huge amounts of power to pump groundwater to make up for lack of rain. The resulting strain on the power grid helped trigger a blackout that affected 600 million people. Fortunately, many reservoirs in India are above their 10-year average level heading into the summer.

Climate change and India
This year's deadly heat wave in India was made much more probable by the fact that Earth is experiencing its hottest temperatures on record--the past twelve months were the warmest twelve-month period in recorded history, and so was the January - April 2015 period. According to the India Meteorological Department, a warming climate increased heat waves in India by a third between 1961 to 2010. As the planet continues to warm due to human-caused global warming, heat waves will become more frequent and more intense, and heat-related deaths will soar unless we take strong measures to adapt. An April 2015 paper published in Regional Environmental Change, Intensification of future severe heat waves in India and their effect on heat stress and mortality, warned that "heat waves are projected to be more intense, have longer durations and occur at a higher frequency and earlier in the year. Southern India, currently not influenced by heat waves, is expected to be severely affected by the end of the twenty-first century." Perhaps a bigger concern for India with climate change is drought, though. Many climate models show that climate change might increase the average rainfall in India from the monsoon, but when dry years occur, the hotter temperatures accompanying the dry years will drive much more intense droughts capable of causing significant challenges to growing food in India.

Links
The May 27, 2015 post by Eric Holthaus of Slate discusses the India heat wave and climate change.

Wunderground's climate change blogger Dr. Ricky Rood wrote a nice 3-part series about the challenges India faces due to climate change after he completed a 2009 trip there.

Bob Henson will have a new post on the Texas/Oklahoma flood situation on Friday evening or Saturday morning.

Jeff Masters