Pakistan's Deadliest Heat Wave on Record Kills at Least 800

The death toll from a brutal heat wave in Pakistan rose to 830 on Wednesday, making it Pakistan's deadliest heat wave in recorded history. Most of these deaths--at least 770--occurred in Pakistan's largest city, Karachi. According to statistics from EM-DAT, the International Disaster Database, Pakistan's previous deadliest heat wave was in 1991, when 523 people died.

Death Tolls from the 5 Deadliest Heat Waves in Pakistan's History
1) 2015: 830+
2) 1991: 523
3) 2014: 248
4) 2003: 200
5) 1953: 111


Figure 1. Pakistanis receive ice outside a hospital during heatwave in Karachi on June 24, 2015. A state of emergency was declared in hospitals. Image credit : RIZWAN TABASSUM/AFP/Getty Images.


Figure 2. Temperatures in Karachi, Pakistan from June 11 - June 24, 2015 show that the heat wave peaked on June 20, with a high temperature of 112.6°F (44.8°C.) The heat index was as high as 121°F.

The worst of the heat is over for Pakistan
The past week saw an unusually long string of very hot days with temperatures that did not cool off at night in Pakistan. The heat wave peaked on Saturday June 20, when the high temperature hit 112.6°F (44.8°C) in Karachi; the heat index peaked at a dangerously high 121°F. According to the Pakistan Meteorology Department, Karachi's all-time high temperature was 118°F (47.8°C) on May 9, 1938. A tropical depression associated with the approaching southwest monsoon pushed ashore along the border of Pakistan and India on Tuesday, bringing thunderstorms and cooler weather. Wednesday's high reached only 98°F in Karachi, breaking a streak of six consecutive days when the temperature hit 103°F or higher. The previous longest streak of 103°F+ temperatures during the past fifteen years was three consecutive days, which occurred most recently in 2006. Temperatures failed to dip below 85°F at night during the streak of 103°F days over the past week; very warm nights are associated with high mortality during intense heat waves, since there is no chance for the body to gain an overnight respite. High temperatures are expected to rise to 103°F again in Karachi on Thursday, but then cool to the upper 90s over the weekend--about ten degrees Fahrenheit cooler than last weekend's temperatures. The cooling rains from the southwest monsoon are likely to arrive in Karachi by mid-July, and the circulation associated with the monsoon should insure that the region will not see any more temperatures this summer as high as were recorded last weekend. If the death toll from the 2015 Pakistan heat wave rises above 1,030, it will join this year's May 2015 heat wave in India as one of the ten deadliest heat waves in world history.


Figure 3. Progress of the monsoon towards Pakistan as of June 23, 2015 (green line) has been about a week slower than its usual pace. Karachi, Pakistan usually sees the monsoon move through during the second week of July. Image credit: India Meteorological Department .

A deficient monsoon predicted, but above-average rains so far
The atmospheric circulation patterns brought on by an El Niño event usually cause much reduced monsoon rains in India. With the current moderate El Niño event is forecast to intensify this summer, the India Meteorological Department (IMD) is forecasting only a 7% chance of near-average rains during the 2015 summer monsoon period, and a 93% chance of below average or well below average rains. IMD's best estimate is that 12% less rain than usual will fall. However, during the first half of June, monsoon rainfall was 11% above average for India as a whole.

Climate change and the monsoon
This year's deadly heat waves in India and Pakistan were made much more probable by the fact that Earth is experiencing its hottest temperatures on record--the January - May 2015 period was the planet's hottest such period on record. The planet's record heat contributed to unusually warm ocean temperatures off the coast of Pakistan, which were about 1°C (1.8°F) above average this week. Warmer oceans make hotter heat waves over adjoining land areas more likely. 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 and Pakistan with climate change is drought, though. Many climate models show that climate change might increase the average rainfall in India and Pakistan 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.

Jeff Masters