“Heat Waves: They will become hotter, more frequent, last longer, and occur in more varied places.”

By Dr. John J. Hidore

When it seems unusually warm someplace there is a tendency to describe it as a heat wave. The reason is simple. Normal high temperatures vary greatly from place to place. So what would be defined as a heat wave in one location would not be appropriate for another location, perhaps one not too far away. An adequate definition might be, “A heat wave is an unusually warm or hot period lasting for days or perhaps weeks.”

We associate heat waves with summer, but by this definition they can actually occur at any season. India and Pakistan make a clear definition of a heat wave and they use different temperatures in different parts of the country to establish what constitutes a heat wave. In the plains regions temperatures above 40 C (104F) constitute a heat wave. They also define a severe heatwave for this region as experiencing temperatures over 46 C (114.8F).

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Western European Heat wave of 2019

The last two decades have seen the hottest summers in the last 500 years.The summer of 2019 was no exception. July of this year was the warmest July ever recorded for the planet. Record high temperatures were recorded over much of western Europe in the last week of July. In Paris, France the temperature reached 110°F ( 43°C ) on July 25. In Bayreuth, Germany the temperature reached a record 93°F (34°C). A high of 105 °F (41°C ) was recorded in Belgium. The high temperatures became a health hazard, particularly for the elderly.

It was the lack of air conditioning and the high temperatures which were largely responsible for the high death toll in Europe in the summer of 2003. The use of air conditioning varies greatly from country to country. Over 90% of households in Japan and the United States have air conditioning systems. There is relatively little installed air conditioning in households in Europe. In Germany, for instance, less than two percent of households have air conditioning systems. Parts of Paris are served by a cold water pipeline system that uses water from the Seine River for cooling.

Indian heat wave of 2016

India experienced unusually high temperatures in 2016. Temperatures were above normal most of the spring. Normally, the hottest months of the year are April, May, and June, before the summer monsoon rains begin. In May a severe heat wave alert was issued for several states. A severe heat wave is one in which temperatures of at least 117°F (47.2°C) occur. In the city of Philodi, in western India unofficial temperatures reached 124°F (51°C). This is the highest temperature on record in India. Temperatures averaged above 104 ºF (40°C) over large areas. Some urban high temperatures were:

New Delhi 47 °C (117 ºF)
Churu 50 °C (122 ºF)
Philodi 51.°C (124 ºF)

The impact on the country was immense. More than 300 million people were adversely affected. Crops failed or were below average in 13 states in the last growing season . Thousands of farmers abandoned their farms. In places the asphalt on the streets partially melted. At Bikaner, the streets were being sprinkled with water to reduce the heat. Some 17,000 villages had, or were facing water shortages. Several Indian states shut down schools to reduce risk to students. Heatstroke was a widespread problem and many deaths were reported across the region. Fortunately the government responded in a variety of ways to reduce the suffering and mortality.

Asian heat waves of 2015

In 2015 a May heat wave in India claimed at least 2,500 lives. Heat waves are fairly frequent in India but this was the greatest loss of life from a heat wave in over 30 years. Extremely high temperatures were reached in cities scattered over the country. Power outages were wide spread as a result of high demand for air conditioning. The city of Khammam recorded the highest temperature ever recorded there at 48 degrees C (118.4 degrees F). Other high temperatures that were recorded were:

Allahabad 47.8 C (118.0 F)
Delhi 45.5 C (113.9 F)
Hyderabad 46 C (115 F)
Jharsuguda 45.4 C (113.7 F)

In June the deadliest heat wave known to have occurred in Pakistan took place in the southern part of the country near Karachi. The death toll is unknown for certain, but may have reached more than 1000. It followed by several weeks the severe heat wave that struck India. The heat wave struck during the month of Ramadan which made the impact of the event more severe than it might have been. Unfortunately, city services were not in condition to cope with the heat.

Perhaps the most deadly heat wave of the 21st Century was that which occurred in Europe in August of 2003. Temperatures in France reached as much as 40°C (104F) and remained exceptionally high for two weeks resulting in nearly 15,000 deaths in that country alone. The death toll over Europe reached 35,000 at least and may have been as high as 50,000. A large contributing factor in the high death toll was warmer nighttime temperatures. Nighttime temperatures were much warmer than normal. As a result people without air conditioning could not cool down during the night. The heat stress accumulated over time.

Extreme heat waves also can devastate agriculture. In Europe in the heat wave of 2003 temperatures averaged 5.5°C (10°F) above normal. In Italy corn yields dropped 36% below average. In France fruit yields fell 25% and wine production 10%. Heat also affects the rate of plant pollination.

As the planet warms it can be expected that: (1) there will be more severe heat waves and (2) They will become hotter, more frequent, last longer, and occur in more varied places. New record high temperatures will be set for the planet As cities grow larger in area and population they will also experience increasing heat waves.