There will be more severe heat waves. They will become hotter, more frequent, last longer and occur in more varied places.
By Dr. John J. Hidore
February 12, 2019——Heat wave is a general term. When it seems unusually warm someplace there is often a tendency to describe the weather as a heat wave. As it turns out it is very hard to define a heat wave. The reason is simple. Normal summer high temperatures vary greatly from place to place. What would be defined as a heat wave in one location would not be appropriate for another location, perhaps not even 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 them with summer but by this definition they can actually occur at any season.
At least one country makes a clear definition of a heat wave and that is Pakistan. India also defines heat waves and uses different temperatures in different parts of the country to establish what constitutes a heat wave. In the plains regions of the Unites States, temperatures above 40degreesC (104 degreesF) constitute a heat wave. They also define a severe heat wave for this region as experiencing temperatures over 46 degreesC (114.8 degreesF).
Distribution of the 2018 Heat Waves
In 2018 the northern hemisphere experienced major heat waves. Heat waves occurred over most of the northern hemisphere as well as Australia. Europe experienced a major heat wave in the spring and summer. These extreme heat waves were largely a function of climate change, particularly of global warming.
Global warming also increases the probability of higher extreme temperatures during a heat wave. Such was the case in 2018. All-time highs were recorded in North America and Europe. At one location in Finland that is north of the Arctic circle, a temperature of 33.3°C (92°F) was recorded. Undoubtedly extreme highs were recorded in many other areas as well. Qurayyat, in Oman, experienced a 24 hour period when the temperature did not drop below 42.6°C. This was the highest minimum daily temperature ever recorded.
The Impact of the Heat Waves
The impacts of the heat waves were many and varied. They included:
A. Increased mortality: Japan, Algeria, and Canada recorded fatalities attributed to the heat.
B. Droughts and agricultural losses. In parts of Europe precipitation amounts fell to as little as 20% of normal.
C. The closing of nuclear power plants due to a shortage of water for cooling.
D. Frequent and severe wild fires. Severe wild fires occurred on every continent except Antarctica.
E. In 2016 and 2017 there was major bleaching of the Great Barrier Reef. In all probability 2018 will turn out to be the same
F. In the summer at one point the combined concentration of greenhouse gasses reached 500 ppm, approximately 100 ppm above the average for this time.
The Deadly Heat Wave of Europe in 2003
Some heat waves have become deadly. 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 (104 DegreesF) and remained exceptionally high for two weeks resulting in nearly 15,000 deaths in that country alone. The death toll over Europe reached approximately 35,000 and may have been as high as 50,000.
A large contributing factor in the high death toll was warmer than normal nighttime temperatures. 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.
Asian heat waves of 2015
That year 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 degreesF). Other high temperatures that were recorded were:
Allahabad 47.8 degrees C (118.0 degrees F)
Delhi 45.5 degrees C (113.9 degrees F)
Hyderabad 46 degrees C (115 degrees F)
Jharsuguda 45.4 degrees C (113.7 degrees 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. 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.
As the planet warms it can be expected that: (1) there will be more severe heat waves. They will become hotter, more frequent, last longer and occur in more varied places. As cities grow larger in area and population they will experience increasing heat waves. (2) new record high temperatures will be set more frequently on the planet.