The heat wave is on the rise. Heat wave alarms have been issued in most parts of the country, and most local daytime temperatures are rising to around 35 degrees. This weekend, the temperature will rise and the heat wave will hit its peak this summer. The temperature in Seoul on Saturday will rise to 37 ° C and Sunday to 35 ° C.

Heatwave often reminds us of Yeongnam, including Daegu. Last year (2018), the temperature in Hongcheon rose to 41 ° C on August 1, 2018, but the highest record ever recorded was 40 ° C in Daegu on August 1, 1939.

In particular, long-term temperatures indicate that Daegu has the highest temperature in Korea. Data from the summer's highest average temperatures during the 30 years from 1981 to 2010 show that Daegu's temperature is the highest in the country at 29.8 ℃. The second place is 29.7 ℃ in Jeonju and Jeongeup, and the fourth place is 29.6 ℃ in Uiseong. Gwangju ranked 11th at 29.3 ℃ and Hongcheon 12th at 29.2 ℃. Seoul is ranked 32nd at 28.4 ℃. Among the weather stations, the region with the lowest summer temperatures is Daegwanryeong, which has a temperature of 22.1 ° C (see figure below).
Then can we say that Daegu is the most severe heat wave area in Korea? Can we say that the Daegu and Gyeongbuk areas are more severe than the Gwangju and Jeonnam areas?

If you define and express the heat wave simply by the highest temperature, Daegu is the most severe area in the country. This is because the highest temperature in summer for 30 years is the highest in the country. However, the situation can be different if you consider other factors, such as humidity or insolation, when defining heatwaves. Considering the maximum temperature as well as humidity, the situation will be very different. If the humidity is high even though the temperature is the same, the stress caused by heat waves is much greater.

One example is the difference between a dry sauna and a wet sauna. In dry saunas where temperatures exceed 90 ° C, many people sweat more than 10 minutes. However, it is not uncommon for wet saunas to last more than 10 minutes at temperatures lower than 30 ° C. Simply considering the temperature, a wet sauna is not a heat wave compared to a dry sauna. But our bodies are under greater thermal stress.

Professor Yale University Michelle Bell and Dr. Huh Seul-gi have recently published an interesting study. When heatwave is expressed simply by using only the maximum temperature and when using the Heat Index that considers not only the maximum temperature but also the humidity, and also by using the WBGT that considers the maximum temperature, humidity and insolation, We analyzed how the days and duration of heatwaves and the heatwave area differed (Heo et al., 2019). This study analyzes how the heat wave characteristics can vary according to the heat wave index, a variable that defines and expresses heat wave. The team analyzed the four-year summer heatwave from 2011 to 2014.

The results showed that heatwave days varied significantly between stations using the highest temperature (Tmax), the thermal index (WBGTmax), and the thermal index (HImax). Most notably, when heatwaves are expressed based on the highest temperature, the number of heatwave days is high at Yeongnam station, but the use of heat index or heat index decreases the heat wave days at Yeongnam station while The number of days of heatwaves at stations has increased significantly (see figure below). The circle size of Yeongnam station is decreasing (reducing the number of days of heat wave) and the circle size of Honam area and Jeju station is increasing.
The intensity of heat waves in each region also varies greatly depending on what is used as the heat index. For example, in August 1, 2014, when the heat was severe, the heatwave region showed the most severe heat waves except for the east coast. However, if the heat wave is expressed by the heat index or heat index, Gangwon and Yeongnam The heat wave of fat is relatively weak. The heatwave area and intensity vary depending on what the heatwave is defined and expressed as a reference (see figure below).
The research team centered on the occurrence of heat illness caused by heat waves, and when the heat wave index is defined and expressed by considering the heat index (WBGT), the maximum temperature, humidity and insolation, the warning about heat waves is most appropriate and can be issued. It is emphasized that it can also be effective in preventing damage.

It is interesting to note that the Korea Centers for Disease Control and Prevention analyzed the patients with heat-related diseases that occurred last year (Park Sung-woo et al., 2019). The number of febrile patients was highest in 937 in Gyeonggi-do, followed by 616 in Seoul and 436 in Gyeongnam. However, there are 17.1 people in Jeollanam-do region, the most common in Korea, followed by 14.4 in Jeju Island, 13.1 in Gangwon and Chungbuk, and 12.9 in Jeonbuk and Gyeongnam. The highest temperature was 4.9 in Daegu, the lowest after Sejong. Gyeongsangbuk-do is 11.7, not the highest level (see the figure below).
Heatwaves are a complex disaster. It is true that the maximum temperature is convenient for defining and expressing heat waves and is actually a very important part of the heat wave, but the maximum temperature is not everything. Highest temperature is not a heat wave. Factors affecting heatwave include a variety of factors, including maximum temperature and humidity and insolation. Heatwave damage also depends on maximum temperature, humidity, insolation, and vulnerability. The current heat wave is based on the highest temperature. The heat wave can be defined simply as the maximum temperature, and there can be a big hole in preventing the damage caused by taking measures according to the maximum temperature.

<Reference>

Seulkee Heo, Michelle L. Bell, Jong-Tae Lee, Comparison of health risks by heat wave definition: Applicability of wet-bulb globe temperature for heat wave criteria, Environmental Research, 168 (2019) 158-170

* Sung-Woo Park, Hyun-Jung Cho, Soo-Jin Baek, Hyo-Soon Yoo, Kyung-Woo Woo, 2018 Operation of Emergency Room Surveillance System for Thermal Diseases, Day Health and Disease , Vol. 12, No. 20, 630-638