The 2018 summer season in Seoul was very hot and unexpectedly long. Temperatures rose to 39.6°C, the highest temperature ever recorded in 111 years across the history of meteorological observation. In the same year, the number of days of heat waves measured at 35, the highest in 75 years, since 1943. The number of tropical nights also lasted 26 days, the longest recorded since 1973.
Looking at the changes in summer temperatures in Seoul, the average temperature (on a 10-year average) in the summers from 1908 to 1917 was an average of 23.2°C, but 100 years later, from 2008 to 2017, this average increased by about 1.8°C to 25°C. Summer days have increased significantly since the 2000s. The average number of summer days between 2001 and 2010 (the number of days of the year where the maximum daily temperature is above 25°C) was 122 days, lasting about four months. In addition,  this number increased to 136 days in 2016. The Korea Meteorological Administration (KMA) predicted that in the second half of the 21st century, the average temperature in Seoul will rise by an additional 5.2°C to reach 40°C, due to the influence of climate change.
One characteristic of the rise in Seoul's summer average temperatures is that it includes a rise in the lowest temperatures which are measured at night. In 2016, the average number of tropical nights in Korea was 10.8 days, but Seoul recorded 32 days, with this figure being three times more than the national average. In particular, the number of tropical nights in Seoul was 32 days, which is eight days longer than the number of heat wave days (24 days). 
The number of tropical nights in Seoul has steadily increased, unlike the number of heat wave days. It is inferred that tropical nights have been affected by Seoul’s increasing rate of urbanization, unlike heat waves which are closely related to weather phenomena. Because of the changes in space due to urbanization, Seoul has become vulnerable to high temperatures and heat waves, due to factors such as the reduction of heat absorption sources, the increase of artificial heat emissions, the decrease of wind speed, and  the increase in solar energy storage.
The number of patients with heat-related illnesses increased 2.1 times nationwide in 2018 compared to 2016, while that of Seoul increased 3.7 times. Heat waves can lead to death as well as heat illness. Furthermore, it is a weather disaster that can cause massive casualties. The number of excess deaths caused by the heat wave is twice that of other weather disasters. Particularly, the more urbanized the areas, the greater the number of deaths caused by the heat wave. In terms of population characteristics, the elderly and the disabled are the most vulnerable to heat waves.
In order to examine the heat wave response policies that citizens desire, a survey was conducted among Seoul citizens to investigate their awareness of heat wave special warnings, precautionary measures when facing heat waves, and desired other policies. In response to the question about the place where people feel most uncomfortable during heat waves, the general public responded that outdoor activities and public transportation are inconvenient, with the locations listed by priority: sidewalks, downtown areas, and bus stops. On the other hand, citizens who are vulnerable to heat waves said that staying at home at night was the most uncomfortable.
According to a survey on the ranking of heat wave response policies that Seoul citizens most desire, 54.9 percent of the respondents said they would benefit from a reduction in electricity rates. This policy was also followed by policies that would secure shade for outdoor spaces such as street trees (47.7%), improve heat wave shelters (41.9%), and the provision of additional resources for citizens vulnerable to heat waves (37.5%). Except for national policies such as the lowering of electricity rates, the demand for policies to expand shady areas such as street trees and shade screens ranked the highest.
Citizens' safety knowledge varied greatly depending on their attitude toward heat waves. Citizens should respond to the heat wave with the attitude of "I desire to protect my body myself," and the Seoul Metropolitan Government should not merely support citizens who are vulnerable to heat waves, but also improve the city's environment to cope with heat waves. In particular, to cope with the heat waves at the urban level, improvements guided by a thermal environment management strategy should be implemented throughout Seoul. With the basic strategic goals of "not releasing heat, not storing heat, not receiving heat," these measures to improve the heat environment should be applied to the city’s infrastructure, buildings, outdoor spaces, and so on. To this end, the Seoul Metropolitan Government should lower urban heat by expanding street trees which provide sufficient shade, improving the cooling of subway stations, and create local air cooling stations, such as those which spray water. In addition, the Seoul Metropolitan Government's internal cooperation system should be established to effectively manage the urban heat environment and most effectively respond to heat waves.