Sample analysis
The sample temperature data box plot was drawn using SPSS software to analyze the distribution of the data (Figure 3). The results show that the sample data covered a range between 30–52°C and have a good spatial distribution. The interquartile range is 9°C, which accounts for 40.91% of the range, indicating that the temperature samples were not concentrated in certain intervals, but are distributed in various intervals, which ensures a sufficient number of samples in each interval. At the same time, the median was 42°C, indicating that the sample can better cover the heat waves above 35°C relatively well. Basic descriptive analysis shows that the samples can be used to study the effects of high-temperature heat waves on residents’ emotional health.
Correlation analysis between high temperature and emotional elements.
The correlation coefficient analysis between high temperature and emotional elements indicates that the correlation coefficients for high temperature and irritability, high temperature and hostility are positive, and the reliability test of 0.00 (Table 1) indicates that these two have significant positive correlation. The correlation coefficient of distress did not pass the reliability level test, but the segmentation correlation analysis of the original data according to the temperature found that the temperature of 35-38°C was positively correlated with distress, with a correlation coefficient of 0.309, and the test had a reliability level of 0.006; a negative correlation was found at 38-43°C with a correlation coefficient of -0.256, and passed the reliability level of 0.004 (Table 2). This shows that high temperature and distress are closely correlated.
The correlation analysis between high temperatures and emotional elements was studied through Grey correlation analysis. The results showed that the absolute correlation degree indicators of high temperature and emotional elements were irritability > hostility > nervousness > distress; the composite correlation degree index followed the sequence of nervousness > irritability > distress > hostility (Table 3). The absolute correlation index only reflects the similarity between the temperature and emotional elements curve and is similar to the correlation analysis calculation method. Therefore, the calculation results are similar, indicating that irritability and hostility have higher correlation, while nervousness and distress have lower correlation. However, the composite correlation coefficient reflected the complex relationship between the similarity of the curves and the closeness of the rate of change, so it is inconsistent with the correlation analysis and the absolute correlation degree, which indicates that nervousness and irritability also have a very high correlation. This close relationship is hidden in the changes of different temperature stages.
Correlation analysis showed that high temperature was correlated with distress, irritability, and hostility, but not with nervousness. This is because the correlation analysis is for linear correlation factors, while the Grey correlation analysis does not have this precondition. The Grey correlation analysis is applicable to linear and non-linear curves. Under low data requirements, the correlation between high temperature and the four elements of emotional health could be seen. Therefore, the correlation coefficient and the absolute correlation coefficient indicate that high temperature has a clear relationship with irritability, hostility, and distress. The composite correlation index indicates that high temperature has a stronger correlation with nervousness and irritability than with distress and hostility. Therefore, this paper decides to explore the relationship of high temperature with irritability, distress, hostility, and nervousness separately.
Relationship between high temperature and distress
There is a clear correlation between high temperature and distress. Using MATLAB’s regression analysis, it is found that a quadratic curve can be well-fitted between the two, and the regression equation is:
[Due to technical limitations, equation 1 only available in the manuscript file below.]
where R2 is 0.98, and RMSE is 0.015. The regression equation shows that (Figure 4) as the temperature rises, the effect of high temperature on distress changes in stages: at 35-38°C, the degree of influence rises rapidly; at 38-43°C, the degree of influence decreases gradually; at 43-46°C, this again increases gradually. The main reason for this is that at 35–38°C, the human body’s ability to regulate in high temperatures can initiate an emergency warning mechanism. At this time, the high temperature is not perceived as a threat and the degree of arousal is not high, so it is a phase with increasing distress [28]. At 38–43°C, the body temperature regulation mechanism enters the second-level early warning stage, the human body begins to protect itself and enters the resistance stage, the superficial veins dilate, the blood circulation is competent and perspiration is increased. The body’s energy is focused on coping with the external stimulation, thus bringing down the level of distress psychologically [29,30]. At 43–46°C, the temperature critically exceeds the effective adjustment range of the physiological warning system, and the individual consumes a large amount of energy in response to high temperature, the body fails to return to equilibrium and the individual once again perceives this high temperature as a threat and enters the exhaustion stage, thus presenting with the rising phase of distress [31].
Relationship between high temperature and irritability
There is a clear correlation between high temperature and irritability. Analysis shows that a cubic curve can be well-fitted between the two, and the regression equation is:
[Due to technical limitations, equation 2 only available in the manuscript file below.]
where R2 is 0.99, and RMSE is 0.003. The regression equation shows that (Figure 5) at 35–45°C, the effect of high temperature on irritability continues to rise with increasing temperature. The main reason is that as the temperature rises, the risk of high temperature to the body increases, and the intensity of arousal rises continuously. The investment in response to ambient high temperature gradually increases [30]. At this time, the human body will be in an “easily irritated state”. If one does not get one’s way, one would become angry. Some people will lose their emotional control.
Relationship between high temperature and hostility
There is a clear correlation between high temperature and hostility. Analysis shows that a quadratic curve can be well-fitted between the two, the regression equation being:
[Due to technical limitations, equation 3 only available in the manuscript file below.]
where R2 is 0.99, and RMSE is 0.001. The regression equation shows that (Figure 6) at 35–43°C, as the temperature increases, its effect on hostility rises rapidly;at 43–45°C, its effect on hostility slowly decreasing. The main reason is that at 35–43°C, as the temperature rises, the individual will concentrate more and more energy on the regulation against ambient temperature, so the hostility to the external environment’s interfering stimulation is gradually enhanced; when the temperature reaches 43°C, which exceeds the effective adjustment range of the physiological warning mechanism, the body can no longer return to equilibrium. At this time, an individual only wants to escape from this hot environment [32], which gradually decreases hostility.
Relationship between high temperature and nervousness
There is a clear correlation between high temperature and nervousness. Analysis shows that a cubic curve can be well-fitted between the two, with the regression equation being:
[Due to technical limitations, equation 4 only available in the manuscript file below.]
where R2 is 0.95, and RMSE is 0.005. The regression equation shows that (Figure 7), as the temperature increases, its effect on nervousness changes stage by stage. At 35–40°C, the degree of influence increases rapidly; at 40–44°C, the degree of influence is in a stationary stage; at 44–46°C, the degree of influence slowly rises. This is mainly because as the temperature increases, the level of emotional arousal rises, and its superposition with the unpleasant feeling brought by high temperature leads to emotional nervousness [28]. With the initiation of the body’s early warning mechanism for high temperature, individuals will focus on coping with environmental stimuli, and this nervousness enters a table stage.
Difference in the effects of high temperature on negative emotional elements
The effects of high temperature on different negative emotional elements were compared and it was found that the elements were affected by high temperature differently: distressed > irritable > nervous > hostile (Figure 8). The influence of high temperature is fluctuant on distress and hostility, is monotonically increasing on nervousness and irritability. The reason is that the impact of high ambient temperature on the human body is multi-layered and increases layer by layer. When the human body enters an environment with high temperature, the psychological response is often more sensitive than other responses, and in the scenario of slow adaptation, the human body responses to the high temperature emotionally through distressed and anxiety. When extreme or prolonged high temperatures cause negative physical and mental responses beyond the physiological and psychological tolerance of the human body, an individual will show impulsive irritability.
Combined effects of high temperature on negative emotions
The combined effect of high temperature on negative emotions is the comprehensive process of distress, irritability, nervousness, and hostility in individuals. Therefore, this paper will superimpose these four elements to analyze the composite effects of high temperature on emotional health. The results show that the regression equation for the combined effect of high temperature on negative emotions is:
[Due to technical limitations, equation 5 only available in the manuscript file below.]
where R2 is 0.97, and RMSE is 0.006. The regression equation shows (Figure 9) that
the effect of high temperature on emotional health appears to change in stages: Overall, the higher the ambient temperature, the worse the negative emotions. At 35-39 °C, with the increase in ambient temperature, degree of influence increases rapidly; at 39-43°C, the relationship between temperature and mood entered a stage of reverse changes, and the degree of influence decreases slightly with temperature. After 43°C, the negative emotion again rises but the rate is lower than at the 35-39°C stage. This indicates that individuals have different emotional characteristics in different temperature intervals in response to environmental stimuli.