Outdoor Cold Stress and Cold Risk for Children during Winter: A Study in China’s Severe Cold Regions

Abstract

This study uses the universal thermal climate index (UTCI) and whole-body and local cooling assessment to determine the thermal benchmarks and cold risk for children in China’s severe cold regions. The relevant measurements and survey were conducted in four open spaces at a children’s park in Harbin, China. The findings of the study are as follows: (1) In winter, solar radiation and global temperature affects winter thermal sensation in male and female children the most. (2) Female children have a lower neutral UTCI (6.0 °C) than male children (7.3 °C), and female children have lower upper and lower thresholds of the neutral UTCI range (−1.3–13.4 °C) than male children (0.6–14.1 °C). (3) Children who engaged in light-intensity activities, were exposed to cold winds, and touched cold surfaces with their bare fingers are at risk of whole-body and local cooling. (4) Children prefer exercising (P_Female = 35.5%, P_Male = 48.3%) and moving to sunshine for thermal adaptation (P_Female = 31.1%, P_Male = 26.4%). (5) Winter travel guidelines, cold-risk-prevention measures, and safety guidelines for winter outdoor activities are proposed. The results provide references for the design of open spaces in urban parks in China’s severe cold regions.

1. Introduction

Children are facing a series of new threats, such as rising sea levels, extreme weather events, high temperatures, and emerging infectious diseases [1]. Notably, childhood obesity is an immediate threat to children and a major public health challenge of the 21st century, with the number of obese children and adolescents increasing from 11 million in 1975 to 124 million in 2016 [2]. Obesity significantly affects a child’s physical health, social and emotional well-being, and self-esteem [3]. The relationship between low levels of physical or sedentary activities and the prevalence of obesity is well documented [4,5]. Physical activity in children is restricted by lack of exercise at school, increased internet usage, and parental concerns about injuries during activities [6]. Further, COVID-19 measures have adversely impacted the amount of physical activity that children experience [7]. In addition to obesity and reduced social life and outdoor activities, physical inactivity can also lead to inadequate calcium absorption, mental illness, decreased immunity, and other problems [8].

Physical activity is linked to improved cardiovascular risk factors and optimal bone and mental health in children [9,10]. Additionally, outdoor leisure activities, such as cycling and walking, directly affect physical and mental health [11]. The World Health Organization recommends that children and adolescents between ages 5 and 17 accumulate at least 60 min of moderate to vigorous-intensity physical activity every day [12]. Therefore, encouraging children to venture outdoors and participate in sports and social activities is of great significance to their healthy growth. In the urban environment, green spaces and sports activities are strongly correlated [13]. Even brief visits to natural spaces can have a positive impact on reducing people’s stress [14]. Children’s emotional and behavioral challenges share an inverse relationship with exposure to green spaces [15]. In addition, being in or near such spaces is associated with better test scores and cognitive abilities and greater self-discipline. It alleviates behavioral problems, such as attention-deficit and hyperactivity disorder, and prevents myopia [16]. Urban green spaces, including urban parks, provide an environment for socialization, and reduce feelings of isolation and loneliness [17,18].

In summary, guiding children from indoor to outdoor spaces and carrying out physical activities is beneficial to children’s health. However, environmental health risk assessments frequently find children to be more vulnerable [19]; this is because they spend more time outdoors than adults, increasing exposure to severe weather [20]. Therefore, it is crucial to explore the thermal comfort and safety of children in outdoor environments. Several researchers have studied the thermal comfort and safety of children in outdoor spaces. Some studies have reported differences in thermal perception and thermal comfort of children and adults. For example, Yun et al. [21] found that children felt warmer and preferred lower temperatures than adults. Teli et al. [22] found that school-going children were more sensitive to heat than adults. Nam et al. [23] evaluated the thermal comfort of preschool children aged 4–6 years in a kindergarten. The results showed that the mean values for summer and winter clothing were 0.29 clo and 0.81 clo, respectively. Both of them were less than that of the adult clothing provided by ASHRAE. The number of seasonal clothing differs between male and female children. In addition, the comfort temperature of children in winter and summer is lower than that of adults. It is another indicator that children’s thermal perception is different from that of adults. Cheng and Brown [24] modified the thermal comfort model COMFA into a child energy budget model by considering children’s heat exchange. The results indicated that the thermal acceptable range for children is different than that for adults. Contrarily, studies have focused on the effects of meteorological parameters, psychological factors, and socioeconomic background of children’s thermal comfort. Vanos et al. [25] explored children’s heat balance and outdoor thermal comfort, and demonstrated that radiation, air temperature, wind speed, and fatigue were important predictors of actual thermal sensation. Lam et al. [26] examined the relationship between short-term physiological and psychological thermal adaptation and outdoor thermal comfort of exercisers. They studied individuals in different climate zones in China, using first-year students as subjects. The results demonstrated differences in heart rate and thermal perception of native and non-native students. They highlighted that physiological and psychological factors, including mood and fatigue, are necessary to understand thermal perception in both acclimatized and non-adapted populations. Montazami et al. [27] investigated the relationship between children’s thermal perception at home, their adaptive behavior to achieve thermal comfort, and socioeconomic background. The results showed that the temperature perception ability of children from poor families between staying at home and school are strongly related. Children from disadvantaged backgrounds feel warmer in the classroom. In addition, studies have explored the thermal safety of children in outdoor environments. Mahé et al. [28] explored the risk of ultraviolet radiation-induced skin damage during outdoor sports and recommended that children take appropriate sun protection measures. Kennedy et al. [29] developed guidelines for thermal comfort on Canadian playgrounds. The results suggest that thermally safe and comfortable playgrounds minimize environmental health risks for children. Huang et al. [30] explored the thermal comfort and safety of children in the open space of urban parks in China’s cold region.

The thermal comfort and safety of children in outdoor environments are receiving attention. However, the risk of cold that children face in cold outdoor environments has been rarely studied. Studies have found that anthropogenic climate change may increase the risk of frostbite. Cold climatic conditions can have adverse effects on children’s health as their bodies are less efficient in preserving and producing heat [31]. Moreover, children have a larger surface-to-mass ratio, implying that they lose more body heat in cold environments [32,33]. In addition, children are not sufficiently attentive to personal cooling signals, such as pain and numbness [34]. Prolonged exposure to cold may lead to a drop in the body and core temperatures, which can be intensified by exposure to wind and contact with cold objects [35]. This is of particular concern in China’s severe cold regions, where children face discomfort and potential cold risks during outdoor activities. However, the main meteorological factors affecting the outdoor thermal comfort, heat benchmark, and thermal adaptation behavior of children in extremely cold regions are unclear. Hence, the cold risks they face in winter in these regions must be assessed.

Therefore, four representative open spaces in a children’s park in Harbin, China, were selected. The outdoor thermal comfort and whole-body and local cooling risks of children in winter were evaluated through meteorological measurements and questionnaires, in order to provide a theoretical reference for urban planners and landscape architects in severe cold regions to design more comfortable and safe outdoor open spaces for children.

Section 2 will introduce the methodology of this study, including key issues such as physical measurement and acquisition of subjective thermal perception and cold risk assessment methods. Section 3 presents the results of this study, including children’s heat benchmarks and exposure to cold risks. An in-depth analysis of the results, comparison with other similar studies, and strategies for cold risk prevention will be presented in Section 4. Conclusions will be drawn in Section 5.

2. Materials and Methods

2.1. Study Area

Field investigation and meteorological data collection were conducted in a children’s park in Harbin, Heilongjiang Province, China (126°38′58″ E, 45°45′30″ N). According to the Köppen climate classification, Harbin is located in the temperate monsoon climate zone (Dwa) [36]. In the construction of China’s climate boundary, Harbin is listed as a severe cold region [37,38]. Records from 1981 to 2010 reveal July as having the highest monthly average air temperature (T_a = 23.1 °C) and a maximum average temperature of 27.8 °C. Ta ranged from −22.9 °C to −12.0 °C. The lowest monthly average temperature occurred in January (−17.6 °C). The lowest average temperature occurred in January (−22.9 °C). The average relative humidity (RH) over the years fluctuated between 48% and 78% (Figure 1). As this study aimed to assess the outdoor thermal comfort and cold risk among children (hereinafter referred to as “subjects”) in severe cold regions in winter, meteorological measurements and questionnaires were conducted on the 12th, 13th, 14th, 17th, 18th, and 19th of January, the coldest month.

The temperature of the urban space is affected by the surrounding environment within a radius of 10–150 m [39]. Therefore, four open spaces were selected for measurement according to the density of children’s activities in winter. Fisheye photographs of the measurement sites were captured to determine the sky view factor (SVF) of each space (Figure 2).

2.2. Experimental Design

The field survey included meteorological data collection and synchronized questionnaires. The microclimate becomes more evident under clear and windless weather conditions, and is predominantly suppressed during a strong synoptic flow pattern, characterized by brisk winds, clouds, and occasional precipitation [40]. Therefore, the field investigations were performed on a sunny day without strong winds.

2.2.1. Meteorological Measurement and T_s

Winters in severe cold regions have shorter days and longer nights. Residents spend less time outdoors in winter than in summer and spring. Therefore, in this experiment, the time was set from 08:30 am to 15:30 pm in the winter of 2022. Meteorological parameters, T_a, RH, wind speed (V), solar radiation (G), and globe temperature (T_g) at four sites were recorded every minute during the experiment. T_a and RH were recorded by a HOBO onset U23-001 recorder (placed in a louvered box protected from solar radiation). V was recorded by Kestrel 5500 (Nielsen-Kellerman Co., Boothwyn, PA, USA). T_g was recorded by the black ball sensor of Delta HD 32.2 (Delta OHM, Caselle, Italy). TP3276.2 uses a black-ball thermometer to quantify the net effect of thermal radiation on the human body. G was recorded by a recorder (Pyranometer TBQ-2) that measured the solar radiation (

Table 1. Technical details of meteorological equipment.

Instrumentation	Parameter	Range	Accuracy	Picture
HOBO onset U23-001	Ta	−40–70 °C	±0.21 °C
	RH	0–100%	±2.5%
Kestrel 5500	V	0–40 m/s	0.1 m/s
Delta HD 32.2	Tg	−10–100 °C	±0.1 °C
Pyranometer TBQ-2	G	0–2000W/m2	≤±2%

). The instruments were mounted on a crossbar 1 m above the ground. The bar was fixed to a tripod to ensure that the instruments did not shade each other at any time (Figure 3). The mean radiant temperature (T_mrt) is defined as the uniform temperature of a hypothetical enclosure. In this enclosure, the radiative heat transfer from the human body is equal to the radiative heat transfer in an actual non-uniform enclosure [41]. The value of T_mrt can be determined using a black-ball thermometer. However, this method has limitations, since it can distinguish between neither the effects of short-wave and long-wave radiative flux densities, nor the radiative flux density in spatial directions [42]. However, it is a simple and inexpensive way to determine T_mrt [43]. The 0.05 m black-ball thermometer was chosen since it has a shorter response time compared to standard black-ball thermometers [44]. It ensures that the collected thermal perception corresponds in time to the meteorological data. T_mrt is calculated as follows:

$$T_{mrt} ={\left[{\left(T_g+273\right)}^4+\frac{1.10\times {10}^8{V}_a^{0.6}}{\epsilon D^{0.4}}\left(T_g-T_a\right)\right]}^{\frac{1}{4}}-273,$$

(1)

where D represents the diameter of the black sphere (0.05 m), and Ɛ the black sphere coefficient (0.95).

During the test, the surface temperature (T_s) of a child’s potential exposure to a cold object was measured and recorded every hour using an infrared thermal imaging camera (FLUKETiR110) (Figure 4). The temperature of the surface perpendicular to the direction of the sun’s radiation is taken as the T_s of the object according to the altitude angle of the sun when the photo was taken [30].

2.2.2. Survey Questionnaire

The United Nations Convention on the Rights of the Child defined subjects as persons under the age of 18 [45]. Children in the age group of 0–18 were chosen as the survey subjects. Consent was obtained from the subjects and their caregivers (if accompanied by caregivers) during the microclimate measurements. The subjects were given questionnaires to complete. Each questionnaire consisted of three parts, (1) the subjects’ personal statistics, (2) the subject’s thermal perception, including the thermal sensation, preference, comfort, and acceptability, and (3) the subject’s preferred response to cold and previous frostbite experience (Appendix A). The discrete-scale Likert scales were chosen instead of continuous scales to avoid further expansion of individual differences and reducing measurement uncertainty [46]. The first part of the questionnaire includes questions regarding the sex, age, height, weight, clothing of the subject, and type of activity performed by the subject in the past 20 min [21,30,47,48]. In the second part of the questionnaire, the thermal sensation was recorded on a nine-point scale (−4, very cold; −3, cold; −2, cool; −1, slightly cool; 0, neutral; 1, slightly warm; 2, warm; and 3, hot). Preferences for T_a, V, and G were recorded on a three-point scale (−1, higher/stronger; 0, no change; 1, lower/weaker). Thermal comfort was also expressed on a three-point scale (−1, discomfort; 0, moderate; 1, comfort). Finally, thermal acceptability was recorded on a two-point scale (−1, unacceptable; 1, acceptable).

The third part of the questionnaire directed respondents to choose their preferred winter heat adaptation behavior (drinking hot drinks, adding clothes, exercising, walking under the sun). Considering that subjects are generally unable to distinguish between or recall the sensations of numbness and pain, only the subjects’ cold injury experience (no frostbite, finger frostbite, toe frostbite, ear frostbite, and other frostbite) was investigated. The questionnaire was prepared and filled out in Chinese. Compared to adults, the subjects lacked the ability to recognize thermal sensations [21]. To help the subjects better understand the questionnaire and improve the accuracy of their responses, in situ interviews were conducted. Help was sought from their caregivers when necessary.

During the experiment, the number and type of activities in the four spaces were visually observed and captured on camera [49,50,51] from a vantage point (Appendix B). The procedure was repeated every 60 min (e.g., 09:00, 10:00, 11:00, etc.). The study only considered the active subjects (i.e., subjects sitting or playing) that were in each space for more than 10 min, excluding passersby or children who would temporarily stop at the park.

2.3. Metabolic Rate and Clothing Insulation

As the thermal insulation of children’s clothing is similar to that of adults in the same season [52], the thermal resistance value of children’s clothing according to ISO 9920 was evaluated [53]. Figure 5 illustrates the different clothing types for each part of the body and their thermal resistance values. It was assumed that subjects either choose to dress according to the outside temperature or a caregiver selected their clothing for them. The subjects’ activity types were recorded to determine their metabolic rates. In a relaxed sitting position, the average metabolic equivalent (MET) unit for adults is 58.2 W/m² [54], varies among subjects and, therefore, cannot be directly applied. Instead, an average resting metabolic rate (RMR) of 48.8 W/m² for subjects (7–11 y) was used [21,30,47,48].

Table 2. Activity types, codes, MET, and modified metabolic value among physical activities intensity levels.

Physical Activities Levels	Activities	Activity Coding	Met Units	Metabolic Rate Corrections (W/m2)
Light intensity	Sitting	07021	1.3	63.4
<3 Met	Standing	09050	1.8	87.8
	Walking, very slow	17151	2.0	97.6
	Dog sledding, passenger	19006	2.5	122.0
Moderate intensity	Table tennis	15660	4.0	195.2
3–6 Met	Skating, ice, 4 m/s or less	19020	5.5	268.4
	Children’s games	15135	5.8	283.0
Vigorous intensity	Running	12029	6.0	292.8
>6 Met	Skating	19030	7.0	341.6

lists the metabolic rate corrections in subjects for different activities at light, moderate, and vigorous intensities [55].

2.4. Thermal Indices

The Universal Thermal Climate Index (UTCI) was used to assess thermal comfort in children. It simulates the effects of thermoregulation and clothing on activities in outdoor environments based on the multi-node human physiology of the Fiala model. As a human-body thermoregulation system model, it considers the spatial asymmetry of the environment and the exposure of individual body parts in the simulation of radiative heat exchange between humans and their surroundings. Respiration is simulated by considering convection and latent heat losses. The model also includes shortwave radiation to analyze the effects of solar radiation and other sources of high temperature on the human body. It can be applied to all weathers, seasons, and spatial scales [56]. The meteorological parameters T_a, RH, V, G, T_mrt, and others, and the basic attributes of the subjects, i.e., height, weight, age, sex, clothing thermal resistance, and metabolic rate, were input to the RayMan model. The UTCI was calculated in steps of 0.5 h [30,57,58,59,60,61].

2.5. Cold Risk Assessment

2.5.1. Whole-Body Cooling Assessment

The required basic clothing insulation (ICL) is the basic clothing insulation value required to maintain the human body in thermal equilibrium with the acceptable body temperature and skin temperature levels under ambient conditions. Calculating the ICL will reveal if the thermal resistance of the selected garment can bring the person to thermal equilibrium and help assess whole-body cooling. The ICL was calculated by the IREQ model (ISO 11079:2007, http://wwwold.eat.lth.se/Research/Thermal/TEL118ToolEn.htm, accessed on 10 April 2022) [62,63]. The meteorological data T_a, RH, V, and T_mrt, and the metabolic values obtained from field measurements were input to the program. The results were compared with the clothing thermal resistance (I_cl) collected in this study.

2.5.2. Local Cooling Assessment

(1)

Determination of wind cooling

Wind has a cooling effect on exposed skin, which can be expressed as the chill temperature (t_WC) [64].

t_WC = 13.12 + 0.6215·T_a − 11.37·V₁₀^0.16 + 0.3965·T_aV₁₀^0.16

(2)

Since the V was measured at ground level, V was calculated at 10 m (V₁₀) by multiplying V by 1.5 in (2). The average t_WC was calculated in each space from 08:30 am to 3:30 pm at 1-h intervals to evaluate the cold risk brought by wind to the subjects in different spaces and time periods.

(2)

Contact of bare skin with cold surfaces

Exposure of bare skin to icy surfaces lowers its temperature, potentially causing pain, numbness, and frostbite. Finger touching and hand gripping correspond to different cold risk thresholds [65]. The T_s of different materials with the corresponding cold risk thresholds were compared to assess the risk of cold injury to children.

3. Results

3.1. Descriptive Analysis

3.1.1. Volunteers’ Attributes

Six hundred and thirty questionnaires were distributed, and 607 valid questionnaires were recovered. The sex distribution of the respondents was 58.7% male and 41.3% female.

Table 3. Characteristics of survey respondents.

		Male	Female	All
Number		333	274	607
Age (years)	Min	3	3	3
	Max	16	18	18
	Mean ± SD	9.7 ± 2.6	8.9 ± 2.6	9.4 ± 2.7
Height (cm)	Min	90	80	80
	Max	185	170	185
	Mean ± SD	143.3 ± 16.6	137.5 ± 15.9	140.7 ± 16.5
Weight (kg)	Min	15	11	11
	Max	90	80	90
	Mean ± SD	39.0 ± 13.5	32.5 ± 10.9	36.1 ± 12.8
Icl (clo)	Min	1.09	1.17	1.09
	Max	2.82	2.71	2.82
	Mean ± SD	1.87 ± 0.25	1.98 ± 0.23	1.92 ± 0.25
Metabolic rate (W/m2 )	Min	48.8	48.8	48.8
	Max	292.8	268.4	292.8
	Mean ± SD	134.8 ± 49.8	153.7 ± 55.9	143.3 ± 53.4

displays the physical attributes of the respondents (i.e., age, height, and weight). The thermal resistance of clothing is expressed in clo. The thermal resistance value of male clothing in winter was 1.87 ± 0.25 clo. That of female clothing was 1.98 ± 0.23 clo. According to the adjusted metabolic rate, the mean metabolic rates of males and females during the trial period were 134.8 ± 49.8 and 153.7 ± 55.9 W/m², respectively. All respondents had lived in Harbin for more than 1 year and were acclimated to the local weather. They can accurately and objectively evaluate the outdoor thermal environment either by themselves or with the help of their caregivers.

3.1.2. Meteorological Parameters

In winter, the differences in T_a and RH across the four spaces were small. The average T_a was approximately −17 °C. Furthermore, the average V of the OS was the highest, reaching 1.2 m/s. This is because the SVF of the OS was large and the space was not blocked by any structures or plants, which was conducive to the passage of wind. The average V of space SP was the lowest at 0.8 m/s. This is because the space was surrounded by slides and plants. In addition, the differences in G, T_g, and T_mrt were large. Among these, the average G of the OS was the largest, which was 207.4 W/m². The average G of the SP was the smallest at 146.5 W/m² This is because evergreen conifers and cypresses were planted on the southern side of this space. The average T_g values for the OS (−12.2 °C) and SR (−11.7 °C) were larger than those for the SP (−12.5 °C) and SS (−13.2 °C). This is likely because the SVFs of the OS and SR were larger. A higher G leads to an increase in the radiation temperature. The average T_mrt of the OS was the largest at 10.1 °C, whereas the T_mrt of the SP and SS was only 2 °C and 2.1 °C, respectively (

Table 4. Measurements of meteorological variables among sites.

		SP	OS	SS	SR
Ta (°C)	Min	−22.5	−22.6	−20.9	−21.2
	Max	−11.3	−11.8	−12.4	−12.5
	Mean ± SD	−16.8 ± 3.2	−16.9 ± 3.1	−16.8 ± 1.6	−16.7 ± 1.7
RH (%)	Min	13.4	18.2	8.6	13.9
	Max	66.4	66.2	63.1	63.3
	Mean ± SD	54.2 ± 7.7	54.8 ± 6.5	55.6 ± 7.1	53.9 ± 7.4
V(m/s)	Min	0	0	0	0
	Max	3.4	4.4	4	4.4
	Mean ± SD	0.8 ± 0.6	1.2 ± 0.7	0.9 ± 0.6	0.9 ± 0.8
G (W/m2)	Min	17	26	31	35
	Max	344	449	415	468
	Mean ± SD	146.5 ± 102.7	207.4 ± 116	155.3 ± 97.6	186.6 ± 127.7
Tg (°C)	Min	−22.2	−22.3	−20.9	−21.1
	Max	1.2	−3.4	−7.7	−1.3
	Mean ± SD	−12.5 ± 5.5	−12.2 ± 4.7	−13.2 ± 3.1	−11.7 ± 5.2
Tmrt (°C)	Min	−29.6	−27.4	−35.2	−43.9
	Max	60.7	59.9	46.5	66.9
	Mean ± SD	2 ± 19.5	10.1 ± 18.2	2.1 ± 14.4	4.6 ± 22.3

).

3.1.3. Meteorological Variables and TSV

T_a, RH, V, and T_g are considered key factors affecting the OTC of public open spaces [66]. To quantify the relative contributions of these meteorological variables to thermal sensation, Spearman correlation analyses and the thermal sensation vote (TSV) in winter for males, females, and the population were performed. The meteorological parameters affecting the children’s thermal perception in winter were G, T_g, and T_mrt. Among them, G was the most important factor affecting the male TSV (ρ = 0.272). T_g was the most important factor affecting the female TSV (ρ = 0.149). The second most influential factor affecting the TSV of both male and female subjects was T_mrt (ρ_male = 0.238, ρ_female = 0.238). However, the effects of T_a, RH, and V on the TSV of subjects in winter were unclear (

Table 5. Spearman correlation statistics of TSV and meteorological parameters.

	Gender	Ta	RH	V	G	Tg	Tmrt
TSV	Male	0.020	0.081	0.083	0.272 **	0.201 **	0.238 **
	Female	0.081	−0.011	−0.027	0.123 *	0.149 *	0.138 *
	All	0.053	0.044	0.030	0.200 **	0.178 **	0.190 **

** Significant at the 0.01 level. * Significant at the 0.05 level.

).

3.1.4. Preference Vote

In winter, 62.0% of female subjects and 55.6% of male subjects wanted T_a “higher”. Of the study population, 33.6% of female subjects and 37.5% of male subjects chose no change. There were only 4.4% of female subjects and 6.9% of male subjects who wanted T_a “lower”. The proportions of female and male subjects’ V preference votes were 45.3% and 38.4% for “lower”, 51.1% and 55.9% for “no change”, and 3.6% and 5.7% for “higher”, respectively. The proportions of female and male subjects’ G preference votes were 58.4% and 64% for “stronger”, 35.8% and 31.5% for “no change”, and only 5.8% and 4.5% for “weaker”, respectively (Figure 6).

3.1.5. Thermal Comfort Vote (TCV)

In winter, the difference in thermal comfort votes between the two sexes was small, with approximately half of them voting “comfortable” (49.8%), less than half “neutral” (45.5%), and a few “uncomfortable” (4.8%) (Figure 7). The winter outdoor temperature in China’s severe cold regions is approximately −17.6 °C. However, most subjects voted “neutral” or “comfortable.” It may be because they are physiologically acclimated to these temperatures and possess reasonable thermal adaptation to resist the cold.

3.2. Thermal Benchmarks

3.2.1. Neutral UTCI (NUTCI) and Neutral UTCI Range (NUTCIR)

The weighted mean TSV (MTSV) was calculated per 1 °C UTCI interval for children (female, male, and overall) in the winter. The slopes of the regression curve for the female and male subjects were 0.0682 and 0.0742, corresponding to the UTCI/MTSV of 14.7 °C and 13.5 °C, respectively (Figure 8a). This suggests that female subjects were slightly less sensitive to heat than the male subjects under frigid conditions. Combined with the graphs, under the same UTCI in winter, the female subjects had a higher MTSV than the male subjects. Hence, the female subjects (153.7 W/m²) had higher active metabolic levels than the male subjects (134.8 W/m²). Additionally, the female subjects wore more clothing (1.98 > 1.87 clo), making them more tolerant to extreme cold. This finding is consistent with the results of previous studies [21]. The slope of the regression curve for the population of all respondents was 0.0686, corresponding to a UTCI/MTSV of 14.6 °C (Figure 8b).

The neutral temperature is the degree of temperature at which people feel neither hot nor cold [67]. When MTSV = 0, the NUTCIs for female and male subjects in winter were 6.0 and 7.3 °C, respectively. The NUTCI for the overall respondents was 6.7 °C. NUTCIR is the temperature range corresponding to a TSV between −0.5 and 0.5. Thus, winter NUTCIR was −1.3–13.4 °C for female subjects, 0.6–14.1 °C for male subjects, and 0.5–14.0 °C for all the respondents. Compared to the male subjects, the female subjects had 1.3 °C lower NUTCI, 1.9 °C lower NUTCIR lower limit, and 0.6 °C lower upper limit. This may be because the female subjects have higher average clothing thermal resistance and average activity metabolism in winters in severe cold regions than the male subjects.

MTSV_Female = 0.0682UTCI 0.4113 (R² = 0.6897, p < 0.001)

(3)

MTSV_Male = 0.0742UTCI 0.5429 (R² = 0.7129, p < 0.001)

(4)

MTSV_all = 0.0686UTCI 0.4626 (R² = 0.8043, p < 0.001)

(5)

3.2.2. Thermal Acceptability Range (TAR)

A thermal condition is considered acceptable if at least 80% of the respondents find it acceptable [67]. This study constructed a quadratic polynomial fit curve to calculate the percentage of respondents who voted “unacceptable” for each 1 °C UTCI interval. The “unacceptable” points of the five grades on the cold end of the scale were 35%, 50%, 65%, 80%, and >80%, respectively (Table 3). The “mild heat stress” category is not displayed, as there is no physiological response to mild heat stress in the simulation. Therefore, the UTCI does not possess this category [68]. Figure 9 reveals that the overall minimum “thermally unacceptable” ratio of female to male subjects is greater than 20%, i.e., the maximum is less than 80%, indicating that the outdoor environment in severe cold regions does not have comfortable thermal conditions for subjects in winter. The lower limit of the UTCI range corresponding to each grade of cold stress in the female subjects was lower than that in males. It further indicates that the female subjects are more tolerant of cold than the male subjects.

3.3. Thermal Comfort Calendar and Space Attendance

3.3.1. Thermal Comfort Calendar

Thermal benchmarks and calendars objectively and accurately define thermal conditions in children’s activity spaces [69,70]. A thermal comfort calendar was proposed to help subjects choose the most appropriate time and space for physical activities. In addition, thermal conditions in each space were divided into 1-h intervals. Each color on the calendar represented a UTCI range of approximately 2 °C. The modified UTCI range corresponding to different thermal sensations was used to describe the thermal conditions of subjects in various spaces (

Table 6. UTCI calibrations for different stress categories.

Thermal Sensation	UTCI (°C)	Modified UTCI (°C) (Female)	Modified UTCI (°C) (Male)	Modified UTCI (°C) (All)
Extreme cold stress	<−40	<−20.8	<−19.8	<−20.5
Very strong cold stress	−40 to −27	−20.8 to −17.5	−19.8 to −16.6	−20.5 to −17.1
Strong cold stress	−27 to −13	−17.5 to −13.4	−16.6 to −12.5	−17.1 to −12.8
Moderate cold stress	−13 to 0	−13.4 to −6.6	−12.5 to −5.6	−12.8 to −6.2
Slight cold stress	0 to 9	−6.6 to 3.5	−5.6 to 2.8	−6.2 to 7.0
No thermal stress	9 to 26	-	-	-

).

In winter, cold stress exists in every space. The OS and SR exhibited a minor cold stress between 10:30 a.m. and 12:30 p.m. since they do not contain buildings and plants. The solar radiation in the spaces gradually increased. After 12:30, the intensity of solar radiation weakened, and the cold stress increased, resulting in a moderate to strong cold stress. Unlike the OS and SR, the SS contains deciduous trees and children’s slides. The tree trunks and facilities provide partial shade. Meanwhile, the children’s slides obstructed the wind from the northwest side and reduced the wind speed. These factors increased the cold stress of people in the spaces. The thermal condition between strong and moderate cold stress was relatively stable. The SP had the strongest cold stress, with extreme cold stress and strong cold stress in the morning, moderate cold stress as the day progressed, and strong cold stress again at 14:30 pm (Figure 10).

3.3.2. Space Attendance

To understand the impact of outdoor thermal environment on children’s activities, the number of subjects and types of activity they performed in each space were recorded every 60 min and the corresponding spatiotemporal distribution map was plotted (Figure 11). During the winter, subjects performed the activities with different frequencies. The OS and SR, which correspond to the two spaces with a larger SVF, a stronger G, and a higher T_a, were more popular among the children. The children performed the least number of activities in the SP, presumably due to the presence of conifers and cypress evergreens on the south side of the SP space that resulted in a lower G (146.5 W/m²) and T_g (−12.5 °C) in that area.

In addition, subjects infrequently chose light-intensity activities across the spaces, with moderate-intensity activities having the highest frequency. It was probably because the subjects relied on higher-intensity activities to keep warm during cold winters. Vigorous activities had the lowest frequency because subjects wore more clothing, which was not conducive to their vigorous-intensity activities. In general, from 09:00 a.m. to 11:00 a.m., as G and Ta increased, the number of subjects participating in outdoor activities gradually increased. The number of activities reduced from 11:00 a.m. to 12:00 p.m., since this period is considered lunchtime in Harbin. Subsequently, the frequency of activities resurged until 14:00 p.m., when the number of subjects in all spaces peaked. Subsequently, as G and Ta decreased, children began to leave the spaces, i.e., fewer subjects were present.

3.4. Cold Risk Assessment

3.4.1. Frostbite Experience

More than 31.1% of the subjects experienced frostbite in different body parts, while 68.9% did not. The cold risk faced by the subjects in severe cold regions in winter should receive more attention. Among them, 14.8% of the subjects had suffered frostbite on their fingers, possibly because the children’s fingers were exposed to cold weather for a long time or came in contact with cold surfaces. Approximately 16.6% of frostbitten ears may be because the subjects did not wear protective gear for their ears, such as earmuffs or hats with earmuffs. Approximately 2.5% of the subjects had frostbitten toes because they were playing outdoors while wearing shoes with thin soles and were in prolonged contact with the icy ground (Figure 12).

3.4.2. Whole-Body Cooling Assessment

Table 7. IREQ, ICL, and DLE corresponding to light-, moderate-, and vigorous-intensity activities.

PAs Levels	Icl	IREQmin	IREQneutral	ICLmin	ICLneutral	DLEmin	DLEneutral
Light	1.88	3.2	3.5	3.5	3.9	0.7	0.6
Moderate	1.95	1.5	1.8	1.7	2.0	>8	>8
Vigorous	1.44	0.6	0.9	0.7	1.0	>8	>8
ALL	1.90	1.9	2.2	2.1	2.5	3.2	1.3

lists the required clothing insulation (IREQ), ICL, and duration limited exposure (DLE) for subjects performing light to vigorous activities, where ICL_neutral is the basic clothing insulation value required by a human body to maintain the state of thermal equilibrium in a real environment. Subjects at different levels of activity are prone to different degrees of whole-body cooling. Subjects playing low-intensity games had a smaller average I_cl than that required for the body to reach thermal equilibrium (1.88 < 3.9 clo). Therefore, subjects at this activity level were wearing thinner clothing.

Spending a maximum of 42 min (0.7 h) outdoors (DLE_min = 0.7) increased the subjects’ risk of hypothermia with gradual exposure. The average clothing thermal resistance of the subjects performing moderate activity levels was between ICL_min and ICL_neutral (1.7 < 1.95 < 2.0 clo). It indicates that their clothing provided adequate insulation. Thermal conditions were considered “slightly cold” to “neutral”. Next, the local cooling effect was evaluated. The average clothing thermal resistance of the vigorous-intensity-activity group was greater than ICL_neutral (1.44 > 1.0 clo). It indicated that their clothing provided excess insulation. Overall, the subjects’ average clothing thermal resistance in winter was smaller than ICL_min. Assuming the body’s thermal balance is maintained, it is recommended that children exercise outdoors for 1.3 to 3.2 h.

3.4.3. Local Cooling Assessment

(1)

Assessment of wind cooling

Cold winds can cause frostbite, which can be classified into four levels [Appendix C (ISO15743, 2008)]. As indicated in the chart, t_WC maintains an upward trend during the test period, albeit always less than −10 °C. The t_WC of the SP, SS, and SR were always greater than −24 °C, i.e., Level 1 cooling risk. Thus, the skin is uncomfortably cold. In particular, the change of t_WC in the OS was the most significant. With a t_WC < −24 °C before 10:00, subjects were exposed to Level 2, i.e., skin frostbite. As the solar radiation increased and the space temperature increased, t_WC also gradually increased. However, the risk was still Level 1 (Figure 13).

(2)

Assessment for contact with cold surfaces

The cold risk depends on the contact method, type of contact material, and T_s of the material. Threshold intervals for other materials can be estimated based on the thermal properties of the materials [65]. In this study, the time taken by a subject to slowly recover from falling to the cold ground (10 s) was assumed to be the general time for a finger to touch a cold surface.

Table 8. Summary of the average T_s of various materials in each space in winter.

	Materials	Thermal Conductivity	In the Shade (°C)			In the Sun (°C)
		W/(m·K)	max	ave	min	max	ave	min
Brick	Brick	0.63	−15.9	−21.3 ± 3.1	−27.2	−12.6	−17.7 ± 2.5	−24.4
Stone brick	Stone	0.92	−17.1	−22.5 ± 2.6	−25.9	−14.1	−21.1 ± 2.9	−28.2
Ice	Ice (−15 °C)	2.4 [71]				−13.4	−18.3 ± 3.6	−25.3
Chair	Wood	0.18	−17.9	−20.2 ± 1.0	−22	−7.4	−11.4 ± 1.3	−16.8
Plastic slide	Polyamides	0.21	−16.4	−20.3 ± 2.1	−25.1	−10.7	−15.7 ± 3.6	−21.8
Slide handrail	Steel	45.3	−16.2	−19.5 ± 1.8	−23.1	−14.3	−17.8 ± 2.5	−21.7

lists the thermal conductivity of different materials and field measurements of T_s. The thermal conductivity of the materials in descending order is steel > ice > stone > brick > polyamides (nylon) > wood. The corresponding cold risk threshold in the descending order is steel > ice > stone > brick > polyamides (nylon) > wood.

Table 9. Cold risk thresholds for hand contact with different materials [65].

	Contact Period	Cold Risk	Aluminium	Steel	Stone	Nylon	Wood
Finger touching	10 s	Pain	>5	>5	4	−6	−10
		Numbness	3	−1	−15	−40	≤−40
		Frostbite	−7	−13	−18	-	-
Hand gripping	100 s	Pain	−4	−7	−17	−33	≤−40

lists the cold risk thresholds for exposure to common materials. The average surface temperature of wooden seats under sunlight (−11.4 °C) was 1.4 °C lower than the pain threshold (−10 °C) of fingers, resulting in the potential risk of finger pain when touching the wooden seats, plastic slides, and permeable bricks. The average temperature of the stone brick surface under sunlight (−21.1 °C) was 6.1 °C lower than the threshold for numbness (−15 °C), and 3.1 °C lower than the threshold for freezing (−18 °C). Skin contact with stone bricks, ice, and slide rails could cause numbness and frostbite. Subjects exposed to shaded materials were at greater risk of frostbites.

Subjects faced a lower risk by gripping objects with their hands rather than by touching them with their fingers [65]. When the subjects were playing on the slide, the maximum temperature of the iron handrail (−16.2 °C) was lower than the pain threshold (−7 °C) for 100 s of contact. Although the children did not constantly touch the handrail, they should still be aware of the risk during play.

3.5. Thermal Adaptation Behaviors

Figure 14 depicts children’s thermal adaptation behavior in winter. Female subjects chose exercise (35.5%) and moving to sunshine (31.1%) as their preferred thermal adaptation behaviors. Compared to the female subjects, more male subjects preferred exercise (48.3%) and moving to sunshine (26.4%) to relieve discomfort from the cold. This implies that children in China’s severe cold regions tend to cope with the cold winter environment by increasing metabolic heat production through exercising and exposure to solar radiation. Few preferred adding clothing and drinking hot water to relieve cold discomfort. Among them, 19% and 12.9% of female and male subjects preferred drinking hot fluids, respectively, while 14.3% and 12.3% of female and male subjects preferred adding clothes to relieve cold discomfort, respectively. In severe cold regions in winter, female and male children wear heavy clothes. Hence, their thermal resistances reach 1.98 clo and 1.87 clo, respectively. In a harsh thermal environment, the blood vessels of the extremities begin to constrict, and little heat can enter the extremities. This means that the increase in the thermal resistance of the clothing does not stop the extremities from cooling down further. Thus, the only method to reheat the extremities in time to prevent damage from the cold is by increasing the metabolic rate or providing external heat. Moreover, excess clothing hampers mobility [72].

4. Discussion

4.1. Thermal Benchmarks

4.1.1. NUTCI

This study calculated a lower NUTCI (6.7 °C) than a similar mixed-age study (19.3 °C) conducted in Harbin, China. The likely cause of this is the different study season and subject age group. Compared to the NUTCI of studies of the same age group, the NUTCI (6.7 °C) of subjects in Harbin was 5.5 °C lower than that in Xi’an (12.2 °C) [30]. This was because Xi’an is a cold region, while Harbin is a severe cold region. Harbin has a lower average temperature in January than Xi’an (−17.6 < 0.6 °C). Moreover, omitting the age difference, children in Harbin have a smaller NUTCI in winter (6.7 < 12 °C) than young adults in Xi’an. This is because of the different climates, clothing habits, and metabolisms. Children (143.3 W/m²) in Harbin had faster metabolisms than young adults (115 W/m²). Further, having lived in severe cold areas for a longer time, the subjects were psychologically prepared for low temperatures. The subjects have a 10.8 °C smaller NUTCI than the people of Tianjin because of differences in body composition, climate of the study area, and study season. The study in Tianjin investigated the year-round outdoor thermal comfort of children, adults, and the elderly, whereas this study focused on the outdoor thermal comfort of children in the severe cold regions of China in winter. Harbin has cold and long winters and short and hot summers, similar to Umeå, Sweden [36]. The NUTCI of subjects was 7.7 °C lower than that of Umeå, Sweden, which may be caused by the different seasons of the survey. The above analysis shows that different age ranges in the same climate zone, the same age range in different climate zones, and different study seasons have different NUTCI values, which proves that long-term thermal adaptation has an important impact on the thermal comfort of local residents (

Table 10. Neutral UTCI in different OTC studies.

City, Country	Climate Zone	Seasons	Population	NUTCI (°C)	Analysis Methods
Harbin, China (this study)	Dwa	Winter	Children	6.7	LR, MTSV vs. UTCI bin (1 °C)
Xi’an, China [30]	Cwa/BSk	Winter	Children	12.2	LR, MTSV vs. UTCI bin (1 °C)
Harbin, China [73]	Dwa	Summer	Mixed ages	19.3	LR, MTSV vs. UTCI bin (1 °C)
Xi’an, China [58]	BSk/Cwa	Winter	Young adult	12.0	LR, MTSV vs. UTCI bin (1 °C)
Tianjin, China [74]	Dwa/BSk	All	Mixed ages	17.5	LR, MTSV vs. UTCI bin (1 °C)
Umeå, Sweden [75]	Dfc	Summer	Mixed ages	14.4	LR, MTSV vs. UTCI bin (1 °C)

LR represents linear regression.

).

4.1.2. NUTCIR

Comparing the subjects’ NUTCIR in Harbin with those of the other five studies reveals distinct differences. Subjects in Harbin had lower upper and lower NUTCIR limits (

Table 11. Neutral UTCI range in different OTC studies.

City, Country	Climate Zone	Seasons	Population	NUTCIR (°C)	Analysis Methods
Harbin, China (This study)	Dwa	Winter	Children	0.6–14.1	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5
Xi’an, China [30]	BSk/Cwa	Winter	Children	7.7–16.6	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5
Harbin, China [73]	Dwa	Summer	Mixed ages	15.6–23.0	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5
Xi’an, China [58]	BSk/Cwa	Winter	Young adult	9.1–14.9	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5
Tianjin, China [74]	Dwa/BSk	All	Mixed ages	13.6–21.3	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5
Umeå, Sweden [75]	Dfc	Summer	Mixed ages	11.5–17.2	LR, MTSV vs. UTCI bin (1 °C), TSV = ±0.5

LR represents Linear Regression.

). Second, subjects in Harbin also had lower NUTCIR limits (0.6–14.1 °C) than those in Xi’an (7.7–16.6 °C). This because Harbin is a severe cold region, where the winter temperature is lower and children are more tolerant of the cold. Compared to Zhu, Liang, Sun, and Han [73], although the study sites were all in Harbin, the subjects and seasons were different and subjects in this study had a lower NUTCIR. This trend has two reasons: children have a warmer thermal sensation than adults, and, therefore, prefer lower temperatures [21] and the seasonal differences. Compared with the NUTCIR of young adults in Xi’an, the NUTCIR of children in Harbin has a lower threshold and a wider range due to the climatic differences of the study areas. The subjects in the Xi’an study preferred to stand or sit, whereas those in this study chose to skate, play outdoor games, and do other physical activities. Further, the subjects of this study had a faster metabolism.

Harbin’s NUTCIR is wider because there are larger climate fluctuations year-round. The locals (children) of Harbin, who are acclimated to such climatic conditions, are more tolerant to the weather. The higher NUTCIR in Tianjin is caused by the difference in study seasons and subjects. Umeå and Harbin also have markedly different NUTCIRs. Umeå’s NUTCIR is narrower, and its upper limit is 3.1 °C higher than that of Harbin’s. The two cities have similar climates, with cold and long winters and short and hot summers. However, Harbin’s children have a wider NUTCIR in winter, and Umeå’s subjects have a narrower NUTCIR in summer. This analysis demonstrates that people living in different climate zones, or in the same climate zone but different age groups and survey seasons, have different NUTCIRs. This proves that long-term thermal adaptation has a remarkable impact on the thermal comfort of local residents.

4.2. Attendance Patterns

Our study revealed that the meteorological parameters affecting the thermal sensation votes of children in severe cold regions were G, T_g, and T_mrt. The attendance rate of subjects in winter was affected by the spatial microclimate. With the increase in T_g and G, the number of attendees increased, until noon, when the number of people decreased. This trend is observed because noon is the lunchtime in Harbin, after which the number of attendees peaked. In the afternoon, as T_g and G decreased, the number of attendees dwindled. This is consistent with previous research [30]. Studies analyzing survey attendance in mixed populations found similar results [49,76,77]. In this study, the microclimate of the park space was the worst among the four spaces with the lowest G (146.5 W/m²) and second lowest T_g (−12.5 °C). However, many subjects missed the survey. The SS has two children’s slides. The taller slide restricts the G in the space, lowering the T_g. The OS and SR are not enclosed, with a relatively strong G and higher T_g than the other spaces. Hence, they received a higher attendance rate. The children’s preferred winter outdoor activities in the severe cold region had strong regional characteristics. More subjects engaged in ice and snow activities, such as skating and sledding. Therefore, the functional attributes of the space also affected the children’s attendance. Based on the assessment of cold stress, it is recommended that children engage themselves in physical activities at the park between 10:30 am and 2:30 pm. They used the OS and SR as these spaces have a larger SVF and more solar radiation.

Xu, Hong, Jiang, An, and Zhang [59] plotted a thermal comfort calendar in the shade for winter and summer in a Xi’an park, which showed that “strong cold stress” or stronger occurred after 16:00. Huang, Hong, Tian, Yuan, and Su [30] also plotted a thermal comfort calendar for winter and summer in a Xi’an park, in which “slight cold stress” was strongest in winter between 9:30 and 17:30 on the survey day. The results demonstrate that “strong cold stress” in the park open space occurred after 14:30, and “very strong cold stress” occurred before 9:30 am. This suggests that outdoor cold stress in severe cold regions has greater intensity and lasts longer.

4.3. Thermal Environment Safety

4.3.1. Thermal Environment Risk

The process of urbanization has been accelerated with the continuous development of the global economy and society, and urbanization and climate change have increasingly become international issues [78]. In the context of climate change, although the climate continues to warm, colder climatic conditions have more adverse health effects, and children are particularly vulnerable owing to a lower ability to preserve or generate body temperature [31]. The researchers measured the T_s of different landscape materials in cold region parks to assess thermal risk in children. The results demonstrated that the high T_s of permeable bricks, asphalt, wooden seats, and wooden floors under sunlight in summer would likely endanger the thermal safety of children [30]. Different from the existing thermal environmental risk in cold regions, the predominant outdoor thermal environmental risk in severe cold regions is cold injury. Low wind speeds with temperatures below −15 °C are common in extremely cold regions during winter. Such an environment can cause frostbite [79]. However, frostbite also occurs when skin comes into contact with cold surfaces (e.g., metals, equipment, liquids) [80]. Exposure to cold surfaces decreases skin temperature, which contributes toward varying degrees of cold risk. Pain, numbness, and frostbite occur when the skin temperature drops to 15, 7, and 0 °C [81]. Children have a larger surface-to-mass ratio and lose more body heat than adults [82], therefore, they are more susceptible to cold injury in such environments [79]. Section 3.3.2 indicates that children play on hard surfaces, ice rinks, and other facilities during winter. Thus, they are at risk of both whole-body and local cooling.

4.3.2. Cold Risk Prevention

Table 12. Cold risk analysis and corresponding prevention strategies.

Cold Risk Analysis	Prevention Strategies
Children with light-intensity activities had Icl less than ICLmin (1.88 clo < 3.9 clo), DLEmin = 0.7 h. The risk of hypothermia increased with gradual exposure.	Increase activity intensity to increase metabolic heat production. Wear warmer clothes. Control the length of outdoor activities and enter shelter in time to restore body temperature.
The Icl of children with vigorous-intensity activities was greater than ICLneutral (1.44 clo > 1.0 clo), which caused sweating and accelerated the cooling rate of the body.	Reduce the activity intensity and change into dry clothes in time to avoid accelerating body cooling after the clothes are soaked in water. Control the length of outdoor activities and enter shelter in time to restore body temperature.
Overall, the children’s Icl was less than ICLmin, DLEmin = 3.2 h.	Wear loose-fitting clothing with higher thermal resistance. Avoid sweating due to excessive activity. Control activity time and avoid prolonged exposure to the cold environment.
With tWC less than −24 °C before 10:00 in space OS, children were exposed to Level 2 cooling risk with the risk of skin frostbite.	Adjust travel time and location. Choose a more suitable space and location for the event. Wear warm clothes. Wear gloves, masks, scarves, and hats with earmuffs to avoid frostbite from exposure to cold winds.
The tWC of space SP, SS, SR was always greater than −24 °C and less than −10 °C; so, it was always at the risk of Level 1 cooling, and the skin was exposed to uncomfortable cold.	Wear warm clothes. Wear masks, scarves, and hats with earmuffs, etc., to avoid exposing your skin to cold winds. Control the length of outdoor activities and avoid prolonged exposure to cold wind.
The average surface temperature of wooden seats in sunlight (−11.4 °C) was 1.4 °C lower than the pain threshold (−10 °C) for fingers touching wood surfaces. Touching wooden seats and plastic slides might cause pain.	Use caution with cold surfaces. Minimize exposure to cold surfaces without gloves. Wear gloves.
The average temperature of the stone brick surface under sunlight (−21.1 °C) was 6.1 °C lower than the numbness threshold (−15 °C) of the fingers touching the stone surface, and 3.1 °C lower than the frostbite threshold (−18 °C). Frostbite might occur when fingers touch stone bricks, ice surfaces, and slide handrails.	Be cautious of touching cold surfaces, especially stone tiles, ice surfaces, and children’s handrails. Wear gloves. Anti-skid warning signs and emergency rescue stations should be set up on ice and snow fields and sites where stone bricks are laid. Regularly check the insulation coating of the touch area of the iron and steel facilities in the park.

lists the corresponding prevention strategies. The results of the whole-body cooling assessment showed that children performing light-intensity activities could only withstand the outdoor environment for 42 min. Therefore, they should increase metabolic heat production by exercising, wearing additional clothes, or moving indoors [83]. Subjects performing moderate-intensity activities can stay outside for longer. However, caregivers must ensure that the children do not get exhausted, perspire, or wear tight clothing [84]. They must focus on the cold risk that may be caused by local cooling. Subjects performing vigorous activities and wearing excessive clothing will perspire, accelerating the cooling rate of the body. Therefore, body temperature must be restored by changing to dry clothes or entering a temporary rest room in time to prevent hypothermia [63]. In addition, vigorous activities are more likely to cause respiratory heat loss, which is a major trigger for bronchoconstriction [82].

According to the local-cooling assessment, skin exposed to cold winds for a long time is at risk of cooling, especially in the OS, which was open and had a high wind speed. The risk level before 10:00 am was Level 2, with the skin at risk of freezing. Therefore, subjects in this space during this period should wear warm clothes, including scarves and hats with earmuffs, which can prevent frostbites [85]. The risk in all the other spaces during the test was Level 1. Therefore, caregivers should assist children in protecting their skin from cold winds, including having them wear gloves, scarves, stockings, masks, and hats with earmuffs. They should regulate the time subjects spend outdoors and avoid prolonged exposure to cold winds.

The assessment also found a risk of cold injuries on the floors of different materials and on the surfaces of playground equipment. Especially, children’s fingers may freeze over when they touch iron surfaces, icy surfaces, and stone bricks. Frostbite, which is associated with contact cooling, can be prevented by coating metal surfaces with an insulator or wearing contact gloves [83]. Therefore, the insulation coating of the contact area on iron and steel playground equipment (such as swings, slide handrails, railings, and seesaws) should be regularly checked. In spaces where children are prone to fall, such as ice rinks, and spaces where stone bricks are laid, anti-fall reminders and emergency telephones should be installed, among other measures.

4.4. Limitations and Future Research

This study has a few limitations. (1) COVID-19, limited research funding, and harsh outdoor environments in Harbin reduced the sample size. (2) The effects of individual differences other than sex among the subjects, such as age, thermal experience, and family background, on the thermal comfort and cold risk prevention were not analyzed. (3) Richer bioclimatic design strategies based on thermal benchmarks and safety have not been proposed, because of the lack of survey data for the summer and transition seasons. Richer multi-seasonal sample data, a more comprehensive thermal comfort factor analysis, and a spatial optimization design based on thermal benchmarks and safety in China’s severe cold regions should be considered in the future.

5. Conclusions

This study used meteorological monitoring, subjective thermal perception surveys, and activity records to explore the winter thermal benchmark and calendar for subjects in China’s severe cold regions. It also evaluated the cold risk faced by children while performing outdoor physical activities. Based on these evaluations, travel strategies and cold risk prevention strategies were tailored for the children. The main conclusions are as follows:

• In winter, the primary meteorological parameters affecting the children’s thermal perception are G, T_g, and T_mrt. Among them, G and T_g are the most important parameters affecting winter thermal sensation in male and female children in China’s severe cold regions. In the TCV, “comfortable” (49.8%), “neutral” (45.5%), and “uncomfortable” (4.8%) demonstrates the strong tolerance of children toward cold climates in China’s severe cold regions.
• In winter, female children exhibit lower NUTCI than male children (6.0 < 7.3 °C). The NUTCI of all children is 6.7 °C. The NUTCIR of female, male, and all children are −1.3–13.4, 0.6–14.1, and 0.5–14.0 °C, respectively. The minimum heat unacceptability ratio is greater than 20%. It indicates that the outdoor environment in the severe cold regions does not have comfortable thermal conditions for children in winter.
• In winter, the average I_cl of children engaged in light-intensity activities is less than ICL_min (1.88 < 3.9 clo). These children are at risk of whole-body cooling. The risk at the SP, SS, and SR is always under Level 1 (−24 ≤ t_WC ≤ −10 °C). OS has a risk level of Level 2 (t_WC ≤ −24 °C) before 10:00 a.m. The children touched wooden seats, plastic slides, and permeable bricks with their fingers, making them prone to the risk of pain. Touching stone bricks, ice surfaces, and slide handrails for more than 10 s may cause numbness and frostbite.
• At-risk subjects in these regions should receive more attention. More than 30% of the subjects experienced frostbite in different parts of the body. Approximately 16.6% had frostbitten ears, 14.8% had frostbitten fingers, and 2.5% had frostbitten toes. In addition, the subjects preferred exercising (P_Female = 35.5% and P_Male = 48.3%) and moving to sunshine (P_Female = 31.1% and P_Male = 26.4%) for thermal adaptation.
• To ensure that the children have a safer, more comfortable experience with outdoor physical activities in frigid regions, travel strategies based on thermal benchmarks and calendars were proposed. For example, children should exercise in children’s parks between 10:30 and 14:30 and choose the OS and SR with larger SVF and more solar radiation first. Additionally, the corresponding preventive strategies based on the cold risk assessment were proposed. For example, caregivers should assist children in protecting their skin from the cold, such as wearing gloves, scarves, stockings, masks, hats that can cover ears, and controlling the length of outdoor activities, avoiding prolonged exposure to cold wind. Moreover, gloves should be used to touch cold objects and falls should be avoided while outdoors.

The results reveal the factors affecting children’s thermal perception in winter in outdoor open spaces in China’s severe cold regions. They determine the risks of whole-body and local cooling in children. Based on this, a safer design strategy is of reference value to landscape designers and urban planners. Using deciduous trees instead of evergreen ones to not block the precious sunlight resources in winter is worth consideration. The volume and location of facilities in children’s activity space should be carefully decided to avoid unnecessary shelter from solar radiation. Windbreak belts or reasonable topography will help to block excessive prevailing winds at the site. Temporary shelters should be set up at a reasonable location in the park to ensure that children who have been out for a long time can recover their body temperature in time. Ice rinks, stone floors, and other relevant venues should be furnished with anti-fall warning signs to support children in understanding and avoiding the risk of localized cold such as frostbite. We anticipate that designers could draw greater design inspiration based on this research to ensure the safety and comfort of children in severe cold regions.