Development of a modified thermal humidity index and its application to human thermal comfort of urban vegetation patches

Figures & data

Figure 1. Location of the selected riparian buffer and its corresponding riverway in the Menchenghu city plain section of the Yongding river in Mentougou district of Beijing: (a) Beijing; (b) city plain section of the Yongding river in Beijing; and (c) selected riparian buffer and its corresponding riverway.

Table 1. Thermal category thresholds of thermal humidity index (THI), land surface temperature (LST), and modified thermal humidity index (MTHI).

THI^a	LST^b	MTHI	Physiological reaction ^c	Human thermal comfort level ^c
<21.1.	<28.5	<45.0	Suitable environment	1. Comfortable
[21.1, 23.8)	[28.5, 31.3)	[45.0, 55.3)	Most people have a slight heat sense	2. Slightly hot
[23.8, 26.6)	[31.3, 37.4)	[55.3, 72.6)	Heat exhaustion and heat stroke are possible	3. Hot
[26.6, 29.5)	[37.4, 40.0)	[72.6, 85.7)	Heat exhaustion is likely; heat stroke is possible	4. Very hot
≥29.5	≥40.0	≥85.7	Heat exhaustion and heat stroke are likely	5. Torrid

(a) From Mather (1974) and Wang and Shen (1998); (b) From Huang et al. (2013); (c) From Huang et al. (2013), Tahbaz (2011), and Wang and Shen (1998).

Figure 2. Modified thermal humidity index (MTHI) ranges and the corresponding human thermal comfort levels.

Figure 3. Methods to validate the estimated modified thermal humidity index (MTHI). Significance: ***p < 0.001.

Figure 4. Comparisons between the estimated modified thermal humidity index (MTHI) and estimated (HTC_m1 (a), HTC_m2 (b), HTC_m3 (c), HTC_m4 (d), and HTC_m5 (e)) and perceived human thermal comfort (HTC_s (f)). The relationships are also compared between MTHI and THI.

Figure 5. Daytime variations in measured microclimate indices and calculated thermal humidity indices for vegetation patches and roads in the study riparian buffer in July and August. The values at each time were from the mean measured or estimated data for the 47 vegetation patches, each having 18 (for T, RH, and THI) or 6 (for LST and MTHI) repeated measurements. Standard deviation bars are also provided.

Figure 6. Area portions of different human thermal comfort (HTC) levels at the daytime for the vegetation patches in the study riparian buffer in July (a), August (b), and September (c).

Figure 7. Estimated mean daytime modified thermal humidity index (MTHI) over the study subarea.

Figure 8. Redundancy analysis between microclimate indices and patch indices.

Figure 9. Comparisons of structure indices and their effects on modified thermal humidity index (MTHI) between different patches.

Table

Abbreviation	Full name
MTHI	Modified thermal humidity index
THI	Thermal humidity index
HTC	Human thermal comfort
WBGT	Wet-bulb globe temperature
T	Air temperature
RH	Relative humidity
LST	Land surface temperature
WS	Wind speed
VC	Vegetation coverage
TCD	Tree canopy density
AVC	Adjacent vegetation coverage
ATCD	Adjacent tree canopy density
NDR	Distance to river
PAR	Percent adjacent road
SEM	Structural equation modeling

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