Study on the influencing factors and the spatiotemporal heterogeneity of Urban Heat Island effect in Nanchang City of China

Figures & data

Figure 1. The geographical location of Nanchang and research area.

Figure 2. Workflow in this study.

Figure 3. Spatiotemporal distribution characteristics of the UHI effect in Nanchang city: (a)-(c) 2000, 2010, and 2019, respectively.

Table 1. Impact indexes of the UHI effect in Nanchang city.

Type	Impact indexes	Description	Unit
Topography factors	Digital Elevation Model (DEM)	DEM average within each grid	m
	Slope	Slope average within each grid	-
Vegetation factors	Normalized difference vegetation index (NDVI)	NDVI average per grid	-
Buildings factors	Normalized Difference Built-up Index (NDBI)	NDBI average per grid	-
Bare land (soil) factors	Soil Brightness Index(NDSI)	NDSI average per grid	-
Socioeconomic factors	Night-lighting(NL)	NL average within each grid	-

Table 2. Classification of the UHI effect.

UHIEI	UHIEI grade	UHI effect	Abbreviation
≤0	1	Green island effect	GIE
0 ~ 0.05	2	Weak green island effect	WGIE
0.05 ~ 0.1	3	Medium heat island effect	MHIE
0.1 ~ 0.2	4	Relatively strong heat island effect	RSHIE
0.2 ~ 0.3	5	Strong heat island effect	SHIE
≥0.3	6	Extremely strong heat island effect	ESHIE

Figure 4. Profile map of the UHIEI in Nanchang city with 2000, 2010, and 2019: (a), (b), (c), and (d), respectively.

Table 3. Statistics on the UHI effect of Nanchang in 2000, 2010 and 2019.

Year	Unit	UHI effect
		GIE	WGIE	MHIE	RSHIE	SHIE	ESHIE
		≤0	0 ~ 0.05	0.05 ~ 0.1	0.1 ~ 0.2	0.2 ~ 0.3	≥0.3
2000	km^2	421.77	303.54	346.54	656.89	194.91	39.84
	%	21.48	15.46	17.65	33.45	9.93	2.03
2019	km^2	480.15	225.32	321.38	687.92	181.38	67.34
	%	24.45	11.48	16.37	35.03	9.24	3.43
2000–2019	km^2	58.39	−78.23	−25.17	31.04	−13.53	27.50
	%	2.97	−3.98	−1.28	1.58	−0.69	1.4

Table 4. The OLS model regression results and diagnostics for 2000, 2010, and 2019.

Year	AICc	R-squared	Adjusted R-squared	F-Statistic	Jarque-Bera	VIFmax
2000	−2761.918	0.599	0.597	285.242	24408.115	4.728
2010	−2713.148	0.356	0.353	105.457	3036.719	5.613
2019	−3116.376	0.648	0.646	351.188	740.077	7.539

Table 5. Results and diagnostics of the GWR analysis in 2000, 2010, and 2019.

Year	Bandwidth	ResidualSquares	EffectiveNumber	Sigma	AICc	R-squared	Adjusted R-squared
2000	9255.611	2.699	62.523	0.050	−3611.916	0.821	0.811
2010	9195.802	2.656	66.823	0.049	−3624.014	0.729	0.713
2019	8827.790	2.693	71.033	0.050	−3601.189	0.787	0.773

Figure 5. Spatial distribution of the local R² in GWR Model of Nanchang City: (a)-(c) 2000, 2010, and 2019, respectively.

Figure 6. Regression coefficient of topography and vegetation factors in GWR models: (a)-(c) 2000, 2010, and 2019, respectively.

Figure 7. Regression coefficient of buildings, bare land, and social-economic factors in GWR Models: (a)-(c) 2000, 2010, and 2019, respectively.

Table 6. Descriptive statistics of regression coefficients of GWR models for 2000, 2010, and 2019.

	2000					2010					2019
Variables	Mean	Max	Min	SD	Median	Mean	Max	Min	SD	Median	Mean	Max	Min	SD	Median
DEM	0.0011	0.0054	−0.0006	0.002	−0.0001	0.0017	0.0119	−0.0007	0.003	−0.0001	0.001	0.0049	−0.0004	0.0015	−0.0001
Slope	0.0021	0.0146	−0.0054	0.0048	0.0008	−0.004	0.0094	−0.022	0.0057	−0.0036	−0.0031	0.0096	−0.0194	0.0058	−0.0019
NDBI	0.2107	0.6181	−0.3989	0.198	0.2614	−0.0278	0.1668	−0.2717	0.1027	−0.0298	0.4628	0.9332	0.0159	0.1993	0.4564
NDVI	0.0973	0.2706	−0.0243	0.0654	0.0982	0.3279	0.781	−0.0912	0.2333	0.3426	0.0425	0.1913	−0.0649	0.0484	0.0369
NDSI	0.6316	1.9577	−0.2264	0.4946	0.5215	0.7043	1.4227	−1.0091	0.4614	0.7768	0.1563	1.0212	−0.2796	0.2917	0.1227
NL	0.0028	0.0308	−0.0008	0.0037	0.0022	0.0009	0.0022	−0.0014	0.0009	0.0012	0.0013	0.0068	−0.0014	0.0014	0.0011

Table

Terminology
UHI		Urban Heat Island	LST	Land Surface Temperature
GIE		Green Island Effect	WGIE	Weak Green Island Effect
MHIE		Medium Heat Island Effect	RSHIE	Relatively Strong Heat Island Effect
SHIE		Strong Heat Island Effect	ESHIE	Extremely Strong Heat Island Effect
UHIEI		relative UHI effect intensity	RS	Remote Sensing
TIR		thermal infrared	GIS	Geographic Information System
VIF		Variance Inflation Factor	GDP	Gross Domestic Products
Max		Maximum	Min	Minimum
SD		Standard Deviation	AICc	Akaike information criterion
Variable
NDVI	Normalized difference vegetation index		NDBI	Normalized Difference Built-up Index
NDSI	Soil Brightness Index		NL	Night-Lighting
DEM	Digital Elevation Model
Model
OLS	Ordinary Least Squares		GWR	Geographically Weighted Regression