Estimation of the Relationship between Urban Park Characteristics and Park Cool Island Intensity by Remote Sensing Data and Field Measurement
Abstract
:1. Introduction
2. Methods
2.1. Study Sites
2.2. Data Preparation
2.2.1. Urban Park Characteristics
2.2.1.1. Urban Park Size and Shape
2.2.1.2. Urban Forest Structures in Parks
- Stem density (SD): It is defined as the number of trees (N) per unit area (Equation 1).
- Diameter at breast height (DBH): The DBH was measured directly by optical instruments. Their value in a sampling quadrat is the average of DBH values for all sampled trees (Equation.2).
- Tree height (H): The H was also measured directly by optical instruments. Their value in a sampling quadrat is the average of H values for all sampled trees (Equation 3).
- Base area (BA): Basal area is defined as the ratio of the cross-sectional area of all trees in a sampling quadrat to the ground area they occupy. It was calculated from DBH and the value of base area is the total BA values of all sampled trees per unit area in a sampling quadrat (Equation 4).
- Canopy density (CD): CD was measured directly with a fish-eye camera, which is defined as the ratio of the fractional area (projected vertically) of urban forest canopy in a sampling quadrat to the ground area it occupies.
- Leaf area index (LAI): LAI was also measured directly with a fish-eye camera and TRAC, which is defined as the ratio of the leaf areas in a sampling quadrat to the ground area they occupy.
2.2.2. Park Cool Island (PCI) Intensity
Season | Summer | Autumn |
---|---|---|
Data of TM acquisition | June 5, 2011 | September 22, 2010 |
Time of TM acquisition | 10:12 a.m. | 10:11 a.m. |
Min air temperature(°C) | 21.6 | 4.6 |
Max air temperature(°C) | 31.2 | 21.6 |
Mean air temperature(°C) | 26.4 | 14.3 |
2.3. Statistical Analyses
3. Results
3.1. Descriptive Statistics of PCI and Urban Park Size
Park | Area(ha) | Perimeter(m) | PCI(°C) | Plot | |
---|---|---|---|---|---|
Summer | Autumn | ||||
1 | 324.64 | 8737.28 | 8.96 | 7.17 | 13 |
2 | 75.86 | 3852.54 | 6.39 | 5.85 | 9 |
3 | 15.98 | 1806.08 | 5.73 | 4.80 | 4 |
4 | 7.02 | 1115.03 | 3.92 | 3.76 | 3 |
5 | 3.08 | 781.84 | 2.59 | 2.67 | 2 |
6 | 23.90 | 2259.43 | 5.43 | 4.30 | 6 |
7 | 4.37 | 871.87 | 4.48 | 4.94 | 4 |
8 | 14.92 | 1549.77 | 5.00 | 3.70 | 5 |
9 | 11.74 | 1625.92 | 4.81 | 4.63 | 3 |
10 | 23.57 | 1980.82 | 4.43 | 4.67 | 6 |
11 | 69.06 | 3928.14 | 4.81 | 3.48 | 9 |
12 | 25.09 | 2086.32 | 4.94 | 2.28 | 3 |
13 | 13.20 | 2396.81 | 4.68 | 3.99 | 3 |
14 | 13.45 | 1873.13 | 5.37 | 3.98 | 4 |
15 | 9.07 | 1261.56 | 4.43 | 4.02 | 6 |
16 | 23.17 | 2194.94 | 6.01 | 5.09 | 8 |
17 | 18.50 | 1739.95 | 4.55 | 2.91 | 4 |
18 | 8.88 | 1334.59 | 6.71 | 4.95 | 6 |
19 | 44.32 | 2821.94 | 6.10 | 6.26 | 7 |
20 | 29.87 | 2302.04 | 5.82 | 5.31 | 5 |
21 | 87.23 | 3783.27 | 5.80 | 3.64 | 7 |
22 | 3.38 | 811.09 | 3.60 | 1.40 | 2 |
23 | 210.00 | 6001.00 | 7.90 | 6.84 | 8 |
24 | 43.97 | 2921.70 | 3.29 | 3.41 | 4 |
25 | 4.34 | 743.88 | 2.24 | 3.15 | 1 |
26 | 1.90 | 494.45 | 1.24 | 1.02 | 1 |
27 | 3.89 | 704.25 | 2.37 | 1.64 | 2 |
28 | 1.47 | 432.73 | 0.51 | 1.36 | 1 |
29 | 15.30 | 1607.08 | 3.68 | 2.76 | 5 |
30 | 4.52 | 1229.70 | 1.65 | 1.58 | 3 |
31 | 10.70 | 1345.53 | 4.27 | 3.63 | 4 |
32 | 159.93 | 5924.30 | 5.56 | 4.86 | 7 |
33 | 57.60 | 3212.77 | 1.93 | 0.34 | 3 |
3.2. Effects of Urban Park Size on PCI Intensity
3.3. Effects of Urban Park Shape and Forest Structures in Parks on PCI Intensity
Park | Summer | Autumn |
---|---|---|
Area (ha) | 0.626** | 0.549** |
Perimeter (m) | 0.685** | 0.587** |
Perimeter/Area (m/ha) | −0.715** | −0.584** |
Forest structure | Summer | Autumn |
---|---|---|
Stem density (n/ha) | 0.563** | 0.201 |
Diameter (cm) | 0.584** | 0.532* |
Tree Height (m) | 0.666** | 0.440 |
Basal Area (m2/ha) | 0.707** | 0.574** |
Leaf area index | 0.722** | 0.658** |
Canopy density (%) | 0.806** | 0.747** |
Forest structure | Summer | Autumn | ||
---|---|---|---|---|
Regression Model | R2 | Regression Model | R2 | |
Stem density (n/ha) | y = 0.1012x + 2.7347 | 0.3163 | y = 0.0375x + 3.3474 | 0.0408 |
Diameter (cm) | y = 0.1332x + 3.1482 | 0.3419 | y = 0.1250x + 2.331 | 0.2826 |
Tree height (m) | y = 0.3554x + 2.5021 | 0.4432 | y = 0.0023x + 2.4892 | 0.1717 |
Basal area (m2/ha) | y = 0.1028x + 3.4094 | 0.5011 | y = 0.0871x + 2.7413 | 0.3371 |
Leaf area index | y = 0.2397x + 3.1915 | 0.5225 | y = 0.2254x + 2.369 | 0.4330 |
Canopy density (%) | y = 5.1905x + 1.9268 | 0.6507 | y = 4.7961x + 1.3199 | 0.5578 |
4. Discussion
4.1. Theoretical Implications
4.2. Management Implications
5. Conclusions
- (1)
- Urban parks can create PCI effects. However, the PCI intensity varied across seasons and the cooling effect of parks in summer was higher than that in autumn.
- (2)
- Urban park size was the most important factor for mitigating UHI, and increases in urban park size were still an effective measure to mitigate UHI.
- (3)
- Not only does urban park size but also urban park shape significantly affects PCI intensity. Given a fixed size of urban park, LST can be significantly increased or decreased by the different shapes of an urban park. Our results showed that the rounder the urban park shape is, the better the cooling effect achieved. Besides, urban forest structures also had significant impacts on the cooling effects of urban parks, among which the canopy density and LAI were the most effective in cooling. So, the trees, shrubs and grass should be designed in optimal ways to increase canopy density and LAI to maximize the cooling effect of urban parks. Therefore, UHI can be mitigated by optimizing urban park shape and forest structures when undertaking urban park planning, especially in cities where land resources are too limited to increase urban park size.
- (4)
- The relationship in summer between PCI intensity and urban park characteristics was stronger than that in autumn. Urban park characteristics may play a more important role in mitigating urban heat islands in summer than in autumn.
Acknowledgments
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Ren, Z.; He, X.; Zheng, H.; Zhang, D.; Yu, X.; Shen, G.; Guo, R. Estimation of the Relationship between Urban Park Characteristics and Park Cool Island Intensity by Remote Sensing Data and Field Measurement. Forests 2013, 4, 868-886. https://doi.org/10.3390/f4040868
Ren Z, He X, Zheng H, Zhang D, Yu X, Shen G, Guo R. Estimation of the Relationship between Urban Park Characteristics and Park Cool Island Intensity by Remote Sensing Data and Field Measurement. Forests. 2013; 4(4):868-886. https://doi.org/10.3390/f4040868
Chicago/Turabian StyleRen, Zhibin, Xingyuan He, Haifeng Zheng, Dan Zhang, Xingyang Yu, Guoqiang Shen, and Ruichao Guo. 2013. "Estimation of the Relationship between Urban Park Characteristics and Park Cool Island Intensity by Remote Sensing Data and Field Measurement" Forests 4, no. 4: 868-886. https://doi.org/10.3390/f4040868