INTRODUCTION

The needs for parks have long been realized as they provide venues for improving physical health, psychosocial well-being, self-actualization, spirituality and self-identity, family bonding, child development, environmental education and social skills development(Veal & Lynch, 2001). The importance of urban open spaces have been recognized both in the character and the life they bring to towns and cities around the world(Thompson, 2002). In recent times, changes in the climate due to global abnormalities have negatively affected the surrounding environment. In urban areas, changes in the weather are quite evident and the resulting deterioration in the weather environment has risked the health of urbanites(Her, 2013), as well as altered the number of hot and cold nights(Kim et al, 2011). Under these circumstances, green venues in the populated urban centers are of immense importance as they offer ecological and facility values, and improve environmental characteristics such as temperature reduction in the urban centers as well. The neighborhood parks play a positive role in promoting healthy environment as they relieves stress and serve as a rest and leisure spots for urbanites. These parks provides convenience in the living, and serves as a space that promotes the health of the citizens and as a result, the interest and demand for natural green spaces in the urban areas have risen(Konijnendijk et al, 2005;Kim et al, 2016;Park et al, 2017).

Among the functional aspects of green spaces in the cities, studies on weather control in particular has been given consistent attention. Such studies are often carried out on urban centers, where the weather conditions are deteriorating rapidly. There is a possibility that decrease in temperature may be achieved by manipulating the characteristics of urban green spaces. Such studies on temperature reduction in cities involve vegetation cover and geomorphic characteristics of the project area. The Seoul Metropolitan Government conducted a study in order to analyze the effect of mitigating heat island phenomenon of street trees through simulations, while another study was conducted to assess the impact of the street trees and street green areas on the city temperature(Kwon et al, 2012;Park et al, 2012). It was observed that the prime factors affecting the urban weather condition include the geomorphic characteristics and vegetation cover in the urban centers.

Keeping the importance of climate change and adverse effect of rising temperature on human health, we conducted the current study. In our study, we tried to assess the factors that affect the local weather by measuring the temperature, relative humidity, wind velocity and solar radiation. We also studied the role of vegetation cover and physical structures on the weather conditions of Gusan Neighborhood Park.

MATERIALS AND METHODS

1. Study Site

The Gusan Neighborhood Park is located in Mount Gusan-dong, Eunpyeong-gu, and it is a mountainous park in the city center(Figure 1&2). The park is at an altitude of 92 meters from sea level and covers an area is about 32,300 square meters. Compared to the small park area, the elevation is slightly higher, and there is a relatively steep promenade, and benches are built in the middle of the promenade. The vegetation cover include scattered trees comprising cherry, oak trees and others. Around the park, there are houses and social welfare facilities. The topography of Gusan Neighborhood Park consists of steep slopes because of the elevation difference as compared to the narrow area, while the topography of the ridge was generally distributed widely.

2. Methods

1) Research Procedure

In order to understand the impact of the vegetation and physical structure of the mountainous parks in the city center on the local weather, the topographical and vegetation structures were analyzed through preliminary research and on-site surveys. In topographic analysis, the elevation, gradient and aspect of the target site was analyzed through Auto Cad Map 2016 and QGIS(QGIS Desktop 3.6.1ver) using a numerical map of the national territory information map (2018). For analysis of plantation structure in the target area, the data collected from the field survey was investigated for the existing plant life, and further investigation of the diameter at breast height and the crown density were used in the analysis. For meteorological data, we observed temperature, relative humidity and wind speed by using the air velocity meter (TSI-9545, USA). The data was recorded 5 times taking into account the response speed of the heat flux sensor(LP02. Hukseflux) by exposing the sensor to the irradiation zone for 30 seconds. Short wave radiation (285-3,000 nm) was measured using Netherlands. For temperature measurement, we tried to minimize data fluctuations caused by wind direction by collecting data at a height of 1.2m above the ground with the wind behind.

2) Statistical Analysis

For statistical analysis was carried out by using SPSS(version 18.0). The variables used were temperature, wind speed, relative humidity and solar radiation as dependent variables. The existing vegetation, the slope, topography and plant life were taken as independent variables. One-way ANOVA was used to analyze the effects of changes in the physical and vegetation structure of the target site. For dependent variables with less than three variables, the analysis was performed through independent sample t-test. The influence of independent variables on the weather was also analyzed through route analysis. The plant life structure was selected based on the dominant tree species e.g. Quercus acutissima, Quercus mongolica, Quercus variabilis, Sorbus alnifolia and Robinia pseudoacacia. The variable number setting of the lung capacity was used for analysis by dividing it into variable number 1, 61 - 79% variable number 2, 80% variable number 3 as given(Table 1).

RESULTS AND DISCUSSION

1. Vegetation Cover of Gusan Neighborhood Park

The tree cover of the Gusan Neighborhood Park upper layer comprised of deciduous trees Robinia pseudoacacia, Quercus acutissima, Quercus mongolica, Quercus variabilis, and sorbus alnifolia. In subsurface types, Prunus sagentii was the dominant species. In the shrubby species, Stefanandra incisa was found dominant. It was also observed that the average diameter of the upper layer of the bridge deck was 20.42 cm, while the lowest was recorded as 22 cm. The minimum thoracic diameter recorded was 6cm, while 26cm was the maximum size. On the average, 76.92% of the total vegetation were analyzed in the park. In previous studies conducted on neighborhood parks and urban green areas, reported the positive correlation of greenery and a subsequent decrease in the temperature(Kim et al, 2018a;Park et al, 2017).

2. Effect of Vegetation on Microclimate of the Park

1) Impact of Vegetation on Park Climate

We used 5 plant species colony Quercus acutissima, Quercus mongolica, Quercus variabilis, Sorbus alnifolia and Robinia pseudoacacia as test trees to evaluate the correlation of these trees with temperature, relative humidity, wind speed and solar radiations as shown in table 2. We observed that minimum temperature(25.3°C) was recorded for Quercus acutissima while highest temperature of 26.98°C was observed for Sorbus alnifolia (Table 2). We recorded highest relative humidity (70.4%) for Robinia pseudoacacia, lowest wind speed (0.24㎧) for Quercus mongolica and minimum solar radiations(44.6 W/ ㎡) for Sorbus alnifolia(Table 2). We observed that the relative humidity was lower in the trees grown on upper ridges, while it was higher in tree stands located in the foothills. The wind speed and solar radiations were also higher in Quercus species.

2) Impact of Diameter at Breast Height(DBH) on Park Climate

Current study confirmed the impact of tree DBH on the environment of urban parks. It is quite evident from the significant probability of less than 0.01 in temperature and solar irradiance, excluding relative humidity. This led to the rejection of the null hypothesis that there was no difference between the temperature and the sun radiations due to the difference in the diameter of the thoracic region, and the alternative theory that the temperature and the sun radiations were different in at least one type was adopted. On the other hand, it was analyzed that changes in wind velocity due to thoracic diameter were significant at the level of 0.05, and the alternative theory was adopted that differences in wind speed were found in at least one type according to the difference in thoracic diameter. However, a null hypothesis was adopted that for relative humidity among the items measured, the probability of significance was analyzed to be greater than 0.05 and that significance was not verified, so there was no change in the mean value for relative humidity due to differences in the thorax diameter. It was concluded that the temperature, wind speed, and solar irradiance vary depending on the DBH, and that the relative humidity is somewhat unaffected by the tree stem diameter.

3) Impact of Tree Crown Density on Park Climate

We observed that the tree crown density greatly affected the temperature, humidity, wind speed and solar radiations as shown in table 5. The lowest temperature(25.4℃) was recorded for crown density of more than 80% while highest (26.38℃) for crown density of less than 60%. In case of humidity and wind speed, the maximum values were recoded for more than 80% crown density(Table 5). The solar radiation analyzed showed least data for maximum tree crown density. The parameters studied showed significant values except wind speed, and this demonstrated that the effect of crown density on the weather factors is significant.

We carried out one-way ANOVA of the crown density to explain the effect of crown density on weather factors with statistical support(Table 6). The variables were set at variable numbers lees than 60%, 60% to 80% and more than 80% respectively. The analysis confirmed significance of the temperature and the solar radiation with a significant probability of 0.01 or lower, rejecting the null hypothesis that there was no difference in the meteorological environment measurement values due to the differences in the crown density, and adopting the alternative hypothesis that at least one type of difference was caused by the difference in the crown density. On the other hand, the null hypothesis was adopted that there was no change in the average value for relative humidity and wind speed due to differences in crown density as significance was not noticed for probability of 0.05% or above, for relative humidity and wind speed.

3. Effect of Park Topography on Environmental Factors

1) Correlation of Elevation with Climate of Park

Current study showed that temperature of the park was not significantly affected by terrain elevation as shown in table 7. However, maximum relative humidity(70.75%) was recorded for mountain foot while least for hill top (table 7). The maximum wind speed of 0.37 m/s was observed on hill top, while the hill side was found to be exposed to least solar radiations as shown in table 7. The temperature changes according to the elevation difference showed no significance, while the relative humidity was least on hill top probably because the hill tops are exposed to wind. Our results are similar and confirms previous studies reporting lower relative humidity and highest wind speeds on elevated terrains(Kim et al, 2012;Choi et al, 2006).

The One-Way ANOVA demonstrated the effect of terrain on the climate factors. The analysis showed the significant probability for temperature(0.161), and confirmed the null hypothesis that changes in elevation do not affect the temperature in neighborhood parks. In case of relative humidity, the alternative hypothesis was adopted that the change in relative humidity caused by the difference in elevation, at least one group gives significantly lower result probability level 0.05. For both wind speed and solar radiation, a significant probability was analyzed at 0.01 level, rejecting the null hypothesis that there was no difference in the measured values due to differences in elevation, and adopting a counter-argument that the difference in elevation affected the wind speed and the solar radiation as shown in table 8.

2) Correlation of Mountain Slope with the Climate of the Park

Current study showed that mountain slope do play an important role in determining climate of neighborhood parks. The temperature, relative humidity and solar radiations were significantly affected by the slope gradient, although wind speed was not significantly affected as shown in table 9. According to the slope gradient, we observed that there are significant differences between types of weather factors except wind speed, and overall, the higher the gradient, the higher the temperature and wind speed, and the lower relative humidity.

One-way ANOVA was performed with three slope variables i.e. less than 10°, 10° - 30° and above 30° gradient respectively in order to determine the effect of difference in slope gradient on the climate factors. The analysis proved significant at 0.01 level for the temperature, wind speed and solar irradiance, thus rejecting the null hypothesis that there was no difference in climate factors due to varying slope gradient. However, for relative humidity, the null hypothesis that the relative humidity does not change due to the difference in gradient was confirmed, although the differences in other climate factors were significant with changing slope gradient(Table 10).

3) Correlation of Aspect and Climate Factors of Park

The aspect plays an important role in vegetation cover, temperature, humidity and other climate factors. In current study, we observed that the temperature, wind speed and solar radiations were not significantly affected by aspect(shown in Table 11). However, relative humidity was significantly affected and maximum relative humidity of 70.97 % was recorded for north facing slope while least for south facing slope(Table 11). This difference is due to the fact that the south facing slope is exposed to sunlight for longer period as compared to north facing slopes.

In order to understand the effect of the aspect on the weather conditions, we used 4 variables i.e. north facing slopes, east facing slopes, south facing slopes and west facing slopes. The statistical analysis rejected the null hypothesis that there was no significant changes in temperature and relative humidity values at 0.01 probability level. However, for wind speed and solar radiation, the probability of significance was analyzed to be greater than 0.05 and the null hypothesis was adopted that there was no change in the average value due to the difference in the direction of the slope. Differences in weather factors due to differences in aspect were significant in relative humidity, but the changes in temperature, wind speed and solar radiation were insignificant under different aspects(Table 12).

4) Correlation of Park Terrain with Climate Factors

In current study, we observed that the temperature, wind speed and solar radiations were not significantly affected by the varying park terrain(shown in Table 13). However, relative humidity was significantly affected and maximum relative humidity of 70.89 % was recorded for the valley(Table 13).

To understand the effect of terrain on the environmental factors, three variables that is Valley, Slope and Ridge were subjected to One-way ANOVA. The statistical analysis rejected the null hypothesis that there was no difference in the values due to the difference in the terrain structure as significant probability was less than 0.01 and adopted the alternative hypothesis that differences in terrain structure resulted in differences in at least one type i.e. relative humidity, but the differences were insignificant in all other factors studied(Table 14).

4. Overall impact of vegetation and physical patterns on the climate factors of park

In current study, we investigated the impact of vegetation and physical features of the Gusan neighborhoods park on the temperature, relative humidity, wind speed and solar radiations of the park. Our study showed that the effect of two physical patterns i.e. elevation and topographical structure (p>0.05) was not significant on temperature, and the slope gradient was correlated at significant probability of 0.01 level. Overall, the changes in the temperature of urban neighborhood parks were significant under the influence of slope gradient, DBH, the stern diameter, and the terrain elevation. On the other hand, relative humidity was significantly affected with varying elevation, slope gradient, aspect, and vegetation cover. In the case of wind speed, there was a correlation of wind speed with the elevation in the physical structure (p<0.01), but no statistical significance was observed in the slope gradient, aspect and terrain structures at p<0.05(Figure 3). The DBH analyzed showed very high correlation between temperature and solar radiation, but little correlation with wind speed.