Effects of vegetation covers for outdoor thermal improvement: A Case Study at Abubakar Tafawa Balewa University, Bauchi, Nigeria

Abdulkarim, Kabiru Haruna; Ghafar, Azmiah Abd; Lai, Lee Yoke; Said, Ismail

doi:10.47836/pjst.29.3.43

Cited by 2 publications

(2 citation statements)

References 43 publications

(57 reference statements)

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“…FLUENT was used to simulate air turbulence in an ideal urban green space condition in Guangzhou (Feng and Chu, 2017). Previous studies using ENVI-met have found that outdoor thermal improvements in campus areas are related to the effects of different levels of tree canopy closure in Nigeria (Abdulkarim et al, 2021). Liu et al (2018) set up simulation experiments using ENVImet.…”

Section: Introductionmentioning

confidence: 99%

Microclimate effects and influential mechanisms of four urban tree species underneath the canopy in hot and humid areas

Feng

Huang²,

He³

et al. 2023

Front. Environ. Sci.

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Purpose: Urban trees play a key role in ameliorating extreme urban climates in cities. At the micro-level, it is crucial to investigate the variations in microclimates affected by the canopies of different tree species. The significance of this research is to provide scientific evidence for the selection of tree species in urban planning that can improve the local microclimate. This study examines the factors of microclimate (air temperature, relative humidity, wind environment, and solar radiation) underneath the canopy of four different evergreen tree species in hot and humid areas. Furthermore, the correlation between the physiological characteristics of these tree species and microclimate was statistically analyzed using data on the physiological parameters of the trees and microclimate factors.Methods: In this study, four tree species were selected for field measurements: Ficus microcarpa L. f., Ficus virens Aiton, Bauhinia x blakeana Dunn, and Cinnamomum camphora (L.) Presl. We used the HOBE (H21-0024, onset) to measure three climatic parameters (Temperature, Relative Humidity, and Instantaneous Wind Speed), and the Li-6400 Portable Photosynthesis System to measure five plant physiological parameters: Stomatal Conductance (Gs), Leaf Temperature (Tleaf), Leaf Surface Relative Humidity (RHsfc), Photosynthetically Active Radiation (PAR), and Leaf-level Vapor Pressure Deficit (Vpdl). The observations were conducted during winter (January 16 - January 22) and summer (August 7 - August 22). The investigation periods were 9:00–11:00, 12:00–14:00, and 16:00–18:00, and data were recorded at 15-min intervals. The observational data obtained were analyzed using statistical methods, including one-way analysis of variance, Pearson correlation coefficient, and multiple regression analysis.Results: The results of this study indicated that the four tree species being measured had different effects on the microclimate at the sites in both the winter and summer seasons. During the 7-day observation in the summer, the cooling effect of the four tree species was significant. The relative humidity underneath the canopies was 3%–11% higher than that of weather stations. The instantaneous wind speed in the afternoon was relatively higher than at other times. The solar radiation intensity was dramatically reduced by 85%–95%. During the 7-day observation in the winter, the trees had a warming effect in the morning. The relative humidity underneath the canopies was 10%–20% higher than that of the weather stations. The areas underneath the canopies were windless in the afternoon. The solar radiation intensity was reduced by 78%–95%. Ficus microcarpa was found to be one of the most effective tree species for increasing the relative humidity and reducing solar radiation intensity in hot and humid areas. Additionally, the highest instantaneous wind speed was observed in the areas underneath the canopies of F. virens and C. camphora. Statistical tests revealed that the air temperature and the instantaneous wind were extremely significantly correlated with Tleaf and RHsfc.Conclusion: The four urban tree species studied had varying degrees of effect on air temperature, relative humidity, wind speed, and reducing solar radiation intensity in the areas underneath their canopies. Furthermore, these trees demonstrated varying abilities to improve microclimate conditions in different seasons. The four trees had a cooling effect in the summer. The instantaneous wind speed was calm in the afternoons during the winter in contrast to being relatively high speed in the afternoons during the summer. This characteristic is beneficial to warmth in winter and coolness in summer. In terms of the internal influence mechanisms, the results of the analysis indicated that microclimate factors were significantly correlated with the physiological parameters of the trees. Tleaf, RHsfc, and Vpdl were significant physiological parameters and had different contribution rates to microclimate factors.

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Section: Introductionmentioning

confidence: 99%

Microclimate effects and influential mechanisms of four urban tree species underneath the canopy in hot and humid areas

Feng

Huang²,

He³

et al. 2023

Front. Environ. Sci.

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“…Increased tree canopy coverage effectively reduced air temperature and mean radiant temperature in urban residence, with air temperature and mean radiant temperature with high tree canopy coverage reduced by 3.3 • C and 13.9 • C, respectively, compared to urban residence with no tree canopy coverage [23]. A study in Nigeria showed that outdoor air temperature could be reduced by up to 3.38 • C and mean radiant temperature by up to 24.24 • C when 45 percent of the canopy was covered with trees [24]. Based on the consideration of thermal dynamics and human thermal comfort, the study quantified the maximum effective canopy cover thresholds of 45 percent, 30 percent, and 25 percent for residential areas of 33 m (11 floors), Forests 2024, 15, 518 3 of 23 54 m (18 floors), and 100 m (33 floors) in height, respectively [25].…”

Section: Current Research Perspectives On Greenery In Residential Areasmentioning

confidence: 99%

A Study on the Effect of Green Plot Ratio (GPR) on Urban Heat Island Intensity and Outdoor Thermal Comfort in Residential Areas

Zheng,

Li,

Zheng

2024

Forests

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Greenery impacts the urban thermal environment, but the benefits of the three-dimensional green volume of space have not been effectively evaluated. In this paper, we analyzed the impact of 3D greenery on urban heat island intensity and thermal comfort in residential areas from the perspective of the green plot ratio (GPR). We selected a typical residential area, set up simulation models, and then analyzed the effect of different GPR values on the outdoor thermal environment using the validated ENVI-MET simulation. The results showed that increasing GPR in residential areas can effectively reduce the intensity of urban heat island and improve thermal comfort. When the GPR reaches 0.5 and 1.5, the thermal comfort level of the building overhead space and the north–south street space decreases from “very strong thermal stress” to “strong thermal stress”. When the GPR reaches 2.5, the outdoor thermal comfort of the east–west street space and courtyard space is reduced to “hot”. When the GPR is higher than 0.5, the urban heat island intensity in the north–south street space decreases by one level, from “very strong” to “strong”. When the GPR reaches 3.5, all four types of spaces have “moderate” urban heat island intensity. Increased GPR exacerbates urban heat island intensity to some extent and worsens outdoor thermal comfort due to the nocturnal insulating effect of plants. Based on the results, the study proposes the bottom-line control of the GPR index from the perspective of urban heat island mitigation and thermal comfort improvement. This paper points out the benefits of GPR in residential areas in improving the human environment, which is of great practical value for developing urban residential environment from “increasing quantity” to “improving quality”.

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Effects of vegetation covers for outdoor thermal improvement: A Case Study at Abubakar Tafawa Balewa University, Bauchi, Nigeria

Cited by 2 publications

References 43 publications

Microclimate effects and influential mechanisms of four urban tree species underneath the canopy in hot and humid areas

Microclimate effects and influential mechanisms of four urban tree species underneath the canopy in hot and humid areas

A Study on the Effect of Green Plot Ratio (GPR) on Urban Heat Island Intensity and Outdoor Thermal Comfort in Residential Areas

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