Abstract
Abstract. This paper analyzed both the horizontal and vertical extent of air temperature variations as affected by vegetation leaf area density (LAD) and building area per height threshold. The current microclimate (Scenario 1) and two potential future urbanization scenarios in Lower Session Road, Baguio City were simulated with ENVI-met. The future scenarios include the removal of the Balete trees in the median strip (Scenario 2), and removal of some pine trees and addition of new buildings in the study site (Scenario 3). Remotely-sensed data were used in creating the primary model inputs including the initial built-up layer from PlanetScope green-based built-up index (VgNIR-BI), and digital elevation models (DEM) and normalized difference vegetation index (NDVI) maps derived from unmanned aerial system (UAS) for tree canopy mapping. The horizontal variations in air temperature were observed by selecting three subsites with different proximity to the adjusted variables, while vertical analysis was done by comparing the temperature values from the near-ground up to the 20m height range. Very minimal temperature change (0 °C to −0.01 °C) was observed between the current and simulated scenarios when average temperature of the whole site is obtained. However, temperature variations were better observed with per-subsite analysis as the effects of the adjusted variables are seen to be localized and restricted only to the surrounding thermal condition. Air temperature is highest within 12:00 to 13:00 hours for the three scenarios. In the current scenario, the right region of the study site is cooler in the morning, which gradually became warmer pre-noon up to late afternoon. Removal of Balete trees with Scenario 2 have increased the temperature in the near-ground elevation only, both in Subsites 1 (up to 0.1 °C) and 3 (up to 1.6 °C), attributed to the loss of surface shadow and reduction in total LAD. In contrast, the removal of pine trees and addition of buildings impacted the air temperature across all subsites and across all atmospheric height ranges. Application of Scenario 3 to Subsite 3 which is close to the adjusted variables, gave the highest near-ground air temperature rise across the study site with a mean value of 1.4 °C and a maximum value of 1.9 °C. The ENVI-met model of the current scenario generated high accuracy (R2 = 0.59 to 0.99) which implies that the simulation outputs are reliable for this study.
Highlights
Several studies confirmed that the presence of built-up area can accelerate the effect of Urban Heat Island (UHI), whereas water and green spaces can reduce the UHI intensity
The current study aims to stimulate the local current microclimate conditions in Lower Session Road Baguio City, and to determine the impact of (a) removing the Balete vegetation in its median strip, and (b) removing a number of pine trees and adding more built-up structures throughout the study area
Most of the pine trees have 10m to 12m tree height, resulting to the highest decrease in leaf area density (LAD) at this level. It was followed by the difference in LAD at 0.2m height which is mainly attributed to the removed grass
Summary
Several studies confirmed that the presence of built-up area can accelerate the effect of Urban Heat Island (UHI), whereas water and green spaces can reduce the UHI intensity. The current study aims to stimulate the local current microclimate conditions in Lower Session Road Baguio City, and to determine the impact of (a) removing the Balete vegetation in its median strip, and (b) removing a number of pine trees and adding more built-up structures throughout the study area. These two scenarios will more likely to happen in the future due to the continuous rate of urbanization, and modelling the impacts will aid in drawing the necessary mitigation actions. Three subsites were selected to better observe the localized effect of each selected scenario, in addition to the mean air temperature variations across the whole study area
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