High‐Resolution, Multilayer Modeling of Singapore's Urban Climate Incorporating Local Climate Zones

Mughal, Muhammad Omer; Li, Xian‐Xiang; Yin, Tiangang; Martilli, Alberto; Brousse, Oscar; Dissegna, Maria Angela; Norford, Leslie K.

doi:10.1029/2018jd029796

Cited by 73 publications

(63 citation statements)

References 81 publications

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“…This work used commercial satellite optical imagery to generate a 3-D model of urban form and vegetation across the entire city of Singapore, providing the data source to run radiative transfer simulations and modeling tasks at any desired location in the city. Such data has also been used in recent work on wind flow simulation and on a study of the urban climate of Singapore [34,35]. The accuracy of deriving tree height from satellite optical data remains low (3.5 m in this case).…”

Section: Discussionmentioning

confidence: 99%

3-D Reconstruction of an Urban Landscape to Assess the Influence of Vegetation in the Radiative Budget

Dissegna¹,

Yin

Wei

et al. 2019

Forests

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Increased urbanization and climate change have resulted in the intensification of the urban heat island (UHI) effect, particularly in tropical cities. One of the main causes of UHI is the man-made urban surfaces influencing the radiation budget by absorbing, reflecting, and emitting radiation at various wavelengths. The radiative budget of a city is directly influenced by the urban geometry, surface materials, direct solar radiation and incident angle, and atmospheric diffuse radiation. Vegetation cover, in contrast, can decrease UHI by intercepting radiation and through the process of photosynthesis. Better understanding the effect of urban vegetation on the radiative budget can thus contribute towards the mitigation of the UHI effect and ultimately the development of climate resilient urban spaces. To analyze the contribution of vegetation to the radiative budget of a city, a detailed simulation of the complex interaction between the built environment and the vegetation is required. This study proposes an approach for analyzing the 3-D structure of both vegetation and built environment to quantify the contribution of vegetation to the radiative budget of an urban landscape. In a first step, a detailed 3-D model of Singapore including buildings and vegetation was reconstructed using a combination of free and commercial Earth Observation data. Then, the 3-D Discrete Anisotropic Radiative Transfer (DART) model was repurposed to estimate the radiation absorbed by the urban surfaces accounting for the presence of vegetation cover with changing Leaf Area Density (LAD) conditions. The presence of trees in the scene accounted for a significant reduction of the absorbed radiation by buildings and ground. For example, in the case of a residential low-building neighborhood, although having low tree cover, the reduction of the absorbed radiation by buildings and ground was up to 15.5% for a LAD =1. The field validation shows good agreement (R2 = 0.9633, RMSE = 10.8830 and Bias = −1.3826) between the DART-simulated shortwave exitance and upwelling shortwave measurements obtained from a net radiometer mounted on a local flux tower in the urban area of Singapore, over the studied period. Our approach can be used for neighborhood-scale analysis, at any desired location of a city, to allow test scenarios with varying surface materials and vegetation properties.

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Section: Discussionmentioning

confidence: 99%

3-D Reconstruction of an Urban Landscape to Assess the Influence of Vegetation in the Radiative Budget

Dissegna¹,

Yin

Wei

et al. 2019

Forests

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“…The commenter misquoted Mughal et al (2019) that it was the first time the model was applied in a tropical city. Mughal et al (2019) clearly stated that there are other studies (Liao et al, 2014;Valdés, 2018;Wang et al, 2017) in the tropics which have utilized WRF/MLUCM.…”

Section: We Studied a Special Month With No Energy Balance Data Availmentioning

confidence: 99%

Reply to Comment by Velasco on “High‐Resolution, Multilayer Modeling of Singapore’s Urban Climate Incorporating Local Climate Zones”

Mughal

Yin

et al. 2021

JGR Atmospheres

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The research presented in Mughal et al. (2019) was supported by the National Research Foundation Singapore (NRF) under its Campus for Research Excellence and Technological Enterprise (CREATE) programme and its Intra-CREATE Collaborative Grant "Cooling Singapore." Overall, the commenter stressed validation, and indeed more validation is better. But in an urban context, with such large heterogeneity, it will be almost impossible to validate the model for all the different urban configurations. Even if the model is validated for a low-rise neighborhood of Singapore, it does not necessarily mean that the model will perform well for a high-rise, densely developed district. Similarly, obtaining temperature measurements in the urban canopy conforming with the standard requirement for urban measurement sitting (Oke et al., 2006) may be difficult due to the strong spatial variability of the temperature field. The spatial applicability of the point measurement in the canopy will be then limited, and, in principle, we could not directly compare point measurements of temperature against the 300-m spatial average provided by the mesoscale model. This means that in urban areas the model will be inevitably used for configurations where it has not been fully validated. But does this mean that model results are useless in these cases? We do not think so. Numerical models are grounded on physical principles and convey our best understanding of how the atmosphere interacts with the earth surface. They can be used to interpret measurements and to guide new field campaigns. If models show counterintuitive results in some places, this can be a motivation to perform dedicated field campaigns to check if the model is right, and if it is not these results can be used to improve the model formulation or setup. The commenter asserts that environmental point measurements are the "real world." This is generally true, but the information given by point measurements is necessarily incomplete in space and time. For many applications, we need a complete representation of the atmosphere in space and time, and this is something that, today, can be accessed only with models. A well-tested and well calibrated simulation model can be a good representation of the three-dimensional real world, its dynamics and its responses to the possible future perturbations (Zannetti, 1970). Even in environmental research, models are often validated against other models of different theoretical backgrounds as opposed to full-scale measurements; for example, computational fluid dynamics are usually tested against wind tunnel studies.

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“…Vegetation covers 56% of the total land area (Yee et al, 2011). The evapotranspiration's cooling effect and shade provided by trees have been widely investigated in Singapore, even by some coauthors of Mughal et al (2019), who have concluded that trees cannot be ignored to assess the local climate (Dissegna et al, 2019; Liu et al, 2017). However, in this study, Mughal et al did not consider the presence of trees.…”

Section: What About Evapotranspiration and Tree Shade?mentioning

confidence: 99%

“…In this context, the article of Mughal et al (2019) is a good example of how not to validate the performance of an urban climate model and how simplistic assumptions and wrong interpretations aiming to avoid the design of a holistic experiment do not help to understand the urban thermal climate.…”

Section: Introductionmentioning

confidence: 99%

Comment on “High‐Resolution, Multilayer Modeling of Singapore's Urban Climate Incorporating Local Climate Zones” by Mughal et al. (2019)

Velasco¹

2020

JGR Atmospheres

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Weather forecasting models coupled with canopy layer schemes are frequently used to assess the urban heat island (UHI) phenomenon through sensitivity analysis. These models are valuable tools if they are properly tested against field observations. Mughal et al. (2019) (https://doi.org/10.1029/ 2018JD029796) followed this approach to investigate Singapore's UHI effect within the urban canopy layer. But a lack of field observations for evaluating the model's performance led to simplistic assumptions and wrong interpretations. The major flaws triggered by both circumstances are exposed with the aim that future research does not repeat the same mistakes and can provide the scientific basis to formulate effective mitigation measures.

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High‐Resolution, Multilayer Modeling of Singapore's Urban Climate Incorporating Local Climate Zones

Cited by 73 publications

References 81 publications

3-D Reconstruction of an Urban Landscape to Assess the Influence of Vegetation in the Radiative Budget

3-D Reconstruction of an Urban Landscape to Assess the Influence of Vegetation in the Radiative Budget

Reply to Comment by Velasco on “High‐Resolution, Multilayer Modeling of Singapore’s Urban Climate Incorporating Local Climate Zones”

Comment on “High‐Resolution, Multilayer Modeling of Singapore's Urban Climate Incorporating Local Climate Zones” by Mughal et al. (2019)

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