Climate Modelling and Analytics for Urban Heat Risks Mitigation and Adaptation

This study highlights the need for climate-sensitive urban planning and design in the face of climate change, with a specific focus on Singapore. Rapid urbanization has led to significant warming trends, increased heat stress, and heightened electricity demand for cooling. The Urban Climate Design Lab (UCDL) at the National University of Singapore employs a multidisciplinary approach, merging urban planning, architecture, and urban climate science. The research introduces GIS-based tools to evaluate the microclimate impact of new developments, replacing time-consuming simulations and wind tunnel experiments. These tools encompass: 1) The Urban Wind Environment Model, assessing urban permeability for natural ventilation; 2) The Fine-Scale Wind Environment Model, providing high-resolution pedestrian-level wind speed data. 3) The Urban Tree-Airflow Model, aiding tree placement and species selection for optimal cooling. 4) The Anthropogenic Heat Dispersion Model, estimating the impact of human-generated heat emissions. These GIS tools are integrated into the open-access UCDL Microclimate Digital Platform, facilitating knowledge transfer and empowering stakeholders in climate-sensitive urban planning. The platform offers various climate models and visualization capabilities to enhance evidence-based decision-making for urban climate sustainability and resilience. In the future, the platform will expand its offerings, becoming a valuable resource for urban planners, engineers, health practitioners, environmental experts, and residents adapting to a changing climate.


Introduction -Climate Change Projection and Climate Sensitive Planning and Design
The Intergovernmental Panel on Climate Change (IPCC) AR6 climate change 2021 report has clearly indicated that anthropogenic influence has increased greenhouse gas (GHG) emissions, which has been warming the global climate at an unprecedented rate [1].However, according to data from the World Bank, since the first IPCC assessment report in 1990, when we first became aware of the environmental crisis, the annual global GHG emissions, including the GHG emission in Singapore, have not decreased.The climate risks, e.g., heatwaves in cities have been shown to have increased in both frequency and intensity, posing serious threats to human health and the social economy rate [1].
Cities are responsible for more than 60% of the global GHG emissions, and the urban environment is more vulnerable to climate risk than the rural environment due to high-density living and urbanisation [2].Since rapid urbanisation in the mid-1970s, Singapore has warmed notably at a rate of 0.25 degrees Celsius per decade according to the Meteorological Service Singapore.This rate is higher than the global average rate of 0.17 degrees Celsius per decade since 1970, a number based on data from IPCC [3] [1].
If the current urban development approach remains unchanged, local warming will lead to a rise in electricity demand for cooling and the risk that residents will suffer from heat stress.As shown in Figures 1 and 2, the coupling effect of urbanisation and climate change on the future air temperature is expected to be significant [4].

Overarching Research Methods
To mitigate and adapt to future climate risks in the urban environment, both immediate and pre-emptive actions in terms of urban planning and design are urgently needed.However, the impact of climate and relevant research on city and building performance has been very low even though the idea of developing a climate-sensitive method for designing and operating our cities and buildings has been understood for some time.The above issue is caused by the fact that urban planners, architects, meteorologists, and policymakers have been working alone instead of together to address this long-discussed issue as well as the need to balance the human desire for development with the urban carrying capacity.
As architect-environmentalists, my research team at the Urban Climate Design Lab (UCDL), Department of Architecture, National University of Singapore wears the hats of both a designer and urban climate scientist to achieve the above objectives.Our research at UCDL precisely multidisciplinary, crosscutting the fields of architecture design, urban planning, and urban climate science.Our research approaches include Internet of Things (IoT) urban climate sensing, multi-physics numerical simulation, and GIS modelling-mapping, which have been conducted using consistent and unique approaches and aid in a systematic implementation of urban climate information into urban planning and design practice.Our research ambition is to convert this long-discussed research into actionable solutions that mitigate and adapt to potential urban heat risk and other climate issues.

GIS-Based Modelling and Planning Tools
Here, I mainly introduced the development of new GIS climate modelling-planning tools, which are based on urban climate physics and analytics and are developed from urban planning indices such as the site coverage ratio and plot ratio.Therefore, rather than using numerical simulations and wind/water tunnel experiments, urban planners can evaluate the impact of new developments on the microclimate in their planning practice using GIS tools and avoid complicated fluid dynamic calculations [5].Both numerical simulation and wind/water tunnels, especially for modelling work at the urban scale, are timeconsuming, and thus the modelling results from these tools cannot keep pace with the rapid urban planning and design process.As a result, the impact of urban climate technicalities on practical urban planning remains low, and the issues regarding the outdoor thermal environment and air quality have not been addressed in practice despite the growing number of academic journal papers in this field.Using the above as motivation, UCDL research team developed GIS climate modelling-mapping tools based on the analytics of momentum/mass/heat transfer at the urban canopy layer and the urban boundary layer to tackle these challenges, as following.

Urban wind environment model
This GIS-based tool makes wind information more accessible to urban planners and designers, enabling them to readily understand urban permeability for outdoor natural ventilation by calculating the familiar planning index, i.e., ground coverage ratio and frontal area density, rather than performing complicated fluid mechanics calculations.Both the GIS-based tool and the scientific understanding resulting from this study have become an important part of the Sustainable Planning Guidelines in mega cities, e.g., Hong Kong and Wuhan [6] [7].The similar method has been applied in Singapore.As shown in Figure 3, both potential and existing air paths were identified based on the distribution of frontal area density.This modelling and mapping work provide crucial information to support the high-density development at East Singapore [3] Figure 3. Potential and existing air paths identification in the East Singapore [3].

Fine-scale wind environment model
Based on the modelling method introduced in Section 3.1, I developed a novel approach for modeling high-resolution pedestrian-level wind speed with point-based (as opposed to the usual area-based) metrics [8].Modeling high-resolution wind at the pedestrian level in heterogenous urban areas without using Computational Fluid Dynamics (CFD) is extremely challenging but critical to supporting district planning and urban design.The tool, which combines GIS mapping and urban fluid dynamics, can be used in district-scale urban modeling.UCDL research team integrated this modelling tool into the openaccess microclimate digital platform to facilitate the knowledge and technology transfer, as shown in Figure 4.

Urban tree-airflow model
Urban trees and greenery are crucial to the tropical cities, where urban tree and greenery provide significant nature-based cooling effect by shading and evapotranspiration.But at the same time, urban trees could also have negative impact on outdoor natural ventilation.Therefore, it is important to choose the appropriate planting locations and tree species and modelling work is needed to support this decision-making.However, it is usually very expensive to apply numerical simulation to estimate the drag force of trees on air flow.
This GIS-based tool estimates the impact of urban trees on airflow based on the balance between the total drag force of both buildings and trees on the airflow and vertical flux of horizontal momentum [9].This modelling tool correlates tree geometries with wind speed in the street canyon, thereby enabling landscape planners to make crucial evidence-based decisions regarding tree species and planting locations using their in-house data.With such a new and innovative practical tool, landscape planning can introduce more trees into urban areas and meanwhile, minimize the negative effects of trees on the outdoor natural ventilation.

Anthropogenic heat dispersion model
Our research on anthropogenic heat dispersion was supported by Singapore National Research Foundation.Anthropogenic heat is an important factor for street air warming, especially in residential areas and at night.Therefore, it is important in terms of public health and energy consumption for cooling.Compared with air flow and pollutant dispersion, the challenge of heat dispersion modelling is the buoyancy effect.UCDL research team developed an innovative analytical method for including the buoyancy effect into the modelling by introducing a buoyancy coefficient that is estimated based on advanced CFD simulation results.Using the buoyancy coefficient, a GIS-based tool was developed to estimate the impact of anthropogenic heat on air temperature.With this GIS tool, both the transient and time-averaged air temperature increment can be easily modelled at the urban scale, e.g., the entirety of Singapore, as shown in Figure 6.

Envisaged Users
First, academics and students can leverage the GIS-based modelling tool as a valuable teaching/learning tool across various disciplines, including architecture, the built environment, urban planning, and climatology by proficiently interpreting and visualizing urban climate modelling results.Moreover, the application in architectural education extends beyond theoretical modules, serving as a design tool in design studios within the School/Department of Architecture.Currently, Year 3 and Year 5 architectural students at NUS have been using microclimate digital platform in their studio projects.Secondly, similar to architectural academics and students, practicing architects and urban planners can seamlessly incorporate microclimate consideration into urban design and architectural design, especially at the early stage, using GIS-based modelling tools.
Thirdly, the public is encouraged to cultivate awareness of environment issues and embrace sustainable practices with the assistance of the GIS-based modelling tools, which helps the public access the urban microclimate information.
Additionally, government agencies, specializing in policy making and implementation, stand to benefit significantly from GIS-based modelling tools.Armed with better understandings and insights, along with straightforward interpretation and visualization, these agencies can make well-informed decisions and engage in effective communication with diverse array of stakeholders, ensuring a more comprehensive and inclusive approach.
Last but not least, other stakeholders, e.g., property agencies, can capitalize on the GIS-based modelling tools to access the microclimate information and strategically utilize the information to persuade prospective house and apartment buyers, offering a unique climate-related selling point.

Conclusions and Future Studies
The GIS modelling-mapping tools introduced in this paper have drawn attention to the rising importance of systematic climate sensitive planning tools/guidelines and platforms.First, the above-mentioned models have been applied in several key policy-level research & design projects commissioned by the Hong Kong, Wuhan, Macau, and Singapore governments.Second, the above-mentioned models have been integrated into an open-access digital platform, UCDL Microclimate Digital Platform, to facilitate the knowledge and technology transfer.
We have been developing an open-access Microclimate Digital Platform (MDP) to support climate sensitive urban planning/design practices and training, and promote climate situation awareness and research collaboration (data, models, design, etc., sharing and exchange).The primary goals of this platform are to facilitate knowledge and technology transfer and empower stakeholders to make evidence-based decisions to build up urban climate sustainability and resilience.MDP is the first platform to integrate multi-scale-physics climate modelling and visualization through a set of GIS-based modelling tools and a digital platform.This integration will enable stakeholders, such as urban planners, engineers, health practitioners, environmental engineers, and residents, to easily obtain climate information, especially regarding the coupling impacts of climate change and urbanization on urban climate.We aim to include more climate models into MDP in the future.

Figure 1 .
Figure 1.Projection of the future local impact of climate change on air temperature in Singapore [4].

Figure 2 .
Figure 2. Impact of future urbanization on air temperature in Singapore [4].

Figure 5 .Figure 6 .
Figure 5. Modelling of the drag force of urban trees on air flow, and suggestions on tree species to minimize the negative effect of trees on air flow [9]