Methodology

Methodology Sydney's central business district (CBD) is chosen as a case study (33°52′5″S 151°12′44″E, 58 meters above sea level). The figure 6 depicts the urban region that is considered in the analysis.

Figure 6: Maps showing the selected site for the study

The simulations discussed in the following section are the result of the different proposals for the mitigation strategies for Sydney CBD area. The goal of the project is to minimize the impact of UHI with incorporating solar power generation in Central Business District of Sydney during extended heat periods. Due to global warming such summerly heat waves are expected to occur more often and be longer lasting in the future (Jacob et al., 2008). The study focused on the selected area in Sydney City, that is known for its relatively warm climate.

ENVI-met has been utilized and evaluated to see how different urban design alternatives affect the outdoors' thermal environment. With a common grid resolution ranging from 0.5 to 10 meters, it's a three-dimensional non-hydrostatic local meteorological system used to simulate weather parameters in urban environments. There is a complete radiation budget considered by the model (i.e., reflected and diffused solar radiation, direct radiation, and long-wave radiation). It uses flow behavior and thermodynamics to simulate how meteorological variables change during the day. Vegetation, Buildings, surface properties, soils, and meteorological contour conditions all play a role in the ENVI-met model's

simulation of the atmosphere's current state (Bruse and Fleer,1998). The thermal inertia of the walls and roof is also accounted for by the building module.

There are several different parameters which go into ENVI-met calculations which include meteorological data as well as soil surface and temperature profiles. Wind and cloudiness remain constant, which has an impact on the model's ability to produce findings that are representative when compared to hourly measurements.

The simulations performed with ENVI-met within the scope of this project with the goal to identify the influence of certain typical urban structures on the urban microclimate and to develop possible strategies to mitigate heat stress within these structures. As ENVI-met is not capable of simulating a whole city but rather single urban quarter, such urban quarter is selected for the simulation. This quarter represent different types of urban commercial areas, heritage buildings and offices, restaurants, high-density housing constructions, and old structures adapted to residential or commercial uses characterize the regions that are thought to be typical for central Australian cities. The microclimate of the model areas is then simulated with the boundary conditions of an extreme heat scenario which will consequently be referred to as worst case scenario: a summer day at the end of a longer lasting heat period with a maximum air temperature of over 35◦C and a maximum solar irradiation. Simulation is performed for the month of January by considering the average extreme heat temperature, date, and time, i.e., 15 January 2020 (2 PM).

Layout plans, satellite photos, and other information found on the internet are used to make the model areas. Building shapes and heights are defined by the layout blueprints (Google Maps n.d.). The layout blueprints for these buildings were largely old, thus newer ones are developed only from aerial views and photos available using current information. These images were also employed in the modelling of the area's ground surface and vegetation.

As a result of the relatively inaccuracy of this digitalization approach, the errors made are estimated to be less than two meters in length. The model grid's vertical and horizontal resolutions are determined by the constraint on the model's size. The selected area's 3D model in ENVI-met (a portion of the district) is shown in the figure 7. With frequent and average wind flow, the buildings are positioned at various levels of height. The spacing between the structures varies from 10 meters to more than 10 meters. The measurements of air temperature taken during Sydney's January 2020 heat wave, which was

Figure 7: Site selected for the study at Central Business District of Sydney, NSW,

Australia