Predicting Tree Effects on Urban Microclimate of Megacity Dhaka: Considering the 2022 building construction regulation changes

Megacities like Dhaka are facing unprecedented challenges due to the rapid expansion of their populations, resulting in a severe shortage of habitable space. To accommodate this burgeoning population, construction activities often encroach upon urban vegetation and natural landscapes, leading to their rapid degradation and destruction. The consequences of this loss of greenery are far-reaching, impacting the local microclimate in many ways. Urban vegetation, including trees, shrubs, and green spaces, serves as a crucial natural regulator of the climate within cities. These elements play a pivotal role in moderating air temperature, humidity levels, air quality, and overall comfort for residents. However, the exceptional pace of urbanisation in Dhaka has led to a staggering loss of green spaces over the years. For instance, between 1989 and 2020, Dhaka witnessed a staggering 56% reduction in its greenspace, leaving only a mere 2% of healthy vegetation. This alarming trend is primarily attributed to unplanned urbanisation practices that prioritise construction over environmental preservation. In response to the escalating challenges posed by unplanned urbanisation, the government of Bangladesh has introduced a series of building regulations over the years. However, these regulations, such as the Building Construction Rules of 1996, 2008, and 2022, were primarily focused on controlling the haphazard construction of buildings without adequately considering their environmental implications. Particularly, the focus on compact, high-density building structures to accommodate population growth has worsened the urban heat island (UHI) effect. To address these issues, the government has progressively upgraded its building regulations, introducing concepts like Floor Area Ratio (FAR) and location-based FAR in 2008 and 2022, respectively. These regulatory measures aim to create a balance between urban development and environmental sustainability by ensuring the preservation of green spaces while accommodating population growth. However, the efficacy of these regulations in mitigating the adverse effects on the microclimate remains uncertain. This study aims to comprehensively evaluate the impact of these building regulations on Dhaka's microclimate as a response to the above challenges. It employs advanced methodologies, including GIS-based data, 3D modeling, microclimate measurements, and simulation using the ENVI-met model. By comparing different scenarios based on varying building regulations, the study aims to provide valuable insights for urban planners and policymakers to formulate sustainable building policies that prioritise green and open spaces and improve the city's microclimate, ultimately contributing to the development of more liveable and resilient urban areas.