The potential insitu and downwind thermal conditions of a new coastal city built on reclaimed land in Lagos, Nigeria

Due to the ongoing rapid urbanization, built-up landcover has geometrically increased in many global cities in recent years. Specifically, many coastal cities are almost using up their landed area, thus, land reclamation is increasingly becoming popular as a solution for further urban and economic development to cater for the growing population. However, such landcover changes could significantly impact the existing environmental condition and should be investigated.  One such case is the ongoing massive development of an expanse of reclaimed land on the Atlantic coast of Lagos, Nigeria. Thus, this study investigates the potential micro-climatic impact of the conversion of the large ocean surface to a built-up area, locally in the new development and downwind in the existing neighbourhood. To achieve this, we applied the ENVI-met micro-climate model in which a parametric study were conducted. Four scenarios i.e. the pre-reclamation - “reference” case, and three post-reclamation - “highly densified”, “grey design” and “grey-green design” scenarios were evaluated for their micro-climate and thermal comfort situations. Analyses involve the comparison between the pre-and post-reclamation scenarios, and inter-scenario comparison to reveal the influence of urban structure and design decisions on insitu and downwind thermal conditions. The result revealed both the insitu and downwind areas became warmer both at day and night-time due to significant (about 50%) landcover change from water to paved built-up surface. Although the imposed high-rise development on the reclaimed area has an impact on the ventilation flow pattern and magnitude, the relatively warmer air generated in the newly built area is still advected into the existing neighbourhood areas downwind.  However, depending on the urban structure/layout and design features imposed on the reclaimed area, the intensity of the consequent daytime and night-time warmth and thermal discomfort varies across the study domain. The warming intensity is stronger during daytime than nighttime and highest with the high densified/grey-design and otherwise with the green-grey design indicating the role of greening as a key climate-resilient strategy. Similarly, the green-grey design scenario improved the daytime thermal comfort condition significantly compared to the highly densified and grey design counterparts. However, at night-time, the downward longwave radiation from the trees made the environment warmer but this effect is significantly outweighed by the positive effect observed during the daytime. Finally, this study gave insights to developers, urban planners, architects, and decision-makers on the need to mitigate the potential environmental impacts of such large-scale land cover change and development.