Estimating The Cooling Potential of Urban Green Spaces in Mitigating Urban Heat in The City of Accra

Abstract

The tropical region of Africa is noted for high temperatures which has implications for comfortable and quality life with consequential impact on human health. Urban green spaces (UGB) are efficient in mitigating urban heat but a compassing study to understand the role of vegetation in reducing Land Surface Temperatures (LST) in the city of Accra is lacking. This research estimates how much greenness can be utilized to reduce LST and prevent rising urban heat island (UHI) effect. This study is based on both spatial, temporal and statistical analysis of LST and NDVI. Spatial analysis of UHI revealed high LST in the coastal areas and lower LST in areas up north where vegetation cover is high. Across the 25-year period (2021 to 2024) LST showed an increasing trend and NDVI an inverse trend by employing Mann-Kendall Analysis. For the year 2015, 2021 and 2024 mean LST observed were 30.51°C, 35.60°C and 34.92°C respectively. Similarly, spatial results showed an equally spreading trend of LST values in major towns and cities, emphasizing the need for urban greening to reverse the trend. Peri-urban towns such as Dodowa and Big Ada showed lower LST compared to highly urbanised areas such as Nungua, La and Adabraka. Well planned areas such as Tema, Legon and East Legon showed moderate to low LST values. Trees had the highest NDVI and the lowest LST while built-up areas conversely showed the lowest NDVI and high LST respectively. Vegetated and non vegetated areas showed a varied range of LST, with Mean LST in non-vegetation area being 37.30°C and vegetation 33.32°C, further bolstering the role of greens in reducing high temperatures. Using a simple regression model, a moderate but strong inverse relationship between LST and NDVI was observed, using 2021 data. The equation showed a Coefficient of Determination (R²) of 0.57. The result suggests a strong influence of vegetation cover on LST, underscoring the need for afforestation, green roofing and urban parks in the region. Upon analysing the cooling potential of five urban green spaces, it was observed that two out of five have significant cooling potential. Legon Botanical Garden performed with a cooling potential of 4.1°C at 550m, followed by Achimota Forest at 3.3°C at the same distance. The weakest performer was the Efua Sutherland Childrens’ Park due to its small size and the presence of a highly built surrounding. Scenario analysis revealed that converting 80% of grassland into areas with a minimum NDVI of 0.27 could result in at least a 1°C decrease in land surface temperature, based on 2021 Landsat data. It is therefore important that green spaces are maximisation in urban development.