Land use/cover change and its implications on carbon stocks in the urban green spaces of Mbarara city

Abstract

Urban land use/cover change-driven effects on carbon stocks and emissions have become a critical concern for the attainment of sustainable urban development. Yet, the historical, current and future land use/cover changes and subsequent impact on carbon stocks in urban green spaces have not been well documented in the rapidly expanding cities in Sub-Saharan Africa. This study aimed to investigate the spatial-temporal land use/cover change and its impact on carbon stocks in urban green spaces in Mbarara city by; (i) examining the spatial-temporal changes in LULC between 2013 and 2023; (ii) quantifying current and historical carbon stocks in the different green spaces; and (iii) predicting LULCC and carbon stocks for 2043. To examine the LULCC, the study used satellite data from the USGS Earth Explorer for the series 2013, 2018 and 2023. Iso-Cluster and Maximum likelihood classification were used for image analysis in ArcGIS 10.8 version, and six LULC classes were identified; built-up areas, bushland, cropland, grassland, tree plantations and wetland. To determine the AGC, field measurements of tree DBH and height were taken and a destructive approach was used for the grass and herbaceous vegetation. Samples were taken to the laboratory for carbon content analysis. In addition, the LULC for 2043 was predicted using the CA-Markov model and future carbon stocks were computed following the IPCC guidelines. The findings revealed that built-up areas and tree plantations steadily increased in spatial extent by 11.8% and 0.3 % respectively while grassland, cropland, bushland and wetland decreased by 6.9, 4.2, 0.8 and 0.3% respectively by 2023. In addition, the built-up areas experienced the highest net gain while grassland experienced the highest net loss. Still, the total aboveground carbon stocks in green spaces were 73.40, 72.27 and 75.44 Gg for 2013, 2018 and 2023 respectively, the increase largely driven by an increase in the area under tree plantations. This study predicted LULCC, which shows, that by 2043, built-up area will cover 49.5% (21,1830 ha). As compared to the year 2023, built-up will increase by 33.9% while the area under grassland, bushland, cropland tree plantations and wetland will decline by 21.9, 7.7, 1.0, 1.4 and 1.9 % respectively. Consequently, the predicted LULCC are expected to cause a reduction in AGC storage of 38.55 Gg by 2043 resulting from the decrease in green spaces, especially tree plantations and grassland. It is evident that the explosion of built-up areas will persist at the expense of green spaces negatively affecting carbon storage. This highlights the need by city management to prioritize ecological protection and increase tree planting along all roads and public spaces to enhance carbon storage.