3D GIS Modelling of Road and Building Material Stocks: A Case Study of Grenada

Recent years have witnessed significant material stock accumulation within built environments, resulting in substantial environmental issues, such as greenhouse gas emissions, toxic or harmful wastes, resource scarcity, and land use conflicts. Quantitative analysis of in-use material stocks is important for assessing resource appropriation, improving the socio-economic metabolism model, and enhancing adaptive capacity to climate change. This research presents a bottom-up GIS spatial approach for modelling in-use road and building material stocks in Grenada, a small island state. LiDAR data were applied to the estimation of building heights and building stocks to improve current material stock accounting approaches. A 3D web-based application was developed to visualize material stocks in 3D building models and to enhance the understanding of the spatial distribution of material stocks. In addition, a comparative review was conducted to compare the methodological approach, results, and conclusions of this study with previous material stock studies in Grenada. Results of this study indicate that in 2015, 4,375 kilo tonnes (40.96 t/capita) of materials were stocked within Grenada road networks, which were about one-third of that accumulated in buildings and accounted for a large share (24%) of total material stocks. Aggregates stocked within road networks occupied the largest proportion of stocks, contributing to 55% of total aggregate stocks. The considerable amount of road stocks supports the important role of materials stocked in non-building infrastructure in the context of small island states. A large proportion of road stocks were accumulated in the low-lying coastal areas, which are highly vulnerable to sea level rise. It is predicted that a sea level rise of 2.0 m would cause the majority of road stocks (over 18,187 tonnes) along the coastline of St. George’s Harbour to be inundated. In terms of building material stocks, this study combined GIS footprint data with LiDAR elevation data to obtain the building height for each building, finding that compared with height assumptions based on occupancy classes, LiDAR-derived height estimates were closer to ground truth heights and could better represent the heterogeneity among buildings. The study for the sample site of Grenada (St. George’s) demonstrates that using the inaccurate class-based height assumptions resulted in about 4.8% of overestimation in building stock estimates compared to using LiDAR-derived heights. The most discrepancy was found in concrete since concrete is the main material used in building construction. 3D building models in CityGML format and a 3D WebGIS application built on top of ArcGIS API for JavaScript were developed for Grenada integrating material stocks with the 3D city model. These 3D products can provide policy makers and practitioners with a new perspective and additional insights into material stocks and enable the public to access proprietary GIS data and material stock information through a user-friendly interface. This research serves as a pilot for assessing a novel methodology for estimating building and non-building material stocks in the context of small island states. The methodological approaches and results detailed in this research can further aid small island states in better assessing resource appropriation and evaluating their adaptive capacity to climate change.

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