A bottom-up building stock quantification methodology for construction minerals using Earth Observation. The case of Hanoi

Increasing demand for significant volumes of construction materials, especially sand for use in concrete, in rapidly developing urban environments is becoming a significant socio-economic and environmental issue. The consumption of concrete (comprised of sand, aggregates and cement) is especially concerning on a city level as vast volumes of materials are extracted within the urban hinterland, causing direct impacts locally and the potential for supply issues directly impacting city level metabolism. Excessive consumption and poor management of these materials make it increasingly hard for society to ensure new urban development and infrastructure projects, essential for maintaining the health of cities, meet sustainable development objectives. However, it is difficult to implement suitable resource management policies without first understanding how materials are produced and consumed at an appropriate spatial level. For many areas, especially on a city level, such data is absent, especially so for sand and aggregates which can further exacerbate these local supply issues and environmental impacts. This study attempts to address this data gap via combining earth observation datasets with estimates of materials contained within urban infrastructure (material intensities) to calculate the rapid increase of construction material stocks in Hanoi. Spatial data on buildings have been gathered using, producing, and collating a variety of spaceborne open-source datasets on built up areas (GlobalMLBuildingFootpint, World Settlement Footprint 3D, Open Street Map) and land use classification maps. Linking this spatial data with estimated quantities of sand, gravel, cement and concrete in typical buildings in Hanoi enables quantification of building stocks for a range of building types over a time series. The results show that for every new km2 of urban infrastructure approximately 520,000 tonnes of concrete, or 360,000 tonnes of sand, 580,000 tonnes of gravel and 115,000 tonnes of cement are required. If the Hanoi Masterplan is to be achieved by 2030, then the material demand is likely to be for 106 million tonnes of concrete or 73 million tonnes of sand, 118 million tonnes of gravel and 24 million tonnes of cement. These all exceed historical consumption trends and are far in excess of current extraction rates and therefore careful planning is required to ensure access to sustainable resources into the future.