One of the drawbacks of an MFA is the inability to quantify the environmental impacts of the urban resource flows. By combining MFA and LCA approaches, it becomes possible to better understand various environmental impacts for each type of material flow. There is no single methodological framework that describes this hybrid method. Instead, a number of different approaches have been implemented. The MFA that precedes the LCA could be based on the Brunner and Rechberger approach (García-Guaita et al. 2018), or it could follow the UMAn model (Westin et al. 2019), for instance. The challenge within this method is that generally high-level material flow data obtained from an MFA are not compatible with product-specific required input into an LCA. To overcome this issue, various approaches exist. One option is to limit the scope of the MFA on the most relevant flows, rather than undertaking an EW-MFA (for instance, (García-Guaita et al. 2018) focus on seven material flows in Santiago de Compostela). Another option is to select a few representative products for each category (Westin et al. 2019).

Independently from the chosen strategy, this approach inherently relies on a large number of assumptions and generalisations, as product-based breakdowns are unattainable for entire sectors or material groups, let alone cities. A degree of uncertainty is therefore necessarily introduced to the LCA results. However, exact precision is not necessarily required to identify hotspots. This hybrid method does allow for an understanding of impacts on a number of environmental impact categories and provide new insights that can be actionable and useful in policy (Westin et al. 2019).

Aliases: this method is sometimes referred to as UM-LCA (e.g. (González‐García and Dias 2019)).