**4. Conclusions**

Due to the increase of impermeable areas and the consequent increase of floods in urban areas, the inadequacy of traditional urban drainage systems is increasingly notable. The trend is that the flood events and other problems related to the recharge and pollution of water resources will grow in the coming years due to global warming and man-made changes. In this way, the importance of using new sustainable drainage systems increases in order to enhance the permeability of surfaces and restore the natural hydrological cycle. These systems include permeable pavements, which were the focus of this paper.

The literature reviewed shows that permeable pavements are capable of filtering and storing stormwater. When compared to the traditional drainage system, they are sustainable and cost efficient, being fully adequate for urban areas, bringing benefits such as reducing stormwater runoff, as well as improving the quality of water infiltrated through the pavement. The LCA studies reviewed were able to provide an estimate of the sustainability of permeable pavements. However, there is still a need for a methodology capable of providing more precise results regarding the environmental impacts caused by these pavements. Thus, the evaluation should not be linked only to environmental benefits related to their lifespan, but assessments are necessary in the steps that precede and follow the lifespan.

Various parameters, such as local weather patterns, regulatory requirements, infiltrated stormwater quality, lifespan and treatment efficiency of systems, should be taken into account. The phases of goal and scope, inventory analysis, impact assessment and interpretation should be more homogeneous, defining phases and processes of the evaluation and the minimum amount of data to be considered in the modelling of LCA. Thus, heterogeneity in the functional units and other components should be avoided, bringing more consistent results and leading to a real evaluation of the environmental impacts caused by permeable pavements.

Although life cycle studies on permeable pavements still present several immature concepts, being only in their early stages, LCA is essential to guide planning and decision-making, leading to systems that consider the increase of water resources and the reduction of natural disasters and environmental impacts.

**Author Contributions:** L.N.A. wrote the first draft of the article; L.P.T. and E.G., contributed ideas concerning the structure and content of the article, and wrote the final version.

**Funding:** This research did not receive any specific gran<sup>t</sup> from funding agencies in the public, commercial, or not-for-profit sectors.

**Conflicts of Interest:** The authors declare no conflict of interest.
