Enhancing megacities' resilience to flood hazard through peri-urban nature-based solutions: Evidence from Mexico City

Floods are one of the most frequent natural hazards in almost every country, with climate change exacerbating their frequency and intensity. Nature-based solutions (NbS) can be a cost-effective way to make human settlements more resilient to flooding. However, decision-makers need reliable information on which to base NbS policy and funding. This research estimates the potential of peri-urban NbS to regulate water flow and the benefits downstream through the development of supply and demand indicators for the context of complex megacities. In our Mexico City case study the supply indicator is the runoff coefficient, which is spatially estimated across peri-urban areas, and the economic value is estimated using replacement cost (grey infrastructure). The demand indicator identifies flood-prone areas based on spatially explicit ponding events and avoided costs of insurance flood claims data and estimates with parametric cost functions. The supply indicator provides straightforward information for decision-makers to spatially target conservation in peri-urban areas where runoff coefficients are high combined with flood-prone areas, while the lowest coefficients reinforce the importance of policies for protected areas. In combination with demand indicator information, we find NbS in peri-urban upstream catchments is cost-effective compared to avoidable flood-related costs and alternative investments in grey infrastructure.