Multiple levels of human instability due to urban overland flow within the 21st century: An urban Catchment study case in Brazil

Extreme rainfall events in urban environments are a well-known issue in society due to the multiple impacts that can induce, which are expected to increase due to climate change effects. During high intensity rainfall events, an often overlooked risk is the threat to pedestrian stability posed by overland flow forces that can induce instability when crossing the streets. To analyze this gap, we employ hydrodynamic modeling in a catchment in São Paulo city, Brazil, under climate change conditions to assess human instability with multiple levels of vulnerability, according to the age, gender, weight and height of the people. Our results allowed us to identify zones with potential risk that tend to increase along the 21st century, where children are the most significant vulnerability group to potential injuries compared to adults. We observed that human instability is more sensitive to pulses of rainfall intensity than to the total rainfall volume, indicating that even low volume rainfall events can pose a considerable danger to pedestrians. The Results provide valuable insights to decision-makers for better urban planning against challenges exacerbated by climate change in the future. This research, as the first of its kind, helps to identify risk zones for the implementation of measures to reduce both flow depth and velocity. In addition, this study offers a potential tool for enhancing communication and knowledge sharing with society, aiming to influence the perception of this type of risk, which is often underestimated, especially by pedestrians, in order to help prevent injuries or potential fatalities. • Low volume rainfall events may pose a significant hazard to pedestrians in the 21st century. • Human instability correlates more with rainfall intensity than total rainfall volume. • Children are more vulnerable than adults to human instability. • Exposure may spread to new areas due to climate change increasing overland flow. • Risk may worsen in current areas, affecting adults as well as children.