Assessment of urban flood vulnerability to climate extremes

Authors

Heejun Chang - Portland State University, SeongYun Cho - Portland State University, Lumas Helaire - Portland State University, Stephen Talke - Portland State University

Body

Urban areas are particularly vulnerable to floods resulting from weather and climate extremes. Warm air temperatures induced by anthropogenic climate change are likely to increase rainfall intensity and sea levels. All these factors influence flood vulnerability on the tidally-influenced lower Willamette River in Oregon, USA. To address the potential combined impacts of rising sea levels and water levels in urban flood, we created synthetic flow and sea level rise scenarios from the most recent extreme flood event, in collaboration with the City of Portland practitioners and interdisciplinary scientists. Additionally, we conducted a practitioner survey to identify relevant indicators to assess urban flood vulnerability. A numerical hydraulic model was calibrated against representative historical flood events. The models were then simulated to show the effect of an up-to 10% increase in flow and an up to 1.5m increase in sea-level. Results suggest that flood vulnerability is most sensitive to changing flow rather than sea level rise, primarily because increasing sea-level reduces the river slope out of the ocean. However, different reaches exhibit different social and biophysical vulnerability under different scenarios. Our community engaged approach to urban flood vulnerability offers decision-relevant information to city managers who seek to make flood resilient city to climate extremes.
Keywords:urban flood, climate extremes, modeling, vulnerability, co-production of knowledge

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