NH33A-03 Quantifying Hidden Hazards: A Flood Risk Assessment Framework for Urban Underground Spaces Under a Changing Climate

Traditional urban flood risk methods overlook the complexities of runoff in urban landscapes and lack the spatial and temporal resolution necessary to fully capture the risks posed by the resulting flooding.

These limitations are especially critical when considering the impacts of flooding on underground spaces. This study introduces a novel flood risk assessment framework that explicitly integrates underground urban spaces such as basements, tunnels, and underground garages, into a high-resolution Rain-On-Mesh (ROM) hydrodynamic model.

The methodology is demonstrated through case study eastern Cambridge, MA, with a focused analysis on the 168 acres of the MIT campus. The main campus has 33 buildings with interconnected basements and over 1,000 identified water entry points. The study compared a traditional surface model with the MIT combined surface/basements hydrodynamic model. The results highlight the critical role of underground infrastructure in shaping urban surface flood dynamics as well as the risk to underground assets. For example, certain surface flood inundation zones adjacent to the campus area vanish due to basement flood inflows, while new basement flooding emerges in buildings not adjacent surface flooding. With direct simulation of extent and depth of flood water in the basement, a new depth-damage approach was developed employing the geospatial database of MIT assets. The combination of modeling the basement flooding and the improved damage assessment resulted in reducing the estimate of the damage to the MIT Campus for the the current 100-year 24 hour storm by a factor of six compared to a surface flood model highlighting the limitations of conventional surface-based flood damage assessments.

Under a projected climate change storm scenarios for 2070, the analysis shows that both the extent and severity of flooding increase substantially compared to present-day conditions, highlighting the amplified risks associated with climate change.