Journal Article

Probabilistic Models Significantly Reduce Uncertainty in Hurricane Harvey Pluvial Flood Loss Estimates

Sairam, Nivedita, Merz, Bruno, Rözer, Viktor, Schröter, Kai, Müller, Meike, Doss‐Gollin, James, Kreibich, Heidi, Lall, Upmanu

2019

Overview

Pluvial flood risk is mostly excluded in urban flood risk assessment. However, the risk of pluvial flooding is a growing challenge with a projected increase of extreme rainstorms compounding with an ongoing global urbanization. Considered as a flood type with minimal impacts when rainfall rates exceed the capacity of urban drainage systems, the aftermath of rainfall‐triggered flooding during Hurricane Harvey and other events show the urgent need to assess the risk of pluvial flooding. Due to the local extent and small‐scale variations, the quantification of pluvial flood risk requires risk assessments on high spatial resolutions. While flood hazard and exposure information is becoming increasingly accurate, the estimation of losses is still a poorly understood component of pluvial flood risk quantification. We use a new probabilistic multivariable modeling approach to estimate pluvial flood losses of individual buildings, explicitly accounting for the associated uncertainties. Except for the water depth as the common most important predictor, we identified the drivers for having loss or not and for the degree of loss to be different. Applying this approach to estimate and validate building structure losses during Hurricane Harvey using a property level data set, we find that the reliability and dispersion of predictive loss distributions vary widely depending on the model and aggregation level of property level loss estimates. Our results show that the use of multivariable zero‐inflated beta models reduce the 90% prediction intervalsfor Hurricane Harvey building structure loss estimates on average by 78% (totalling U.S. $3.8 billion) compared to commonly used models. Key Points Recent severe pluvial flood events highlight the need to integrate pluvial flooding in urban flood risk assessment Probabilistic models provide reliable estimation of pluvial flood loss across spatial scales Beta distribution model reduces the 90% prediction interval for Hurricane Harvey building loss by U.S.$ 3.8 billion or 78%

• Publisher: John Wiley & Sons, Inc
• Subject: Accounting / Adaptation / climate change adaptation / Data collection / Datasets / Decision making / Drainage systems / Environmental risk / Estimates / Extreme weather / Flood damage / Flood hazards / Flood risk / Flooding / Floods / Hurricane Harvey / Hurricanes / loss modeling / Mathematical models / pluvial flooding / Predictions / probabilistic / Probabilistic models / Rain / Rainfall / Rainfall rate / Rainstorms / Risk assessment / Storm damage / Uncertainty / Urban drainage / Urban drainage systems / urban flooding / Urbanization / Water depth