Going beyond the flood insurance rate map: insights from flood hazard map co-production

Adam Luke,Richard A Matthew,Kristen A Goodrich,David L Feldman,Victoria Basolo,Amir Aghakouchak,Jochen E Schubert,Ana Eguiarte,Abigail Reyes,Danielle Boudreau,Kimberly Serrano,Brett F Sanders

doi:10.5194/nhess-18-1097-2018

Abstract

Abstract. Flood hazard mapping in the United States (US) is deeply tied to the National Flood Insurance Program (NFIP). Consequently, publicly available flood maps provide essential information for insurance purposes, but they do not necessarily provide relevant information for non-insurance aspects of flood risk management (FRM) such as public education and emergency planning. Recent calls for flood hazard maps that support a wider variety of FRM tasks highlight the need to deepen our understanding about the factors that make flood maps useful and understandable for local end users. In this study, social scientists and engineers explore opportunities for improving the utility and relevance of flood hazard maps through the co-production of maps responsive to end users' FRM needs. Specifically, two-dimensional flood modeling produced a set of baseline hazard maps for stakeholders of the Tijuana River valley, US, and Los Laureles Canyon in Tijuana, Mexico. Focus groups with natural resource managers, city planners, emergency managers, academia, non-profit, and community leaders refined the baseline hazard maps by triggering additional modeling scenarios and map revisions. Several important end user preferences emerged, such as (1) legends that frame flood intensity both qualitatively and quantitatively, and (2) flood scenario descriptions that report flood magnitude in terms of rainfall, streamflow, and its relation to an historic event. Regarding desired hazard map content, end users' requests revealed general consistency with mapping needs reported in European studies and guidelines published in Australia. However, requested map content that is not commonly produced included (1) standing water depths following the flood, (2) the erosive potential of flowing water, and (3) pluvial flood hazards, or flooding caused directly by rainfall. We conclude that the relevance and utility of commonly produced flood hazard maps can be most improved by illustrating pluvial flood hazards and by using concrete reference points to describe flooding scenarios rather than exceedance probabilities or frequencies.

Highlights

Management of flooding is a major societal challenge that is only expected to worsen due to several trends including population growth and urbanization (Sundermann et al, 2014), sea level rise (Hallegatte et al, 2013), intensification of precipitation extremes (Lenderink and Van Meijgaard, 2008; Coumou and Rahmstorf, 2012), and the compounding effects of sea level rise and terrestrial flooding (Moftakhari et al, 2017)
The requested revisions generally fell into three categories: requests for the hydrologic/meteorologic conditions of the mapped hazard, further clarification of the map legends, or requests for additional geospatial data to be shown on the map
The amount and duration of precipitation leading to the mapped hazard was often requested for both sites, while Tijuana River valley (TRV) end users requested the flow rate of the Tijuana River associated with the hazard maps

Summary

Introduction

Management of flooding is a major societal challenge that is only expected to worsen due to several trends including population growth and urbanization (Sundermann et al, 2014), sea level rise (Hallegatte et al, 2013), intensification of precipitation extremes (Lenderink and Van Meijgaard, 2008; Coumou and Rahmstorf, 2012), and the compounding effects of sea level rise and terrestrial flooding (Moftakhari et al, 2017). Insured losses from natural disasters have increased globally (Munich Re, 2005), and while the causes of growing losses are complex and debatable, the increasing exposure and value of capital at risk has undoubtedly played a major role (Bouwer, 2011). Losses from floods and hurricanes in the (US) have tripled over the past 50 years (Gall et al, 2011), and the National Flood Insurance Program (NFIP) is operating at a deficit of about USD 1 billion annually with a debt of over USD 20 billion owed to the US treasury before considering insured losses from the 2017 hurricane season (Pasterick, 1998; Brown, 2016). Properties insured by the NFIP represent the second largest liability of the US federal government after the Social Security program (Gall et al, 2011)

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