Understanding Inland Flood Risk
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The document discusses inland flood risk and challenges in managing it. It presents a framework for understanding inland flood risk that begins with precipitation data and models how precipitation leads to flooding through hydrological processes. The framework accounts for various factors that influence flood severity such as defenses, drainage, and changing land use. Developing a comprehensive modeling approach based on this framework allows for a true understanding of inland flood risk.
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Understanding Inland Flood Risk
- 1. 1Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 RISK ON THE RISE: MANAGING INLAND FLOOD RISK Dr. Christine Ziehmann Model Product Management Dr. Arno Hilberts Model Development Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015
- 2. 2Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 MEET THE EXPERTS Dr. Christine Ziehmann Vice President, Model Product Management Dr. Arno Hilberts Senior Director, Model Development
- 3. 3Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 HOW DO YOU DEFINE INLAND FLOOD? Surface Water Flooding 2012 UK Flood Sequence Riverine Flooding 2013 Central Europe US$1.8 B 486 K CLAIMS US$4.2 B 7 COUNTRIES
- 4. 4Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 HOW DO YOU DEFINE INLAND FLOOD? Flash Flooding 2014 Midwest Flash Flood, USA US$1.8 B 75 K IMPACTED Second-highest 24-hour rainfall Detroit, MI USA 2014 116 mm
- 5. 5Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 US$9 B 41 FATALITIES HOW DO YOU DEFINE INLAND FLOOD? Tropical Storm-Induced Flooding Tropical Storm Allison, Houston TX USA ~ week ~1,000 mm
- 6. 6Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 >US$45 B >6 MONTHS IN PLACES HOW DO YOU DEFINE INLAND FLOOD? Monsoon Flooding 2011 Thailand Foods >13 M AFFECTED 815 FATALITIES
- 7. 7Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 MANY WAYS TO THINK ABOUT INLAND FLOOD… >US$45 B Economic Loss ~33% Insured ~US$9 B Economic Loss ~55% Insured ~US$1.8 B Economic Loss ~28% Insured >US$2.5 B Economic Loss ~60% Insured ~US$16.8 B Economic Loss ~25% Insured The cost to the industry varies considerably
- 8. 8Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DIFFERENCES IN GLOBAL FLOOD RISK MANAGEMENT HAZARD POOLS HIGH COVERAGE LOW COVERAGE NFIP Flood Re NCIF 50 - 60% 40 - 70% up to 75% BR, EC, MX CN, PH, TW AT, DE, IT, TR
- 9. 9Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 PAST CHALLENGES TO PROFITABILITY § US GOVERNMENT POOL CASE STUDY: NFIP – Run at a loss four out of past 10 years – 2005: losses were 900% of premium – Peak losses were coastal, but inland has attritional impact § INSURANCE INDUSTRY CASE STUDY: U.K. – Significant loss history: 2013-14, 2012, 2007, 2005, 2000, and more – Insurance industry almost pulled out – Government and industry agreement on Flood Re as preferred solution
- 10. 10Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 PAST CHALLENGES FOR INLAND FLOOD RISK Characteristics that have not been well understood: FREQUENCY SEVERITY CHANGING ENVIRONMENT SPATIAL EXTENT SPATIAL VARIABILITY WATER DEPTH
- 11. 11Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 EVENT CHARACTERISTICS VARY SIGNIFICANTLY: FREQUENCY OF SEVERE EVENTS ANNUAL ANNUAL DECADAL DECADAL>ANNUAL
- 12. 12Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 ~WEEKS ~HOURS TO DAYS ~DAYS ~DAYS TO WEEKS ~HOURS EVENT CHARACTERISTICS VARY SIGNIFICANTLY: PRECIPITATION DURATION
- 13. 13Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 EVENT CHARACTERISTICS VARY SIGNIFICANTLY: AREA IMPACTED COUNTRY REGION CITY CONTINENTCITY
- 14. 14Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 INDUSTRIAL DEVELOPMENT LAND USE CLIMATE DEFENSESDRAINAGE EVENT CHARACTERISTICS VARY SIGNIFICANTLY: CHANGES IN RISK
- 15. 15Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 UNDERSTANDING THIS COMPLEX PERIL Where does it all begin? PRECIPITATION
- 16. 16Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 UNDERSTANDING PRECIPITATION IS THE FOUNDATION TO UNDERSTANDING INLAND FLOOD RISK PRECIPITATION FREQUENCY: TIMELINE OF EVENTS SEVERITY: INTENSITY OF EVENTS EXTENT: SPATIAL CORRELATION ENVIRONMENT: ANTECEDENT CONDITIONS
- 17. 17Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK TO UNDERSTAND AND MODEL INLAND FLOOD RISK RISKVULNERABILITYHAZARD
- 18. 18Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 Inundation Rainfall runoff Major and minor rivers Defenses and drainage DEVELOPING A FRAMEWORK TO UNDERSTAND AND MODEL INLAND FLOOD RISK Precipitation PRECIPITATION
- 19. 19Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK: WHY BEGIN WITH PRECIPITATION? Time RiverFlow Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation FREQUENCY: TIMELINE OF EVENTS
- 20. 20Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK: WHY BEGIN WITH PRECIPITATION? Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation SEVERITY: INTENSITY OF EVENTS
- 21. 21Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK: WHY BEGIN WITH PRECIPITATION? Correlation of monthly peak flows in Vienna (Danube) and Dresden (Elbe) Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation EXTENT: SPATIAL CORRELATION
- 22. 22Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK: WHY BEGIN WITH PRECIPITATION? How severe would the flooding be if the antecedent conditions of 2013 were combined with the extreme event precipitation observed in 2002? Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation 2013 Wetness ENVIRONMENT: ANTECEDENT CONDITIONS
- 23. 23Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 HYDROLOGICAL PROCESSES DEVELOPING A FRAMEWORK: WHERE DOES THE PRECIPITATION GO? § High resolution; 40-50 m § Less than daily time steps § Continuously for 103 years Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 24. 24Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 HIGH RESOLUTION ≠ HIGH ACCURACY DEVELOPING A FRAMEWORK: WHERE DOES THE PRECIPITATION GO? 50 m DTM, ground-truthed 5 m DTM, LIDAR Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 25. 25Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 COMPLETE NETWORK DEVELOPING A FRAMEWORK: WHERE CAN FLOODING OCCUR? Major vs. minor Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 26. 26Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 COMPLETE NETWORK DEVELOPING A FRAMEWORK: WHERE CAN FLOODING OCCUR? Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation Extensive river network defined
- 27. 27Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 COMPLETE NETWORK DEVELOPING A FRAMEWORK: WHERE CAN FLOODING OCCUR? Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation Extensive river gauge data
- 28. 28Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DRAINAGE DEVELOPING A FRAMEWORK: FACTORS THAT CAN INFLUENCE FLOOD SEVERITY Understand current design standards… and be aware of developing environments Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 29. 29Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEFENSES DEVELOPING A FRAMEWORK: FACTORS THAT CAN INFLUENCE FLOOD SEVERITY Must consider for temporary and permanent defenses Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 30. 30Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEFENSES DEVELOPING A FRAMEWORK: FACTORS THAT CAN INFLUENCE FLOOD SEVERITY What about defense failure? Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 31. 31Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 DEVELOPING A FRAMEWORK: UNDERSTANDING THE EXTENT OF POTENTIAL FLOODING EUROPE SOUTH KOREA USA Inundation Rainfall runoff Major and minor rivers Defenses and drainage Precipitation
- 32. 32Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 CONCLUSIONS Historically, inland flood risk has been a challenge to manage FREQUENCY SEVERITY CHANGING ENVIRONMENT SPATIAL EXTENT SPATIAL VARIABILITY WATER DEPTH
- 33. 33Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 CONCLUSIONS Today we have the knowledge and tools to explicitly model and understand the risk from its source FREQUENCY: Timeline of events ENVIRONMENT: Antecedent conditions SEVERITY: Intensity of events EXTENT: Spatial correlation PRECIPITATION A comprehensive modeling approach is the only way to truly understand inland flood risk
- 34. 34Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015Copyright © 2015 Risk Management Solutions, Inc. . INLAND FLOOD IS A COMPLEX AND VARIED PERIL WE NOW HAVE THE TOOLS TO UNDERSTAND AND MANAGE THE RISK
- 35. ABOUT RMSRMS is the world’s leading provider of products, services, and expertise for the quantification and management of catastrophe risk. More than 400 leading insurers, reinsurers, trading companies, and other financial institutions rely on RMS models to quantify, manage, and transfer risk. As an established provider of risk modeling to companies across all market segments, RMS provides solutions that can be trusted as reliable benchmarks for strategic pricing, risk management, and risk transfer decisions. ©2015 Risk Management Solutions, Inc. RMS and the RMS logo are registered trademarks of Risk Management Solutions, Inc. All other trademarks are property of their respective owners. 35Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015 ABOUT RMSRMS is the world’s leading provider of products, services, and expertise for the quantification and management of catastrophe risk. More than 400 leading insurers, reinsurers, trading companies, and other financial institutions rely on RMS models to quantify, manage, and transfer risk. As an established provider of risk modeling to companies across all market segments, RMS provides solutions that can be trusted as reliable benchmarks for strategic pricing, risk management, and risk transfer decisions. 35Copyright © 2015 Risk Management Solutions, Inc. All Rights Reserved. October 13, 2015
Editor's Notes
- Good morning, good afternoon and good evening, everybody. Today we present another webinar in our webinar series on flood The focus today will be on “Managing Inland Flood Risk”
- There will be two of us presenting today There is myself, Christine Ziehmann. I have a PhD in Meteorology and lead the RMS Model Product Management team and Arno Hilberts, with a PhD in hydrology, who leads the flood model development team at RMS
- What do you consider when you think of inland flooding? Most typically you might think of a large-scale riverine flood event associated with prolonged rainfall over periods of days to weeks, like those that have inundated central Europe in recent years. The most recent major event struck in June 2013, when a weather system originating from the Mediterranean brought heavy precipitation to an already wet central Europe; for example parts of Germany had observed one of the wettest months of May on record The event impacted Austria, the Czech Republic, Germany, Hungary, Poland, Slovakia, Switzerland, causing a loss of over $4 billion to the insurance industry At the other end of the spectrum you may also think of more localized surface water flooding event, similarly associated with prolonged rainfall The U.K. was affected by numerous such events throughout 2012, as the country observed one of the wettest years on record, including the wettest April and June for England and Wales since records began in 1766, whilst the summer (June, July, August) was the wettest since 1912 These events lead to thousands of claims at a cost of almost $2 billion to the insurance industry, demonstrating how even small events can accumulate to significant levels http://www.metoffice.gov.uk/climate/uk/summaries/2012/annual Link Link
- However, inland flood risk is not only driven by prolonged periods of wet weather. Short periods of intense precipitation can lead to flash flooding that can be equally damaging and costly to the industry This is an example from 2014 in Detroit, Michigan where moist tropical air met a strengthening low pressure system to produce close to record daily rainfall over the city, which in some areas fell in a period of just 4 hours Approximately 75,000 homes and businesses suffered damage, in addition to infrastructural damage to roads, bridges and sewer infrastructure, with a final economic loss approaching almost $2 billion http://www.nws.noaa.gov/hic/summaries/WY2014.pdf Link
- Flash flood isn’t the only form of inland flooding originating from short periods of intense rainfall. Many would commonly think of storm surge related coastal flooding as the dominant form of flooding associated with topical storms but these weather systems can also carry a significant volume of moisture, bringing torrential rain Tropical storm Allison inundated large parts of southern Texas when it made landfall in June 2001 and stalled over the region for just under a week, dropping an extreme volume of water, leading to significant and widespread flooding ?? Link
- But at the other end of the inland flood spectrum we must also consider longer timescales and seasonal phenomena that can lead to extreme flooding, such as monsoon rains The most memorable example of such an event is the Thailand floods from 2011, which caused devastation across the country. From May onwards the rainfall gradually increased, with the landfall of tropical storm Nock-ten in July triggering the first bout of major flooding, and flooding persisted through the remainder of the year as heavy rains continued The flooding resulted in a total of 815 deaths, with 13.6 million people affected as sixty-five of Thailand's 77 provinces were declared flood disaster zones, with over 20,000 square kilometres (7,700 sq mi) of farmland damaged. The Thailand floods represent the most costly inland flood event ever, with an economic loss over $45 billion. Link
- As we have explored, the types of inland flooding vary significantly globally, relative to the dominant drivers of flood hazard in the region, but the loss to the insurance industry is also highly variable. It would be easy to assume that the insured proportion of flood losses would be higher in the more developed insurance markets, like the U.S. and Europe. However, as we can see here, this is actually highly variable. Flood hazard has always represented a challenge for the industry and coverage typically does not come as standard, as demonstrated by the 2013 central Europe floods, where a relatively small proportion of the loss was insured. In comparison, the industry picked up a larger proportion of the Thailand floods. Not necessarily due to higher flood insurance penetration but because of the large manufacturing footprint in the country, with risks covered under global contracts. This event provided a perfect example of where an unexpected and under-evaluated source of risk snuck up on the industry
- Exploring this further, we can see there is significant variability in how the risk is managed around the globe, with differences even within regions Some countries have approached the challenge by putting in place a government backed pool to either support or bypass the insurance industry For example the NFIP scheme in the U.S. ensures that coverage is available for most of the at risk exposure in the U.S. Whereas more recent schemes like Flood Re in the U.K. or NCIF in Thailand (setup in response to the 2011 event) aim to support an active insurance industry In other countries, a significant level of hazard, combined with a belief that flood risk is a challenge to write profitably, has meant that flood insurance penetration is low, like in Germany and Italy in Europe The developing insurance markets in Asia and South America pose similar challenges but with the additional challenge of a quickly evolving environment, leading to both an increase in exposure at risk and changes in the local hazard http://www.sciencedirect.com/science/article/pii/S2212096314000072 http://www.willis.com/documents/publications/Services/International/2012/IntlAlert_Thailand_0712.pdf
- Given the challenges associated with writing flood risk, it’s not surprising that some countries have set up schemes to support or bypass the insurance industry, in order to ensure that cover is available to the public But if flood risk is such a challenge, then why aren’t more schemes in place around the world to help manage the risk? NFIP was setup in 1968 to provide insurance to flood prone communities that wished to participate in the scheme, on the agreement that those communities adopted and enforced a floodplain management ordinance. Currently there are approximately 5.1 million policies in force, with the majority in Florida (1.9M), Texas (0.6M) and Louisiana (0.5M) (http://bsa.nfipstat.fema.gov/reports/1011.htm). However, historically the scheme has paid out more than was expected when it was conceived. Coastal flood losses have dominated the major claims, including events like Katrina and Sandy. But inland flood losses have also been a source of attritional loss to the scheme and when Allison struck in 2001, losses that year to NFIP equated to 84% of premiums The significant levels of loss to the scheme compared to the premiums collected led to the Biggert-Waters act in 2012, mandating that the scheme charged actuarial rates, meaning significant increases in some premium rates In the U.K., historically flood insurance coverage has generally been provided as part of a standard insurance policy However, a series of major loss years in recent decades came to a head in 2007 when losses to the industry totaled almost $6 billion This made many U.K. insurers question whether to continue to provide flood coverage to the market and in 2009 led to a ‘Statement of Principles’ being defined by the ABI and the U.K. government on behalf of the industry This was a temporary agreement that the insurance industry would continue to provide coverage in the market until a permanent solution was found, which became the case as Flood Re was agreed in 2013 Under Flood Re, insurers continue to provide cover but the flood risk associated with the most at risk properties is ceded to the scheme The scheme is not yet active though, so it remains to be seen how successful this will be as a long term solution to managing U.K. flood risk https://www.abi.org.uk/~/media/Files/Documents/Publications/Public/Migrated/Flooding/Statement%20of%20principles%20Northern%20Ireland.pdf https://www.abi.org.uk/Insurance-and-savings/Topics-and-issues/Flooding/Government-and-insurance-industry-flood-agreement/Flood-Re-explained
- So why has flood risk historically been such a challenge to understand and manage? The key characteristics that need to be considered have traditionally not been well understood: Frequency of flooding: which has been underestimated in high hazard zones Water depth: the potential inundation depth at a specific location Severity of flooding: is not necessarily represented well by historical experience Extent of flooding: from very localized to basin wide events and the unknowns of defense failure and human intervention Changes in the environment: the location of the exposure, changes in land use, changing climate, mitigation measures and changes in defences Spatial variability of flooding: A characteristic of the flood perils is that the hazard can change over very small distances. While one building may be flooded, the next door neighbor may not
- Let’s look into these characteristic more closely, and start with the frequency of flooding. Flooding events occur on a wide range of timescales depending on the type of flooding and the region. The recurrence of the monsoon which contributed to the Thai floods of 2011 is an annual phenomenon, but it was enhanced by the landfall of tropical storm Nock ten in Vietnam, whose remnants affected Thailand. Events such as the European flooding of 2013 or the flooding following tropical storm Allison occur on much longer time sales such as decades. This can mean that often there is insufficient data from which we can understand the risk from extreme scenarios And for the forms of flooding that occur more frequently, like groundwater flooding, data on flood depth can be hard to obtain
- Fix header The duration over which precipitation falls can also be a difficult characteristic to understand and represent This is clear in the examples of flooding for hurricane Allison and the Detroit flash floods The precipitation was intense for both events but in the case of Allison, heavy precipitation feel for many days, leading to multiple1times the accumulated precipitation across almost a week
- The area impacted is a challenge because there are two characteristics that are important to consider; firstly the size of the area impacted but also the exact region impacted Flood events can impact large areas, causing flooding across river basins and geopolitical boundaries Understanding the potential extent and correlated nature of flood events is not simple But the area impacted is also significant. Intense precipitation can occur anywhere but different regions respond differently to precipitation Engineered surfaces and complex drainage systems of cities react very differently to rural regions
- The potential risk of flooding is impacted by other characteristics, that can be also difficult to maintain up to date information on Climate; is constantly changing due to many natural or anthropogenic processes, and the location and intensity of precipitation can change accordingly Industrial development; the exposure at risk is constantly changing but this can also influence the flood risk in a region Drainage systems; frequently change and how they respond to intense precipitation can be difficult to understand and can be very complex to model Land use; similar to drainage systems, can influence the flooding experienced as this influences the absorption and routing of precipitation Defences; have a major impact on the potential flooding experienced. It is vital to understand the standard of protection they provide, their quality and potential for failure. Recently temporary flood defenses are being deployed shortly before expected flooding and and will change the risk of flooding at a particular location significantly.
- Key to understanding all of the characteristics better is to go back to the underlying driving source of flooding… precipitation
- Starting the modeling process by considering precipitation enables the hazard to be modeled explicitly and begin to tackle some of these challenges that have been discussed - Beginning with precipitation enables us to better understand: Event frequency; through the explicit representation of realistic timelines of flood events Impact of environmental conditions; as this allows antecedent conditions to be explicitly resolved and evaluated, which can influence present or future flooding Spatial extent; flooding is a result of the extent of precipitation taking place, so beginning here enables you to represent realistic event footprints and understand how the hazard correlates in space Event severity; as we explored earlier, flood severity is a result of the duration and intensity of precipitation taking place, so beginning with an understanding of this characteristic enables a true understanding of the potential severity of flood events, perhaps even exceeding those of the past
- Starting the modeling process by considering precipitation enables the hazard to be modeled explicitly and begin to tackle some of these challenges that have been discussed - Beginning with precipitation enables us to better understand: Event frequency; through the explicit representation of realistic timelines of flood events Impact of environmental conditions; as this allows antecedent conditions to be explicitly resolved and evaluated, which can influence present or future flooding Spatial extent; flooding is a result of the extent of precipitation taking place, so beginning here enables you to represent realistic event footprints and understand how the hazard correlates in space Event severity; as we explored earlier, flood severity is a result of the duration and intensity of precipitation taking place, so beginning with an understanding of this characteristic enables a true understanding of the potential severity of flood events, perhaps even exceeding those of the past
- Discuss difference between the two and give examples of risk missed by only considering major.
- Also mention defended vs. undefended here