On August 22, 2022, parts of the Dallas-Fort Worth area saw as much as 15 inches of rain in an 18-hour period, causing significant flood damage. Early estimates put estimated damages and economic losses somewhere around $6 billion. Unfortunately, this wasn’t a one-off event.
Earlier in August, a similar heavy rain event drenched southeastern Illinois with an estimated 10-13 inches of rain in just hours. Death Valley National Park in California saw a year's worth of rainfall in three hours shutting down every road inside the park. In late July, St. Louis, Missouri recorded a record rainfall 9.07″ within any 24-hour period. The same weather system caused far more destruction in Eastern Kentucky, where torrential rains ran off the area’s mountainous landscape.
Some coined the summer of 2022 as “America’s summer of floods.” And the trend seems to be continuing. Many believe that climate change is pushing more frequent and intense rainfall that is resulting in more flooding events. According to the , the amount of rain falling in the heaviest rainstorms increased across the country between 1958 and 2016. Recent rainfall events and subsequent floods seem to support this data. (For more about increasing flood risks, read Bruno D’Urso’s recent article: Making history: Flood risk is rising.)
Underestimating flood risk
A growing body of research has found that current flood maps relied on to estimate the risk of flooding are falling short, underestimating potential risk, especially as climate change gets worse.
According to FEMA's flood maps, about 12% of properties in three of the hardest-hit Kentucky counties are in what the agency calls a "Special Flood Hazard Area," a zone that would be inundated during a 1-in-100-year flood event. Typically, when homeowners get mortgages in the area, they're required to purchase flood insurance. However, according to estimates by climate research nonprofit , a more accurate flooding model that takes climate change into consideration puts 51% of properties in those counties at risk for flood. As a result, most impacted by the floods in Kentucky did not have flood insurance.
The destruction in Eastern Kentucky is a warning for other communities around the US that once-unthinkable floods are becoming more common due to climate change. Federal flood zone maps used by the insurance industry substantially underestimate the risk in many parts of the country, and the nation as a whole is underprepared for the financial ruin left in the wake of powerful floods.
A growing body of research has found that current flood maps relied on to estimate the risk of flooding are falling short, underestimating potential risk, especially as climate change gets worse.
Seeking improvements
In Kentucky, FEMA flood maps for three of the hardest-hit counties in Kentucky, including Breathitt, Clay and Perry counties, had not been updated in more than 14 years, according to federal records. This doesn’t appear to be a fluke. A published in February 2022 found that almost 85% of the flood damage events reported to the National Oceanic and Atmospheric Administration between December 2006 and May 2020 took place outside FEMA's flood risk zone.
The U.S. Government in late 2021 that found while FEMA’s Risk Mapping, Assessment, and Planning (Risk MAP) program has increased its development of flood maps and other flood risk products, the agency faces challenges making sure that its maps comprehensively reflect current and future flood hazards.
Through , FEMA is updating the nation’s coastal and , where appropriate. FEMA is publishing new flood maps of densely populated areas that were not previously mapped and is working with local community officials to produce additional data and hazard mitigation tools that will enable more strategic emergency preparedness, planning and risk reduction in coastal communities.
One big issue with current FEMA flood maps is that they only addressing flooding along the coast or from major rivers. They do not consider the possibility of flash floods such as those seen in Kentucky when intense rainstorms overflowed small streams and municipal sewer systems. FEMA maps really only consider major river channels and coastal flooding, not rainfall or small waterways. Again, such an information gap leaves out huge portions of the country that are susceptible to rainfall-driven flooding as recently witnessed.
FEMA’s flood maps depict current levels of disaster risk using data from the past, not potential future risk. Even FEMA recognizes its maps shortcomings. Given climate change, FEMA estimates that the size of areas with a high flood risk will increase by 55 percent along the nation’s coastlines and up to 45 percent along major river systems by the end of the century.
More inclusive modeling
Other available mapping resources take more data into account. Insurers, like the 色多多视频companies, therefore are supplementing use of FEMA’s maps to fills the data gaps. For instance, UK-based JBA, a global hydrology company, is considered the flood market standard in many countries. They bring 27 years of experience in Consulting to National and Regional Governments and are considered the flood market standard in many Countries. JBA is one of the few companies fully dedicated to flood risk modelling.
JBA Hazard Maps are globally consistent models with whole country coverage and include:
- River (fluvial) Flood- Globally at 6 Return periods 1:20 – 1:1500 years
- Surface (pluvial) Flood- Depth of water above ground provided
- Municipal Flood protection data
- High resolution elevation data 5m in Western Europe 30m ROW
- Areas protected against flood, with Standard of Protection (flooding return period to which the protection is effective)
The hazard data provided by JBA is the best available global flood dataset. It fills the data gaps with FEMA and is more up to date in many hazard areas. JBA has also recently published a new version of USA flood hazard layers, with high resolution (5 m) and flood protection information from USACE and proprietary analysis.
The JBA depth is a calculation using their hydrological model on the expected height of water above ground level. Currently this is provided in bands, but in future, will use the actual depth result which will further improve the damage ratios.
JBA hazard data has been tested against AXA XL’s claims data for the last 5 years. In that time, all large flood events have been checked at location level and the data has performed well. For example, for Hurricane Harvey in 2017, JBA data was validated against double the number of locations identified by FEMA. In the European floods in 2021, 90% of large flood impacted sites analyzed were identified as flood exposed by the JBA data. In addition to our tests, JBA regularly performs large-scale tests of their global flood models against historical events.
The resolution of the Digital Terrain Model (DTM) used for the development of flood hazard map has a major impact on the quality and reliability of results. If we consider an area mapped to 90m resolution, then the area is grided to 90mx90m grids and a single elevation point is taken in each 90m grid point. If we have 30m resolution, then in the same 90m grid we now have 9 elevation readings. This significantly improves the models understanding of relative elevation. If we go from 30m to 5m then we get an additional 35 elevation points. JBA provides a 5m resolution model in most of the countries and 30m in ROW, which is very high compared to other vendors and hazard maps at global or national level. Understandably, local hazard maps (at regional or municipal) level might reach higher resolutions. Such maps might be adopted by Risk Engineers to complement the JBA information, where applicable and relevant.
Better flood risk assessment
As mentioned earlier, FEMA estimates that climate change will continue to impact flood risk, expecting to see high flood risk areas to increase by 55 percent along the nation’s coastlines and up to 45 percent along major river systems by the end of the century. Using enhanced modeling, property insurers too can expect to see more locations exposed to floods. However, of the flip side, the High-resolution data means that the flood zone may be more refined than shown in other mapping. For others this means that their flood risk could be less than initially modelled.
More accurate assessment of flood risk will also allow for better preparedness. Businesses in flood-prone areas benefit from guidance from AXA XL’s Property Risk Engineers to lessen damage and business interruption. At facilities at risk from flooding, risk consultants work with a business to identify and understand its flood exposures. While preventing a flood from occurring is often not possible, the team can help businesses work through recommendations designed to minimize the effect of flooding and improve business resilience. This can include physical protection as well as contingency planning. Having a specific flood emergency response plan as part of an overall business continuity management strategy is essential.
As the saying goes, when it rains, it pours. In some recent cases, that’s meant downpours and floods. After this summer of floods, it is hard to deny that potential changes in climate are not impacting rainfall amounts.
Fortunately, more data and modelling tools are available to compliment the tools and data that have been relied on for so long. Employing what other modeling tools and data available is helping the Federal Government, local communities, insurers, and others enhance their flood assessments. More accurate assessments will lead to better protection.
About the Authors
Jeff Williams is Product Line Leader for AXA XL’s North America Property team. He can be reached at jeff.williams@axaxl.com.
Bruno D’Urso is a Risk Engineering Lead for 色多多视频Risk Consulting. Bruno can be reached at bruno.durso@axaxl.com.
