FATHOM US

Fathom-US 2.0 provides the most comprehensive view of flood hazard across the United States and is a unique combination of inland and coastal flooding based on the latest science and datasets.

For anybody seeking to understand US flood exposure, Fathom-US 2.0 provides the complete picture.

Please contact us if you would like to know more about Fathom-US 2.0.

10 metre resolution

10 return periods from
1:5 years to 1:1000 years

Climate
change

Updated 2020
climate state
and future
climate state

Flood
defences

Most complete flood
defence dataset built
with input from multiple
agencies. Independent
validation of levee
information

Coastal
flooding

Complete coastal
modelling using
MIT hurricane model
with over 50,000 events
for storm surge

Inland
flooding

Total representation of
fluvial and pluvial flooding.
Simulation of flooding
for all river channels,
irrespective of size, from
smallest to the biggest

Climate change is anticipated
to alter many of the Earth’s
weather patterns, including extreme
temperatures, precipitation and
hurricane intensity

2020

2050

Fathom have partnered with world leading scientists to undertake the most comprehensive modelling of the United States ever attempted.

Both the inland and coastal flood hazards have been modelled under a 2020 climate scenario and are not based solely on historical records.

For example, in the coastal flood modelling, sea levels have been raised to represent the current 2020 levels, and synthetic hurricanes used to represent changing storm surge intensity.

Our 2020 simulations provide an updated view on today's risk. Particularly given changes to sea-level and sea-surface temperature, basing models on historical observations alone is likely to underestimate exposure.

Fathom have built future flood scenarios for 2020, 2035 and 2050 time horizons. We are simulating multiple realisations under the RCP 4.5 concentration scenario.

Fathom-USv2 provides projections of fluvial, pluvial and coastal flood inundation. This also includes explicit modelling of changing hurricane intensities. We are modelling changing precipitation, river discharge, sea-level rise and storm surge intensity.

Sea-level rise

Sea-surface temperature

Observation: EPA
Projection: IPCC

Fathom-US 2.0 will fundamentally change our understanding of flood risk both now and in the future.

The coastal flooding is based on the storm surge from high tides and atmospheric events.

The entire US coastline has been modelled for coastal flooding for high tides and atmospheric events, including explicit storm surge modelling using synthetic hurricanes and the specific simulation of compound flooding (the joint occurrence of higher river flows and coastal storm surge)

>50,000

synthetic hurricanes from the Massachusetts Institute of Technology have been used to account for changing hurricane behaviour.

Updated 2020 and 2050 view of hazard with the impacts of changing atmospheric and sea-level conditions explicitly modelled.

Flooding modelled for extreme high tides and storm surge.

Both east and west coast USA.

Compound flooding explicitly represented.

Tide, surge and wave set up modelled, in addition to fluvial and pluvial flooding.

Large hurricane event set included.

Comparison between
2020 and 2050
100 year storm surge

Blue - 2020

Comparison between
2020 and 2050
100 year storm surge

Blue - 2020

Red - 2050

Fathom have modelled the entire US coastline for coastal flooding

Fathom-US 2.0 fluvial models cover every watercourse from the largest river down to the smallest stream.

10m resolution nationwide.

Channels explicitly represented.

100% coverage of contiguous US.

Flows generated from entire USGS gauge record.

Multiple return periods.

Comprehensive defence representation.

Comparison of a remotely sensed Midwest flood event with Fathom fluvial data -

Planet data

Surface water

Comparison of a remotely sensed Midwest flood
event with Fathom
fluvial data -

Fathom-USv2
fluvial hazard data

0.5m

Inland flood models
are based on the latest
US government terrain
and river data

Fathom’s pluvial
models represent
flash-flooding
nationwide

10m resolution nationwide.

Channel drainage explicitly represented.

100% coverage of contiguous US.

Flooding simulated for even the smallest flow pathways.

Extreme precipitation magnitudes from NOAA.

Multiple return periods.

Representing flood defences
is critical, however existing
defence datasets are
substantially incomplete

Undefended

Defended

To help address this key issue, Fathom funded a PhD resulting in the development of an automated flood defence detection algorithm.

Fathom have built out the most complete flood defence dataset built with input from multiple agencies and independently validated.

This has included a collaboration with the US Army Corps of Engineers and with First Street Foundation and their dedicated levee development team.

This team spent over a year focusing solely on sourcing missing levee, dam and storm water infrastructure information from across the US which have been included in Fathom-US 2.0, creating the most complete dataset currently available.

Fathom are now working with FEMA and the US Army Corps of Engineers to update their levee databases.

Fathom’s work has
proven that current
methods significantly
underestimate flood risk

FEMA capture
major rivers only

FEMA’s flood hazard data are a patchwork of small scale ‘traditional’ flood models.

In many areas these models are outdated, with some dating back to the 70s and 80s.

Currently 75% of these maps are deemed to be out of date and 40% of the country hasn’t even been covered.

Fathom-US
captures all
river channels

Collaborative work with the US Environmental Protection Agency suggests a 3 fold increase in total exposure to a 100 year flood

Fathom-US 2.0 was validated against the entire FEMA flood hazard catalogue, identifying that current FEMA data misses around three quarters of total flood exposure nationwide.

According to FEMA, 13 million Americans are exposed to risk from the 100 year flood. Fathom data suggests differently.

FEMA identified 13 million Americans are exposed
to 100 year flood

13M

Unlike FEMA data, Fathom's accurate, peer-reviewed research has found that 41 million Americans are at risk from a 100 year flood event.

Fathom identified
41 million Americans are exposed to 100 year flood

41M

Fathom-US 2.0 has been subjected to an unprecedented level of independent validation

Firstly, the methods build on Fathom’s award-winning validation work comparing models against FEMA flood hazard data, where they exist.

Next, the Fathom models have been compared to high-quality, multi-million-dollar models from the Iowa Flood Center.

Lastly, in an unprecedented piece of validation work, Fathom-US 2.0 has been scrutinized by an independent team at a detailed local level over a
12-month period.

Significant human resource was deployed for identification and characterisation of flood adaptation features such as levees, storm drains and dams.

The model was compared to high-quality FEMA flood maps and data, local records and claims history to identify any errors or discrepancies in the data resulting in poor model behaviour. The model was then updated with any missing infrastructure, terrain data or channel modifications and re-run, resulting in the final Fathom-US 2.0 data.

Fathom have partnered with First Street
Foundation on the development of
Fathom-US 2.0 for over 2 years.

The Fathom data underpins First Street’s new Flood Factor™, a free, online tool that makes it easy to learn if a property has flooded from major events in the past, if it is currently at risk, and how that risk is likely to change in the future.

Flood Factor™ simplifies flood risk information so anyone can discover their risk, understand the science, and make informed decisions to prepare for the future. It is due to be launched later this month.

Visit site

Academic validation

Read Paper

Validation of Fathom-US flood hazard model

Water Resources Research, 2017

Press

Cool Green Science

New Study Shows Flood Risks Across the U.S. are Underestimated
(in a Big Way)

Press

BBC News

US flood risk 'severely underestimated'

Press

Science Daily