Global Flood Map Methodology Documentation

The report outlines the technical process of combining Fathom's Global Flood Map (v3.1) with Public Safety Canada's residential building data and probabilistic vulnerability functions. It describes the use of 'big data' from US FEMA insurance claims to model damage distributions across 10 residential building types. The methodology accounts for flood defenses based on urbanization levels and applies the trapezium rule across eight return periods to estimate economic losses. Results show that Canada's defended AAL is projected to increase from 1,423 million CAD in 2020 to 1,681 million CAD by 2050, while undefended AAL is significantly higher, reaching 5,050 million CAD by 2050.

• The methodology employs probabilistic vulnerability functions derived from over 2 million flood insurance claims from the US Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP) to capture the empirical relationship between flood depth and damage.
• Damage response is modeled using a bimodal beta distribution, indicating that flooded buildings typically experience either minor or catastrophic damage, with the distribution shifting toward 100% damage as flood depth increases.
• The loss modeling assumes a universal ground floor height of 0.2 m for residential buildings, which is subtracted from the sampled hazard map depth to determine the 'depth above ground floor'.
• Flood defenses are estimated by combining urbanization levels from the Global Human Settlement Layer with global defense standards (FLOPROS) and local data from Risklayer, assuming that defense standards are highest in urbanized areas.
• Average Annual Loss (AAL) is calculated using the 'trapezium rule' across eight fixed return periods: 1 in 5, 10, 20, 50, 100, 200, 500, and 1000 years.
• For defended scenarios, Canada's total residential AAL is projected to rise from 1,423 million CAD in 2020 to 1,503 million CAD in 2030 and 1,681 million CAD in 2050.
• In undefended scenarios, the projected AAL for Canada is substantially higher, increasing from 4,808 million CAD in 2020 to 5,050 million CAD by 2050, with British Columbia showing the highest individual provincial loss in 2050 at 2,375 million CAD.

APA

Wing, D. O. (2024). Global Flood Map Methodology Documentation. Canadian Climate Institute. https://climateinstitute.ca/wp-content/uploads/2025/01/Fathom-Climate-Institute-climate-adjusted-flood-risk-modelling.pdf

Chicago

Wing, Dr Oliver. Global Flood Map Methodology Documentation. Canadian Climate Institute, 2024. https://climateinstitute.ca/wp-content/uploads/2025/01/Fathom-Climate-Institute-climate-adjusted-flood-risk-modelling.pdf.

Wikipedia

{{cite report |last1=Wing |first1=Dr Oliver |title=Global Flood Map Methodology Documentation |publisher=Canadian Climate Institute |date=24 May 2024 |url=https://climateinstitute.ca/wp-content/uploads/2025/01/Fathom-Climate-Institute-climate-adjusted-flood-risk-modelling.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{wing2024global, author = {Wing, Dr Oliver}, title = {{Global Flood Map Methodology Documentation}}, institution = {Canadian Climate Institute}, year = {2024}, month = may, url = {https://climateinstitute.ca/wp-content/uploads/2025/01/Fathom-Climate-Institute-climate-adjusted-flood-risk-modelling.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }