1. Introduction

This report focuses on a Hurricane Ida case study, employing a multi-hazard framework to attribute extreme event impacts and economic damages.

2. Methods

The methodology merges the reanalysis of the 2021 hurricane with physical modelling for climate change effects. The model varies changes as a linear function of wind speed, from “zero percent change to the weakest winds up to 9% [p. 4]” for the strongest.

2.1. Hurricane wind simulation

Wind fields are generated reflecting scenarios from 2021, 1971, and 2071.

2.2. Wind impact data and modeling

Calculations were based on structures with “at least $5000 damages to structure and contents [p. 7]”.

2.3. Storm surge data and modeling

The study links wind fields to storm surge flood models.

2.4. Structural and geographic data

Geographic data is leveraged to project damages in south Louisiana.

3. Results

Results demonstrate significant increases in impacts associated with climate change.

3.1. Wind and storm surge levels

Simulations generate “stronger peak wind speeds for the 2071 hurricane, 9% higher than the 2021 hurricane [p. 7]”. The 1971 storm simulation resulted in winds “3% lower than the 2021 storm [p. 7].”

3.2. Attribution of extreme weather event impacts

“Total damages from Hurricane Ida were 19% higher in 2021 than they would have been in 1971 [p. 2]”. Damages could be “76% higher in 2071 [p. 2]” compared to 2021.

3.2.1. Total damages

Baseline damages in the 1971 scenario are estimated “as $4.7 billion [p. 7].” For wind impacts, “total damages in a counterfactual 1971 climate totaled approximately $2.2 billion [p. 8].” Under 2021 conditions, “this figure rises to $2.9 billion—an increase of $713 million [p. 8].” Projected wind damages reach “$6.4 billion for an Ida-like storm in 2071 [p. 8],” a “194% increase over the 1971 baseline [p. 8].” Storm surge damages totalled “$2.5 billion in the 1971 simulation and rose to $2.7 billion in 2021 [p. 8].” For 2071, storm surge damages will “grow to $3.4 billion [p. 8], marking a 36% increase relative to 1971 [p. 8].”

3.2.2. Number of affected structures

Under 2021 conditions, “74 700 structures [p. 8]” experienced wind damage. For 2071, this reaches “113 500 structures [p. 8].” For storm surge, “20 600 structures [p. 9]” were affected in 2021, including “1300 (6%) [p. 9]” that would not have flooded in 1971. By 2071, this reaches “26 400 [p. 9].”

3.2.3. Regional differences

Damages in highly affected areas are “25%–50% higher from 1971 to 2021 [p. 11]”.

3.2.4. Differences by structure type

Residential structures accounted for “roughly 70% of wind-related damages [p. 13]”. For wind, there were “between 24% and 28% lower damages [p. 13]” in 1971 compared to 2021. Between 2021 and 2071, industrial structures saw the “highest increase (145%) [p. 13].” For storm surge, residential structures saw “7% fewer impacts [p. 14]” in 1971 compared to 2021. From 2021 to 2071, “31% greater impacts [p. 14]” were projected for residential structures, with increases of “18%, 13%, and 12% [p. 14]” for industrial, commercial, and public.

4. Discussion and conclusion

Wind damages are projected to rise faster than storm surge damages.