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🖥️ '''Natural catastrophe model''' is a computational framework used by [[Definition:Insurance carrier | insurers]], [[Definition:Reinsurance | reinsurers]], [[Definition:Insurance broker | brokers]], and [[Definition:Capital markets | capital markets]] participants to estimate the probability and financial impact of [[Definition:Natural catastrophe (Nat Cat) | natural catastrophe]] events on portfolios of insured risk. These models — developed and maintained by specialist vendors such as [[Definition:Moody's RMS | Moody's RMS]], [[Definition:Verisk | Verisk]] (formerly AIR Worldwide), and CoreLogic, as well as through proprietary tools built by large reinsurers — simulate thousands or millions of potential catastrophe scenarios across perils including hurricanes, earthquakes, floods, wildfires, and severe convective storms. The output feeds directly into [[Definition:Underwriting | underwriting]] decisions, [[Definition:Reinsurance | reinsurance]] purchasing, [[Definition:Pricing | pricing]], [[Definition:Capital management | capital management]], and [[Definition:Regulatory capital | regulatory capital]] calculations, making Nat Cat models one of the most consequential analytical tools in the property insurance value chain.

🔬 A typical Nat Cat model comprises four interconnected modules. The ''hazard module'' generates a stochastic event set representing the full range of plausible catastrophic events — their frequency, location, and physical intensity — based on historical data, geophysical science, and climate research. The ''vulnerability module'' estimates the damage each simulated event would inflict on different building types, infrastructure, and contents, translating physical hazard into structural loss. The ''exposure module'' ingests the user's portfolio data — property locations, construction types, occupancy classes, and [[Definition:Total insured value (TIV) | insured values]] — and maps it against the hazard and vulnerability outputs. Finally, the ''financial module'' applies [[Definition:Policy terms and conditions | policy terms]], [[Definition:Deductible | deductibles]], [[Definition:Policy limit | limits]], and [[Definition:Reinsurance | reinsurance]] structures to convert gross damage estimates into net financial losses for the insurer. This architecture allows users to generate key risk metrics such as [[Definition:Probable maximum loss (PML) | probable maximum loss]], [[Definition:Average annual loss (AAL) | average annual loss]], and [[Definition:Exceedance probability curve | exceedance probability curves]].

⚠️ Despite their sophistication, Nat Cat models carry significant uncertainty — an issue that regulators, rating agencies, and the industry itself have become increasingly candid about. Model outputs are sensitive to assumptions about event frequency, climate trends, building vulnerability, and exposure data quality, and different vendor models can produce materially different loss estimates for the same portfolio. The divergence became especially visible after events such as the 2011 Tōhoku earthquake and tsunami and the 2017 Atlantic hurricane season, where actual losses challenged model expectations. Regulatory frameworks respond to this model risk in different ways: [[Definition:Solvency II | Solvency II]] in Europe permits approved internal models for capital calculations but subjects them to rigorous validation; [[Definition:Lloyd's of London | Lloyd's]] mandates the use of approved vendor models for [[Definition:Realistic disaster scenario (RDS) | realistic disaster scenarios]]; and rating agencies such as [[Definition:AM Best | AM Best]] and [[Definition:S&P Global Ratings | S&P]] incorporate model outputs into their capital adequacy assessments while applying their own adjustments. For the industry, the ongoing challenge is to refine these models in the face of [[Definition:Climate change | climate change]], evolving exposure patterns, and emerging perils — ensuring that the tools remain fit for purpose as the risk landscape shifts.

'''Related concepts:'''
{{Div col|colwidth=20em}}
* [[Definition:Natural catastrophe (Nat Cat)]]
* [[Definition:Probable maximum loss (PML)]]
* [[Definition:Average annual loss (AAL)]]
* [[Definition:Catastrophe reinsurance]]
* [[Definition:Exposure management]]
* [[Definition:Natural catastrophe modeling]]
{{Div col end}}

Definition:Natural catastrophe model - Revision history

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