What Triggers A Catastrophe Bond?

The sponsor and investment bank who structure the cat bond must choose how the principal impairment is triggered. Cat bonds can be categorized into four basic trigger types.[5] The trigger types listed first are more correlated to the actual losses of the insurer sponsoring the cat bond. The trigger types listed farther down the list are not as highly correlated to the insurer's actual losses, so the cat bond has to be structured carefully and properly calibrated, but investors would not have to worry about the insurer's claims adjustment practices.
Indemnity: triggered by the issuer's actual losses, so the sponsor is indemnified, as if they had purchased traditional catastrophe reinsurance. If the layer specified in the cat bond is $100 million excess of $500 million, and the total claims add up to more than $500 million, then the bond is triggered.
Modeled loss: instead of dealing with the company's actual claims, an exposure portfolio is constructed for use with catastrophe modeling software, and then when there is a large event, the event parameters are run against the exposure database in the cat model. If the modeled losses are above a specified threshold, the bond is triggered.
Indexed to industry loss: instead of adding up the insurer's claims, the cat bond is triggered when the insurance industry loss from a certain peril reaches a specified threshold, say $30 billion. The cat bond will specify who determines the industry loss; typically it is a recognized agency like PCS. "Modified index" linked securities customize the index to a company's own book of business by weighting the index results for various territories and lines of business.
Parametric: instead of being based on any claims (the insurer's actual claims, the modeled claims, or the industry's claims), the trigger is indexed to the natural hazard caused by nature. So the parameter would be the windspeed (for a hurricane bond), the ground acceleration (for an earthquake bond), or whatever is appropriate for the peril. Data for this parameter is collected at multiple reporting stations and then entered into specified formulae. For example, if a typhoon generates windspeeds greater than X meters per second at 50 of the 150 weather observation stations of the Japanese Meteorological Agency, the cat bond is triggered.
Parametric Index: Many firms are uncomfortable with pure parametric bonds due to the lack of correlation with actual loss. For instance, a bond may pay out based on the wind speed at 50 of the 150 stations mentioned above, but the insurer loses very little money because a majority of their exposure is concentrated in other locations. Models can give an approximation of loss as a function of the speed at differing locations, which are then used to give a payout function for the bond. These function as hybrid Parametric / Modeled loss bonds, and have lowered basis risk as well as more transparency.[6