Forecasting hazards, averting disasters

6.2.2   Defining triggers

In rapid-onset crises defining the trigger is more 

straightforward than a slow-onset crisis, where the 

trigger may be a combination of rainfall forecasts and 

other weather-related indicators, as well as changes 

in prices of food and other commodities, politics, etc. 

How the trigger is defined will affect how accurate the 

forecast is, the likelihood of acting in vain and therefore 

the overall cost-effectiveness of the response. Crises often 

arise as a result of the interplay of changes in rainfall, 

vegetation and prices, as well as other factors. As a result, 

the cost-effectiveness of a response can be fundamentally 

affected by the composition of indicators used to trigger 

it, and these will vary according to the context and types 

of livelihoods affected by the disaster.