Investigating the decision thresholds for impact-based warnings in South East Asia

The move towards impact-based forecasting presents a challenge for forecasters, who must combine information not just on what the weather might be, but also on what the weather might do. Such forecasts require an integration of both likelihood and impact severity information to issue a particular weather warning. The current pre-registered study focusses on forecasters' and stakeholders’ thresholds for determining the level of impact-based warnings, set in an area of the world particularly susceptible to extreme weather events. Set in the context of one hazard (heavy rainfall or river flooding), forecasters and stakeholders from Indonesia, Malaysia and the Philippines provided hypothetical impact-based warnings for impacts of varying likelihood. Results indicated generally good alignment with the warnings implied by previously developed impact tables. In the one country where a comparison was possible (the Philippines), we did not find evidence to suggest that forecasters and stakeholders use different thresholds for issuing warnings. We suggest that warning thresholds should be subject to regular monitoring wherever in the world an impact-based approach is used.