Many of the key findings within this report involved societal aspects of warning response and risk perception. Responding to warnings is not a simple act of stimulus-response, rather it is a non-linear, multi-step, complex process. Relationships between false alarms, public complacency, and warning credibility are highly complex as well.
The vast majority of Joplin residents did not immediately take protective action upon receiving a first indication of risk (usually via the local siren system), regardless of the source of the warning. Most chose to further assess their risk by waiting for, actively seeking, and filtering additional information.
The reasons for doing so were quite varied, but largely depended on an individual‘s ―worldview formed mostly by previous experience with severe weather. Most importantly, the perceivedfrequency of siren activation in Joplin led the majority of survey participants to become desensitized or complacent to this method of warning. This suggests that initial siren activations in Joplin (and severe weather warnings in general) have lost a degree of credibility for most residents – one of the most valued characteristics for successful risk communication.
Finding #2e: Nationally, 76% of all NWS Tornado Warnings, in their totality, are false alarms. This means 24% of all tornado warnings are eventually associated with an observed tornado –indicating limited skill in differentiating between tornadic and non-tornadic events; however, 68% of EF0-1 tornadoes receive advance warning of near 12 minutes, while 94% of EF3-5 tornadoes receive advance warning of near 18 minutes, indicating an ability to better detectstrong/violent tornadoes.9 Just over half (54%) of all severe weather warnings coincide with a severe weather event, indicating moderate skill in distinguishing between severe and non-severe thunderstorms.
Recommendation #2: To improve severe weather warning response and mitigate user complacency, the NWS should explore evolving the warning system to better support effective decision making. This evolution should utilize a simple, impact-based, tiered information structure that promotes warning credibility and empowers individuals to quickly make appropriate decisions in the face of adverse conditions. This structure should:
a) lessen the number of risk signals processed before protective action is taken (finding 2b)
b) provide a non-routine warning mechanism that prompts people to take immediate life-saving action in extreme events like strong and violent tornadoes (finding 2d).
c) be impact-based more than phenomenon-based for clarity on risk assessment (finding 2a)
d) be compatible with NWS technological, scientific, and operational capabilities (finding 2e)
e) be compatible with external local warning systems and emerging mobile communications technology (finding 2a)
f) be easily understood and calibrated by the public to facilitate decision making (finding 2a)
g) maintain existing “probability of detection” for severe weather events (finding 2e)
h) diminish the perception of false alarms and their impacts on warning credibility and response (finding 2c)