River Sentry: FAR 0 and the Wolf Ratio! (Part Six)

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False Alarm Ratio (FAR) is the measure of alerts to actual events. A missed significant flood event could be a devasting failure for a Flood Early Warning System (FEWS) however, this only affects Probability of Detection ratios (POD). What if you successfully predict a flood event, issue a warning, and it still results in incredible tragedy? How do we account for this?

A missed flood event is a significant failure, but a high FAR score is a slow death of 1000 cuts. There are no free warnings, and each unconfirmed notification slowly degrades system legitimacy. This simple human behavior equation was first captured by the ancient Greek storyteller Aesop, who famously titled the fable, “The Boy Who Cried Wolf”. FEWS purveyors attempt to capture this through FAR scoring but this doesn’t capture the totality of the problem.

Flooding can be highly localized. If a flood warning is issued for a 200-square mile area affecting 10 tributaries and flooding occurs on one tributary, the FEWS was successful in predicting a flood occurring; however, this resulted in irrelevant audience notifications (AN) to 90% of the affected audience. In our discussion, the River Sentry team refers to this problem as the “wolf ratio (WR)”, further defined as irrelevant audience notifications divided by actual events on an individual tributary or AN/events = WR. The Wolf Ratio can be applied to each tributary individually and importantly, the audience that lives along those rivers.

In the next blog post, we will further explore Wolf Ratio and our “Trust” variable while revisiting the 2021 flood tragedy in Germany. First, let’s visit the River Sentry approach to addressing false alarms and ensuring trust in our approach.

River Sentry protects specific locations of valuable real estate in the goal of protecting lives, not possessions. We guard those facilities by enveloping them with redundant perimeter alarm systems designed to provide a minimum standard of responsiveness. We further expand value by allowing systems to work together to benefit from upstream warnings and provide downstream warnings.

Our devices are placed well outside high water marks and lie uninterested in the seasonal behavior of waterways. We provide essential interventions to prevent dangerous flooding from becoming deadly. We focus on accomplishing this single important task to the apex of technological capability. Since significant flooding must occur somewhere to trigger a Sentry defensive line, barring nefarious intervention, a false alarm simply isn’t possible.

This is the formula for FAR 0 and with it, Wolf 0. Combined zero scoring equates to a high trust (T) factor. For the next post, we will return to the tragic events of Ahr Valley, site of the second deadliest flooding disaster in German history.

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