The Marginal Value of Weather Warning Systems

Benjamin M. MillerUniversity of California, San Diego

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What causes disaster deaths?

What causes disaster deaths?

U.S. Tornado Warning History & Infrastructure

• First successful tornado warning– Tinker Air Force Base, Oklahoma City, 1948– National Weather Service begins Watch/Warning system in

1953

• Outdoor Warning Sirens– Originated as air-raid sirens in WWII.

• NOAA Weather Radio/SAME Receiver– NOAA now has over 1,000 transmitters which cover most of the

U.S.

• Television/Radio– Warnings issued through the EBS/EAS

• Commercial Mobile Alert System

Research Question

• Do warning systems causally reduce deaths and injuries?

How much?• NOAA radio

transmitters

In the Literature• Responsiveness to warning systems is mostly case

studies: Balluz et. al (2000)

Survey of 146 individuals following March 1, 1997 tornadoes in Arkansas

Liu et. al (1994) Survey roughly 194 households in two Alabama areas after tornado

warnings. “In the area without sirens, only 28.9% of 194 respondents heard a

tornado warning of these, 73.2% first received the warning from radios or television. In the area with sirens, 88.1% of 193 respondents heard a warning, and 61.8% first received the warning from a siren.”

• These are great, but the counter-factual is not clear. How would people have fared without a particular warning system?

Identifying Variation• Transmitter broadcast area– Very endogenous: correlated with population density and

other factors correlated with the number of fatalities and injuries.

– Could control for some but not all of these factors

• Date of transmitter installation– Compare tornado outcomes between counties which both

eventually get transmitter coverage– Compare tornado outcomes within the same county

before/after transmitter installation– In either case, can’t control for concurrent regional changes

Data• Tornado Characteristics

57,120 recorded tornadoes from 1950-2012 Counties passed through (Enhanced) Fujita scale Death, injuries, and sometimes damages

State-tornado level

• County Characteristics Which transmitters broadcast in the county, date of

installation/deactivation County-level population data from Decennial Census, with

annual intercensal estimates State-decade-level housing types (ex. mobile, detached house,

etc.) from the Historical Census of Housing

Number of Tornadoes,1950 - 2012

Number of EF3+ Tornadoes,1950 - 2012

Number of NOAA Transmitters: Jan 1, 1950

Number of NOAA Transmitters: Jan 1, 1960

Number of NOAA Transmitters: Jan 1, 1970

Number of NOAA Transmitters: Jan 1, 1980

Number of NOAA Transmitters: Jan 1, 1990

Number of NOAA Transmitters: Jan 1, 2000

Number of NOAA Transmitters: Jan 1, 2010

Empirical Analysislog(Fatalities/Injuries/Property Damagei) =

β[Transmitter Coverage]i + γ[Controlsi] + εi

• Transmitter Coverage One or more transmitters broadcasting over the tornado path β is the percent change attributed to transmitter coverage

• Controls Population, Date of transmitter installation, (Enhanced) Fujita

Scale, Path length, State Fixed Effects, Month & Year Fixed Effects, Distribution of home types

Could add income, county size, demographics... County FE

• Count Data OLS biased, use Poisson regression

Conclusion

• Significant causal reduction in injuries and fatalities On average, about 30% reduction• Most causal prevention of deaths/injuries comes

from higher EF Scale tornadoesOther stuff: Any benefit from multiple transmitters? Benefits decline over time as replaced by new

technology?• Importance for choosing optimal investment within

and across warning systems

Thank you!

Any and all comments/suggestions are completely welcome.