Are you hot and bothered by all this good weather? Has the lightning terrified you? Have you considered suicide recently? The effects of weather on behaviour in general and crime and suicide in particular have been intensively studied, though psychologists' conclusions are still heavily clouded (albeit with occasional sunny intervals).

"The effects of weather on homicide" was the title of a paper by Derral Cheatwood in the Journal of Quantitative Criminology in 1995. The research was based on a correlation between murder rates and weather conditions in Baltimore, Maryland, over a period of eight years. The results showed a small but statistically significant correlation: "The consistent meteorological measure of importance is [the] number of previous days in a row in which the discomfort point (a specific point on the temperature and humidity index) has been over the psychologically relevant level of 79." The writer also concluded, however, that "the repertoire of habits and adaptations available to the individual conditions his or her reactions to physiological stress induced by the weather." In other words, if it's hot and sticky enough, murderers may be more inclined to murder. Or they may decide not to.

A more detailed survey by Ellen Cohn entitled "Weather and Crime" may be found in the winter 1990 issue of the British Journal of Criminology. The research reveals that: "assaults, burglary, collective violence, domestic violence, and rape tend to increase with ambient temperature, at least up to about 85F. The relationship between heat and homicide is uncertain. High temperatures do not appear to be correlated with robbery, larceny and motor vehicle theft." They conclude that "the most violent crimes against persons increase linearly with heat, while property crimes are not strongly related to temperature changes." The 85F threshold is interesting, with its implied suggestion that when it gets really hot, even violent criminals can feel too exhausted to go about their daily business.

A later paper, "The effect of temperature on crime", by Simon Field (British Journal of Criminology, 1992), reached a similar conclusion about the effect of temperature on violent crime, but also found a link between high temperatures and crimes against property.

Interestingly, violence and weather also appear to be linked in cases of suicide and attempted suicide. In "Synchronised annual rhythms in violent suicide rate, ambient temperature and the light-dark span" (Acta Psychiatrica Scandinavica, 1994), a team of researchers reported that "occurrence of violent suicide was significantly and positively related to ambient temperature, sunlight duration and an increase in temperature over the preceding weeks". But no relationships were found between weather conditions and non-violent suicide rates. In 1994, however, the British Journal of Psychiatry published the results of a survey of 7,693 women's and 4,686 men's suicide attempts ("Seasonal and weather factors in parasuicide" by A Barker et al) and found "small but highly significant correlations" between parasuicide rate and weather parameters, particularly for women. "Gender differences in body temperature regulation may account for observed sex differences."

Meanwhile, in California, it has been found ("Suicides in California, 1968-1977" by G Tietjen and D Kripke; Psychiatry Research 1994) that in Sacramento fewer people commit suicide in the fourth week after a particularly sunny spell. Weather and suicide, however, had no correlation in Los Angeles.

On the more specific matter of the recent lightning, "Illusions (and shattered illusions) of invulnerability: Adolescents in natural disaster" by L Greening and SJ Dollinger, (Journal of Traumatic Stress, 1992) reported that "even when negative emotional effects have dissipated, natural disasters can have lasting consequences for adolescents' perceived sense of vulnerability to similar future events." Subjects from towns that had experienced severe lightning strikes were more likely to be worried about being killed by lightning - and these effects may last for as long as seven years.

We end with a finding that, unlike most of the above, appears to be definitive. In "Decision making with probability forecasts of rainfall" (Psychological Reports, 1989), YNakajima and H Ohta report the results of a survey into individuals' decisions on whether to carry an umbrella. The figures clearly showed that the more it rained, the more people carried umbrellas.

William Hartston (With the help of data from Ovid's PsycLIT database)

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