BACKGROUND : Criminology research has traditionally investigated sociodemographic predictors of crime, such as sex,
race, age, and socioeconomic status. However, evidence suggests that short-term fluctuations in crime often vary
more than long-term trends, which sociodemographic factors cannot explain. This has redirected researchers to
explore how environmental factors, such as meteorological variables, influence criminal behavior. In this study we
investigate the association between daily ambient temperature and homicide incidence in South Africa, a country
with one of the highest homicide rates in the world.
METHODS : Mortality data was from South Africa’s civil registration system and includes all recorded deaths in the
country from 1997 to 2013 (17 years). Daily temperature was from the National Oceanographic and Atmospheric
Association of the United States and South Africa’s Agricultural Research Council. Data were analyzed using a timestratified
case-crossover design with conditional logistic regression. We delineated cases as either “definite” (ICD-10
codes X85-Y09, n = 68,356) or “probable” homicides (ICD-10 codes W25-W26, W32-W34, W50, Y22-Y24, Y28-Y29, n =
177,873). Case periods were defined as the day on which a death occurred. Control periods were selected using a
day-of-week match within the same month and district. Analyses investigated same-day and lagged effects of
maximum, mean and minimum temperature.
RESULTS : A one-degree Celsius increase in same-day maximum temperature – our a priori metric of choice – was
associated with a 1.5% (1.3–1.8%) increase in definite homicides and a 1.2% (1.1–1.3%) increase in total (definite +
probable) homicides. Significant (p < 0.05) positive associations were also observed when applying other
temperature metrics (mean, minimum) and lags (1, 0–1). The shape of the association did not display any clear
non-linearities. There was no evidence of confounding by public holidays or air pollution.
CONCLUSIONS : This study suggests a positive association between daily ambient temperature and homicide in South
Africa. This temperature-health relationship may be of particular concern in the context of climate change. The ability to include meteorological variables as a predictor of criminal activity and violent behavior could prove
valuable in resource allocation for crime prevention efforts.
Supplementary material including additional tables
and figures. Figure S1. Provincial and district boundaries of South Africa.
Figure S2. Number of districts with temperature data. Table S1
Associations between same-day maximum temperature and homicide by
district. Table S2 Associations between same-day maximum temperature
and homicide by province. Table S3 Sensitivity analyses. Table S4 Association
by age and sex between daily mean temperature and homicide.
Table S5 Association by age and sex between daily minimum
temperature and homicide.