A study analyzing crime data in Philadelphia for 10 years found that rates of violent crime and disorderly conduct are higher when the weather is warmer and more pleasant, even rising sharply during warmer-than-typical winter days.
The research, conducted by Dr. Leah Schinasi, assistant research professor, and Dr. Ghassan Hamra, assistant professor, both of Drexel University Dornsife School of Public Health, is published in the Journal of Urban Health and uses a time series analysis of associations between temperature and crimes in Philadelphia, PA, for years 2006-2015.
The study used daily crime data from the Philadelphia Police Department, and hourly temperature and dew point data from the National Centers for Environmental Information. The team calculated the mean daily heat index and daily deviations from each year’s seasonal mean heat index value and found associations were strongest with violent crime and disorderly conduct.
For example, when the heat index (a metric that uses temperature and humidity to represent human comfort) was 98 degrees, rates of violent crime were 9 percent higher compared to days when the temperature was 57 degrees. When it came to rates of disorderly conduct, they were 7 percent higher on 98-degree days than on 57-degree days.
During the year’s colder months — October through April — the contrast of high versus low rates of crime on more comfortable versus cooler temperature days was more striking. When temperatures reached 70 degrees during that period, daily rates of violent crime were 16 percent higher, on average, and disorderly conduct rates were 23 percent higher, compared to 43 degree days, the median heat index for that period.
The number of crimes demonstrated a seasonal pattern, with peaks in the summer months and the fewest crimes in the winter months. This seasonal pattern remained consistent for all study years even though the total number of crimes decreased steadily.
The researchers also looked at deviations of daily temperatures from seasonal averages in trying to determine the effect of anomalies on crime rates. For example, during cool months, days that were 55 degrees warmer than the seasonal average were associated with 7 percent higher rates of disorderly conduct.