Short-term high temperature may increase the incidence risk of collective conflicts: A case-crossover study in the Greater Middle East.

BACKGROUND:Violent conflict is a formidable global challenge, with long-lasting impacts on individual health and society security. There has been compelling evidence that heat can increase aggression intention on the individual level. However, little is known about the short-term relationship between ambient temperature and collective violent conflicts, especially in less developed regions. METHOD:We conducted a time-stratified case-crossover study combined with the distributed lag nonlinear model (DLNM) among 247,773 violent conflicts from 29 countries or regions in the Greater Middle East, between 1997 and 2021. Potential modification effects of economic status and climate conditions were explored by stratified analyses. Negative control and sensitivity analyses were also performed to test the robustness of our model. RESULTS:We observed significant associations between higher temperature and the onset of five categories of violent conflicts. The effects generally occurred within the first several days after exposure. The incidence risks of battles, violence against civilians, explosions/remote violence, protests and riots were 1.60 [95 % confidence interval (CI): 1.31-1.95], 1.82 (95 % CI: 1.37-2.42), 1.24 (95 % CI: 1.08-1.41), 1.16 (95 % CI: 1.09-1.24) and 1.54 (95 % CI: 1.22-1.95) when comparing extreme high temperatures to minimum-risk temperatures. The associations were generally more prominent in areas with lower economic levels and associations in regions of the continental climate are also stronger. CONCLUSIONS:Our finding reveals novel and concrete evidence that short-term high temperature could increase the risk of multiple forms of violent conflict in the Greater Middle East and provides new insights into the potential short-term mechanisms under the heat-collective violence association.