INTRODUCTION: Over the past 30 years, south-central Somalia, Puntland (north-east) and Somaliland (north-west) have experienced recurring drought- and conflict-related crises. By the end of 2018, the number of internally displaced persons (IDPs) in the region had reached 2.6 million; most were displaced to larger towns under government control, where humanitarian assistance was more accessible. Understanding the drivers of crisis-related displacement can provide insight into how responses can best manage and respond to displacement to prevent downstream morbidity and mortality. We aimed to explore the temporal patterns and crisis-related risk factors for population displacement in Somalia from 2016 to 2018, a period of severe drought. METHODS: We conducted an ecological study of secondary panel data stratified by district and month. The study population included all people in the region from 2016 to 2018. The outcome was defined as the number of new out-migrating internally displaced persons (IDPs) per district-month. Exposure variables included armed conflict, rainfall, food insecurity and food security services. Lags at one, two and three months were generated to explore possible delayed effects. All univariate and multivariate analyses were conducted using negative binomial regression models with mixed effects incorporating the district as a random effect. RESULTS: From 2016 to 2018, the proportion of IDPs increased from 9% to 25% in Somalia, Puntland and Somaliland. We observed strong associations between IDP out-migration rate and failed rains at a three-month lag, food insecurity at a one-month lag, and the presence of therapeutic food services with no lag. IDP out-migration rate was not associated with armed conflict intensity, and cash- and rations-based food security services. DISCUSSION: This study identified temporal, and socially and biologically plausible associations between key crisis-related risk factors and displacement in Somalia. The findings suggest a sequence of events spanning a few months, where failed rains and consequent food insecurity likely prompted early population out-migration to larger urban centers where humanitarian services were more accessible. The presence of therapeutics-based food security services could represent a more general correlate of crisis severity and the decision to migrate.