Visualizing the Rise and Seasonality of Mass Shootings in the United States

Abstract

The authors visualize monthly mass-shooting incidents in the United States from 2013 to 2022 by integrating data from five major databases, each using different definitional boundaries. The combined dataset provides the most comprehensive view available of mass-shooting victimization during this period, including incidents often excluded in academic and media accounts. A tiled heat map and associated time-series plots reveal two key patterns: a clear rise in the frequency of mass shootings over time and increasingly pronounced seasonal clustering, with recent years showing concentrated summer peaks. These visualizations demonstrate how definitional choices shape interpretations of long-term trends and highlight the importance of inclusive, longitudinal approaches for understanding mass shootings as a persistent and evolving form of violence in the United States.

Discussions of mass shootings in the United States often rely on data from single sources or databases, each with its own criteria for inclusion and exclusion. This fragmented approach can obscure broader patterns, particularly as databases vary dramatically in how they define mass shootings, whether by number of victims, relationship between victims and perpetrators, or the inclusion of incidents involving gang, drug, domestic, or family violence (Bridges, Tober, and Brazzell 2023). To address this inconsistency, we integrate data from five major databases of mass shootings in the United States—Mother Jones, the Federal Bureau of Investigation (FBI) Supplementary Homicide Report, the FBI Active Shooter Report, Everytown for Gun Safety, and Gun Violence Archive—to produce a more comprehensive approximation of mass-shooting incidents from 2013 to 2022 (see Bridges et al. 2023 for database details). Although each source captures different events, combining them yields the least restrictive estimate of mass shooting frequency during the period. We focus on the period from 2013 to 2022 because these years allow consistent reconciliation across all five databases for a period covering a decade of incidents. This covers a recent decade spanning the coronavirus disease 2019 (COVID-19) pandemic and that offers sufficient data to reveal the twin trends we summarize here: long-term growth and emerging seasonal patterning in mass-shooting incidents.

The visualization (Figure 1) reveals two striking patterns: (1) a clear increase in mass shootings over time and (2) increasingly pronounced seasonal variation. The heat map and accompanying time-series plots show monthly incident counts between 2013 and 2022, along with a trend line chart and one with a smoothed five-year moving average. Although month-to-month variability exists, the overall trajectory is upward over time. Incidents rose sharply in mid-2020, coinciding with the early COVID-19 pandemic, a period marked by widespread social disruption, heightened stressors, and increased firearm purchasing (Hall 2025; Schleimer et al. 2021; Sun et al. 2022). Research suggests that pandemic-era increases in firearm violence may reflect multiple mechanisms, including potential increases in domestic violence (Schleimer et al. 2021) and gang-affiliated violence (Kim and Phillips 2021). Although our data do not show a disproportionate increase in domestic or neighborhood incidents relative to overall incidents, including them reveals their continued contribution to broader patterns of mass victimization, contexts often excluded from narrower definitions.

Figure 1.

Frequency of mass shootings per month in the United States, 2013 to 2022. Each tile in the heat map at the top of the figure represents a single month. The count refers to the number of mass shootings per month as a raw frequency. The two panels below the tiled heat map visualize the monthly counts in a line chart (top) and a five-year moving average smoothing short-term variability to highlight longer term trends. Data for the figure were produced by combining five separate databases reporting data on mass shootings in the United States over the period specified (Mother Jones’s U.S. Mass Shootings Database, the Federal Bureau of Investigation Supplementary Homicide Report, the Federal Bureau of Investigation Active Shooter Report, Everytown for Gun Safety, and Gun Violence Archive), removing duplicate incidents.

Seasonality appears to have intensified across the decade. Although early-period variation was more diffuse, recent years showed increasingly concentrated summer peaks, especially in June and July. Whether this shift reflects social rhythms, better data collection in the latter part of the period, or other structural dynamics remains an open empirical question, but its emergence underscores the importance of longitudinal and inclusive approaches to studying mass shootings.

Prior research has documented seasonal cycles in violent crime, with panel and time-series analyses showing summer peaks in assault and in some cases homicide (e.g., Hipp et al. 2004; McDowall and Curtis 2015; McDowall, Loftin, and Pate 2012). These cycles are generally interpreted through routine activities frameworks emphasizing seasonal shifts in social behavior and exposure to public space. Although this literature focuses on interpersonal or property crime rather than mass shootings, it highlights how violence is embedded in recurring social and temporal structures. Our visualization suggests that mass shootings increasingly follow similar seasonal rhythms, indicating that this form of violence may also be shaped by seasonal social processes. Unlike prior work, which treats seasonality as a stable feature of violent crime, our visualization suggests that mass shootings became seasonal from 2013 to 2022, with concentrated summer peaks emerging only in more recent years. Whether this reflects changing social rhythms, improved data collection, shifts in public space use, or other structural processes remains a question.

To integrate the five databases, we adopted a maximally inclusive approach: any incident appearing in at least one source was retained, and duplicate events across datasets were removed. No additional filtering criteria were applied. Because the five databases vary in their definitional boundaries (e.g., number of victims, inclusion of nonfatal injuries, and whether domestic, felony-related, or gang-affiliated and drug-related incidents are counted), this procedure yields a least restrictive estimate of monthly mass-shooting incidents. Our goal in this visualization is not to adjudicate among definitions but to illustrate the broadest temporal patterns that emerge when definitional boundaries are widened. For detailed discussion of the definitional and methodological issues associated with integrating these data sources, see Bridges et al. (2023).

This visualization draws on data through 2022, a period for which all five databases were carefully reconciled. Preliminary analysis of subsequent years (2023–2025) conducted as part of a larger project does not appear to be at odds with the patterns identified here, including the rise in incident frequency and the emergence of summer clustering. This suggests that the results presented in this visualization are representative of recent trends while focusing on one decade of harmonized data.

The intensification of seasonal clustering over this decade points to mass shootings as a patterned social phenomenon rather than a series of isolated or random events. Seasonal concentration suggests the relevance of social rhythms that organize everyday life, including things such as school calendars, patterns of work and leisure, the use of public space, and institutional cycles of surveillance and regulation associated with seasonal openings and closures of parks, pools, festivals, and other large social gatherings. Although the present visualization cannot adjudicate among these mechanisms, it highlights how mass-shooting incidents are embedded in recurring temporal structures that shape opportunities for mass violence of this type. Importantly, these patterns become most visible when definitional boundaries are expanded to include incidents often excluded from narrower operationalizations of incidents. By retaining these events, the visualization underscores how routine and extraordinary forms of mass victimization are interwoven, revealing regularities more easily obscured when mass shootings are defined in ways that present them as rare, making identifying the social patterns structuring them harder to see.

This visualization provides the broadest available picture of monthly mass-shooting patterns in the United States from 2013 to 2022. It highlights the concurrent rise in incident frequency and the intensification of seasonal clustering, raising important questions about the social processes driving these shifts.

Supplemental Material

sj-docx-1-srd-10.1177_23780231261425279 – Supplemental material for Visualizing the Rise and Seasonality of Mass Shootings in the United States

Supplemental material, sj-docx-1-srd-10.1177_23780231261425279 for Visualizing the Rise and Seasonality of Mass Shootings in the United States by Tristan Bridges, Tara Leigh Tober, Sara Tyberg and Liz M. Munday in Socius