Master of Science (MS)


Geography and Anthropology

Document Type



Tornadoes are a reoccurring severe weather hazard, with the highest rates globally occurring in the central United States. Despite their high frequency in the U.S., the scientific community’s disagreement of tornado activity during varying phases and intensities of the El Niño Southern Oscillation (ENSO) justifies a need for further research. In this study, tornado events from 1950 to 2014 in the U.S. east of the Rocky Mountains were investigated for seven phases of ENSO: strong, moderate, and weak El Niño/La Niña and the neutral phase. A seasonal Niño 3.4 index was used as the definition of ENSO. ENSO influences on tornado frequency, intensity, geographical distribution, and track area were tested using sophisticated mapping (i.e. GIS optimized hot spot analysis) and spatial statistics (i.e. average nearest neighbor and global Moran’s I). Results indicate that in spring, a Weak La Niña correlates with higher tornado intensity and stronger, long-lived tornadoes that shift eastward from the central U.S. as ENSO transitions from El Niño to La Niña. Summer has high tornado frequencies that do not vary dramatically across ENSO phases, with weak, short-lived tornadoes occurring in tornado outbreaks. Fall has similar tornado frequencies across six of the seven ENSO phases, apart from largely higher annual counts during a Strong La Niña phase. Winter exhibits more tornadoes that are stronger and longer-lived during a Moderate La Niña phase, with a northward expansion in tornado hot spots as ENSO transitions from El Niño to La Niña. In general, La Niña is most conducive for higher tornado counts and stronger, longer lived tornadoes.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Keim, Barry