Nature Communications 6: Article number:6599 (2015); Published 25 March 2015; Updated 5 June 2015.

The captions of Figs 2 and 3 of this Article contain typographical errors that were introduced during the production process. In both Figs 2 and 3, the units for the tornado occurrences should be 10,000 km2·yr−1 rather than 100 km2·yr−1.