Researchers have noted that fires appear in cycles associated with those of the hydroperiods.[3] The first cycle is the annual wet-season fires that occur with rapid frequency during the summer, but are quickly extinguished. Dry-season fires are rarer due to the lack of lightning, but their damage may be more pervasive.[20] A longer fire cycle spanning ten to fourteen years coincides with similar water cycles affected by global climate conditions. Fires in this cycle may be numerous and have little effect, or rare and have catastrophic consequences. The third cycle appears in a 550-year frequency associated with severe drought. Layers of charcoal have been detected inside peat in parts of the Everglades, indicating the region endured severe fires for years at a time, although this trend seems to have abated since the last occurrence around 940 BCE.[3]