The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes (not rivers, deltas, or marine habitats). Rainfall was seasonal, alternating between semi-arid, and mesic conditions. The climate was temperate. The Jehol ecosystem was interrupted at times by ash eruptions from volcanoes to the west. The word "Jehol" was the name given during the Japanese occupation of North-East China, 1933–1946.