The ruins are on lowland rainforest, but Tikal had no water other than what was collected from rainwater and stored underground. Archaeologists working in Tikal during the last century used the underground facilities to store water for their own use. The absence of springs, rivers, and lakes nearby is unusual for a major city. However, Tikal did well with agricultural techniques. These were more advanced than the slash & burn methods originally theorized by archeologists. The reliance on seasonal rainfall made Tikal open to drought. This is now thought to play a major part in the "Classic Maya Collapse".