Complex sentence: The drought was set in motion by a La Nina which developed during 2005, which causes dry weather across much of the Southeast, this was evident due to the fact that winter 2005/2006 was dry for much of the region.
Split into simpler sentences: The drought was set in motion by a the weather phenomenon La Niña which developed during 2005. La Niña caused dry weather across much of the Southeast, this was evident due to the fact that winter 2005/2006 was dry for much of the region.