Complex sentence: The 2007 Mozambican flood began in late December, 2006, when the Cahora Bassa Dam overflowed from heavy rains on Southern Africa and worsened in February, 2007, when the Zambezi River broke its banks flooding surrounding areas in Mozambique.
Split into simpler sentences: The 2007 Mozambican flood began in late December 2006 when the Cahora Bassa Dam overflowed from heavy rains on Southern Africa. It worsened in February 2007 when the Zambezi River broke its banks, flooding the surrounding areas in Mozambique.