Complex sentence: In June 2001, Tropical Storm Allison dumped up to of rain on parts of Houston, causing the worst flooding in the city's history; the storm cost billions of dollars in damage and killed 20 people in Texas.
Split into simpler sentences: In June 2001, Tropical Storm Allison dumped up to of rain on parts of Houston, causing the worst flooding in the city's history. The storm cost billions of dollars in damage and killed 20 people in Texas.