Final answer:
The Zambezi River's frequent flooding in southeast Africa is primarily caused by heavy rainfall in the region.
Step-by-step explanation:
The main cause of the Zambezi River's frequent flooding in southeast Africa is heavy rainfall in the region. The river flows through several countries before reaching the Indian Ocean, and its basin receives rain from both the Indian Ocean monsoon system and localized rainfall. This heavy rainfall, especially during the rainy season, can result in the river exceeding its banks and flooding the adjacent land. While high tide, dam failures, and melting glaciers could affect other rivers, they are not the primary factors for the Zambezi's flooding. The Zambezi is located in a region with minimal glacier coverage, and though dam infrastructure can impact river flow, it is the substantial precipitation rates that lead to its frequent floods.