Why does it rain so hard and so heavily in strong convective weather?

Explain to you with physical knowledge that strong convection is actually a weather phenomenon caused by strong vertical movement of air. The most typical is the strong convective weather in summer afternoon: during the day, the ground constantly absorbs the short-wave radiation of the sun, and the temperature rises, releasing long-wave radiation to heat the atmosphere. When the air near the ground receives enough heat from the earth's surface, it will expand and reduce its density, and then the atmosphere will be in an unstable state.