What does it mean to rain in long summer?

If it rains heavily in the long summer solar term, no matter how heavy or small it is, it will only rain, which indicates that there will be more rain in the future.

This is an agricultural proverb used by the ancients to predict the rainfall behind the long summer solar terms. In some places, there is a saying that it will rain and flood in summer, which means the same thing. That is to say, it rains in the long summer solar terms, and there is plenty of rain behind it.