The stream continues to flow after it has stopped raining because the water that is flowing in the stream is not just from the immediate precipitation, but also from the water that has been collected and stored in the watershed. The watershed is the area of land that drains water into a stream, river, lake or other body of water.
Water that falls as precipitation on the watershed can be stored in the soil, in rock crevices, or in surface depressions such as ponds or lakes. Some of the water may also be taken up by plants, and some may evaporate back into the atmosphere. However, much of the water will eventually make its way to the stream through a variety of processes such as infiltration, surface runoff and subsurface flow.
Additionally, streams and rivers often receive water from a variety of sources such as tributaries, underground aquifers, and melting snow and ice. These sources can help to keep the stream flowing even after it has stopped raining.
In summary, the stream continues to flow after it has stopped raining because the water that is flowing in the stream is not just from the immediate precipitation, but also from the water that has been collected and stored in the watershed, and also from other sources that feed into the stream.