If an area of the ground is paved over with asphalt, the amount of runoff that occurs after a rain storm in this region would likely decrease.
Asphalt has a very low permeability for water, which means that it does not allow water to pass through it easily. When rain falls on an area that is paved with asphalt, the water is not able to infiltrate into the ground, and instead it runs off the surface of the asphalt and into the stormwater drainage system. This can lead to a reduction in the amount of runoff that occurs in the region.
In contrast, if the ground is not paved with asphalt and is instead covered with soil or other materials that have higher permeability for water, more of the rainwater will be able to infiltrate into the ground, which can lead to an increase in the amount of runoff that occurs in the region.
Overall, the permeability of the ground can significantly affect the amount of runoff that occurs after a rain storm, and paving the ground with asphalt can reduce the amount of runoff that occurs in the region.