When rain falls on land, what factors influence the amount of water that soaks in?
The dampness of the ground, the type of ground and the surrounding environmental factors.
If there has been heavy rain during the last time period the soil would have lost most of its ability to absorb water due to its excess in it.
If the ground is rocky or there are rocks under a rather thin layer of soil there won't be enough soil to absorb the water. A combination of the above may influence the amount of soaking water even more.