Here's why this happens:
* Saturated Soil: If the ground is already full of water (saturated), it can't absorb any more.
* Impermeable Surfaces: Paved areas like roads, sidewalks, and parking lots prevent water from infiltrating the ground.
* Steep Slopes: Water flows downhill more quickly on steep slopes, leaving less time for it to soak in.
* Frozen Ground: Frozen soil is impermeable, preventing water from entering.
* High Intensity Rainfall: Heavy rain falls too fast for the ground to absorb it all.
Runoff is a key part of the water cycle and can have both positive and negative impacts:
* Positive: It replenishes rivers, lakes, and oceans, and can be used for irrigation.
* Negative: It can cause erosion, flooding, and pollution by carrying pollutants into waterways.
