The diagram illustrates the water cycle in both forested and urban areas.
Overall, both areas initially receive precipitation. The water cycle in the forested area proceeds without any obstruction, whereas the urban area encounters several obstacles throughout the water cycle, resulting in polluted runoff and increased erosion.
In the forested area, water evaporates from the soil and returns to the atmosphere, while infiltration occurs after rainfall, as water moves from the permeable topsoil into the less-permeable subsoil above the rock. When infiltrating water reaches the water table, it contributes to the baseflow, which eventually flows into the stream. Both baseflow and surface runoff contribute to the stream. Trees also release water vapour through their leaves, a process known as transpiration.
In the urban area, infiltration is reduced because much of the ground is covered by impermeable surfaces such as roads and buildings. As a result, less water reaches the groundwater, leading to a reduction in baseflow. Instead, a greater proportion of rainfall becomes surface runoff, which can carry pollutants into streams. The increased surface runoff also contributes to greater erosion. In addition, evaporation and transpiration are lower than in the forested area.