Human influence on hydrological processes

1. Withdrawals: We take water out of the system to irrigate crops, to provide us with drinking water and to carry out many of our industrial processes.
2. Discharges: precipitation carries pollutants like farm pesticides, herbicides and fertilizers as well as wastes from faulty septic systems and improperly handled manure in water sources. In urban areas, the pollutants may include gas, oil, pet waste, fertilizers, pesticides, salt and treated human waste from sewage treatment plants
3. Production of GHGs
4. Deforestation: Cutting down trees increases run-off, decreases evapotranspiration (and therefore cloud formation) and leads to more extreme river flows as water is not intercepted and stored by the trees.
5. Urbanization: The removal of natural vegetation and replacement with impermeable surfaces and drains can speed up overland flow and evaporation and can lead to higher river levels. It also decreases the amount of water which returns to groundwater storage, possibly reducing the water table.
6. Mining: Breaking up of rocks leads to increased silting up of lakes, rivers and reservoirs leading to reduced storage capacity in these areas. Mining may also lead to reduced vegetation cover leading to increased run-off.
7. Dam building: Greatly reduces the discharge of a river as storage is increased. Leads to increased evaporation and therefore can alter rainfall patterns.