David Krohn

Man’s impact on the hydrological cycle

Human activities have had significant impacts on the hydrological cycle, both on the quantity and quality of water flowing within it. A common problem is the overuse of watercourses resulting in drastically reduced flow through rivers into natural stores. A good example of this is the situation in the Aral sea basin, where over extraction for irrigation has resulted in the cessation of inflow from contributing rivers. Diversion of water for irrigation purposes modifies natural hydrological processes and irrigated land often has high rates of evaporation and evaporation. Another common problem is the over regulation of river basins as dams, levees and barrages aim to accumulate water for human consumption or protect urban areas. However, they increase evaporation, and raise the water table through increased percolation. Gradual changes occur due to the decreased freedom of sediment flow, which can affect flow velocities and river development.

There are also large problems attached to alterations in the water table. A rise in the level of groundwater can saturate topsoils or lead to salinization. Artificial drainage is often a manmade solution to this problem as the return of hydraulic action increases flow velocities but can lead to a decrease in evapotranspiration. In addition, over extraction of water from aquifers can lead to dangerously decreased water levels.

Changing the land use of river basins also has marked effects on transfers of water as evaporation and flow characteristics are altered. This is especially clear in urbanized areas where infiltration is all but halted and evapotranspiration is greatly reduced. Urbanization also leads to increased flood risks and large surface flows.

Deforestation and overexploitation of vegetation may be to blame for increased drought risks and increased flooding as good vegetation cover helps regulate, store and absorb water flows. Another consequence of deforestation is decreased transpiration and infiltration as vegetation cover is reduced. Changes in precipitation interception and infiltration increase flood risks and affects the amount of water penetrating to groundwater stores.

Resources:

LS Kuchment ‘WATER RESOURCES MANAGEMENT – The Hydrological Cycle and Human Impact on it’ available at http://www.eolss.net/ebooks/Sample Chapters/C07/E2-16-10-01.pdf(accessed Feb 2009)

Trinity College ‘The Water Cycle: hydrological cycle and human impact’ available at http://www.trinity.wa.edu.au/plduffyrc/subjects/sose/geography/respop/watcycle.htm(accessed Feb 2009)

Tags: change in land use, hydrological cycle, man's impact on the hydrological cycle