Unit 3.8 Water-Hydrological Cycle and Over-exploitation of surface and groundwater

Why Water is a Resource ?

1) It is important because it is needed for life to exist.

2) Many uses of water include agricultural, industrial, household, recreational and environmental activities.Virtually all of these human uses require fresh water.

3) Only 2.5% of water on the Earth is fresh water, and over two thirds of this is frozen in glaciers and polar ice caps.

4) Water demand already exceeds supply in many parts of the world, and many more areas are expected to experience this imbalance in the near future.

5) It is estimated that 70% of world-wide water use is for irrigation in agriculture.

6) Climate change will have significant impacts on water resources around the world because of the close connections between the climate and hydrologic cycle.

7) Due to the expanding human population competition for water is growing such that many of the worlds major aquifers are becoming depleted.

8) Many pollutants threaten water supplies, but the most widespread, especially in underdeveloped countries, is the discharge of raw sewage into natural waters.

Hydrological Cycle:

(Image Source: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/smry.rxml)

The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation.

Once the water reaches the ground, one of two processes may occur;

(1) some of the water may evaporate back into the atmosphere or

(2) the water may penetrate the surface and become groundwater.

Groundwater either seeps its way to into the oceans, rivers, and streams, or is released back into the atmosphere through transpiration. The balance of water that remains on the earth’s surface is runoff, which empties into lakes, rivers and streams and is carried back to the oceans, where the cycle begins again.

Over Exploitation of Surface Water:

Surface water is mainly used in all human’s agricultural, industrial, household, recreational and environmental activities, due to which its quality and quantity both degrades. Since lakes, ponds, rivers, sea are used for dumping industrial and sewage wastes, dead bodies, solid wastes etc. hence their quality degrades, which give rise to many environmental, ecological and health problems.

The major reasons for the over-exploitation and over-utilization of surface water resource are:

(i) Population growth:

In 2000, the world population was 6.2 billion. The UN estimates that by 2050 there will be an additional 3.5 billion people with most of the growth in developing countries that already suffer water stress. Thus, water demand will increase unless there are corresponding increases in water conservation and recycling of this vital resource.

(ii) Expansion of business activity:

Business activity ranging from industrialization to services such as tourism and entertainment continues to expand rapidly. This expansion requires increased water services including both supply and sanitation, which can lead to more pressure on water resources and natural ecosystems.

(iii) Rapid urbanization:

The trend towards urbanization is accelerating. Small private wells and septic tanks that work well in low-density communities are not feasible within high-density urban areas. Urbanization requires significant investment in water infrastructure in order to deliver water to individuals and to process the concentrations of wastewater – both from individuals and from business. These polluted and contaminated waters must be treated or they pose unacceptable public health risks.

(iv) Climate change:

Climate change could have significant impacts on water resources around the world because of the close connections between the climate and hydrological cycle. Rising temperatures will increase evaporation and lead to increases in precipitation, though there will be regional variations in rainfall.

Overall, the global supply of freshwater will increase. Both droughts and floods may become more frequent in different regions at different times, and dramatic changes in snowfall and snow melt are expected in mountainous areas.

Higher temperatures will also affect water quality in ways that are not well understood. Possible impacts include increased eutrophication. Climate change could also mean an increase in demand for farm irrigation, garden sprinklers, and perhaps even swimming pools.

(v) Pollution:

Water pollution is one of the main concerns of the world today. The governments of numerous countries have striven to find solutions to reduce this problem. Many pollutants threaten water supplies, but the most widespread, especially in developing countries, is the discharge of raw sewage into natural waters; this method of sewage disposal is the most common method in underdeveloped countries, but also is prevalent in quasi-developed countries such as China, India and Iran.

In addition to sewage, nonpoint source pollution such as agricultural runoff is a significant source of pollution in some parts of the world, along with urban storm water runoff and chemical wastes dumped by industries and governments.

Over Exploitation of Ground Water:

(i) Subsidence:

When groundwater withdrawal is more than its recharge rate, the sediments in the aquifer get compacted, a phenomenon known as ground subsidence. Huge economic losses may occur due to this phenomenon because it results in the sinking of overlying land surface. The common problems associated with it include structural damage in buildings, fracture in pipes, reversing the flow of sewers and canals and tidal flooding.

(ii) Lowering of water table:

Mining of groundwater is done extensively in arid and semi-arid regions for irrigating crop fields. However, it is not advisable to do excessive mining as it would cause a sharp decline in future agricultural production, due to lowering of water table.

(iii) Water logging:

When excessive irrigation is done with brackish water it raises the water table gradually leading to water logging and salinity problems.