Hydrosphere

• Hydrosphere


  The water found on, under, and above the Earth's surface
• Water is a renewable resource that is essential for all living organisms
• Human society has only been able to develop easily where water is available
• Water is often unevenly distributed and human activities affect the quantity and quality of the water that is available
• Developing strategies to ensure adequate future supplies of water requires an understanding of human uses of water, how these are changing, the natural processes that cycle water in the environment and how human activities affect these
• Global demand for water

  • Agriculture (70%)
  • Industry (22%)
  • Domestic uses (8%)
• Selected major water use activities

  • Irrigation
  • Cooling
  • Heating
  • Washing
  • Solvent
  • Flushing toilets
  • Washing clothes, dishes
  • Hygiene
• Reasons for increasing global demand for water

  • Increase in population
  • Increase in per-capita use with increased affluence
  • Increased irrigation of farmland
  • Industrialisation
• The global demand for water is increasing for a range of reasons
• Increase in population


  The population may grow because the birth rate is higher than the death rate or because of immigration. Migrants may move from other countries or within a country.
• Increase in per-capita use with increased affluence


  In the poorest communities where there is no piped supply, domestic water use may be limited to the amount that can be carried from the source which may be the nearest river. As piped water becomes available and people become increasingly affluent, they buy more appliances that use water such as washing machines, dishwashers and swimming pools. Although modern appliances may be designed to use less water, there is still a link between affluence and water consumption.
• Increased irrigation of farmland

  As commercial agriculture expands, the increased income allows money to be invested in irrigation schemes. Irrigation uses more water than all other human uses combined. Subsistence agriculture usually relies on the water that is naturally available, adapting the type of farming if water is a problem, for example nomadic herding rather than arable farming. As affluence increases and energy and equipment become available, irrigation can increase, pumping water from aquifers and rivers or storing it in a reservoir.
• Industrialisation


  Different industries have different water requirements. Heavy industry, such as the chemical and steel industries or paper making, use much more water than lighter manufacturing industries. The service industries use very little water apart from the water used by the workers for domestic uses.
• Quantity of water in different reservoirs

  • Oceans (97%)
  • Land ice (2%)
  • Groundwater (0.7%)
  • Lakes and rivers (0.01%)
  • Soil moisture (0.005%)
  • Atmosphere (0.001%)
  • Living organisms (0.00004%)
• Residence time of water in different reservoirs

  • Oceans (up to 4000 years)
  • Groundwater (100-10000 years)
  • Lakes and rivers (20-100 years)
  • Soil moisture (2 months-100 years)
  • Atmosphere (2 months)
  • Living organisms (10 days)
• The importance of a reservoir of water cannot be predicted from its quantity. Some reservoirs are abundant but are transferred slowly, for example, groundwater, others have a small total quantity but are transferred quickly, for example, atmospheric water.
• Residence Time


  Volume of water in the reservoir/mean transfer rate
• Some abstraction of river water has little impact on the river as the used water is cleaned and returned to the river. However, rivers have often been used to carry away wastes.
• Some abstractive uses do not return the water to the river which reduces downstream flow, for example, agricultural irrigation.
• Surplus river water is often stored in reservoirs for use later.
• Environmental effects of reservoirs

  • Habitat change
  • Barrier to wildlife migration
  • Changes to river regime downstream
  • Sedimentation
  • Microclimates
• The abstraction of river water often reduces downstream flow. This affects the river and any lakes that it feeds. Some rivers completely cease to flow.
• Aquifer


  A body of rock that holds water which is exploited as a resource
• Features required for a rock to form an aquifer

  • Porosity
  • Permeability
  • Associated geological structures
• Porosity


  A measure of the proportion of a rock's volume that is space and could therefore hold water
• Permeability


  A measure of the ease with which fluids may flow through a rock because of the interconnections between the spaces and their size
• Associated geological structures


  The rock below the water bearing rock must be impermeable to prevent the escape of the water. Some of the rock above must be permeable to allow recharge of the aquifer.
• The natural amount of water in an aquifer is in a state of dynamic equilibrium of the natural inflow or recharge of water into the aquifer and the water that flows out of the aquifer.
• If abstraction of water by humans is greater than the rate of recharge, then the volume of water in the aquifer will decline.
• Most aquifer recharge takes place as precipitation landing on the ground surface infiltrates and percolates through soil and rock to the aquifer.
• Some aquifers were recharged during the last ice age 10-20,000 years ago when the global climate was wetter. Many of these are not currently being recharged so their exploitation will eventually lead to shortages.
• Effects of over-exploitation of aquifers


  • Changes in surface hydrology
  • Ecological impacts
  • Salt water incursion
  • Subsidence
  • Reduced supplies
• Nearly half the world's population live in countries that are over-exploiting their aquifers.
• The availability of water has a major effect on many aspects of life. It influences where people can live, what they can eat, which industries can be developed, and quality of life.
• To satisfy the growing population and increased per-capita demand, it may be necessary to exploit previously unused resources or increase the exploitation rate of existing supplies.
• Rainwater collection


  Increasingly important in areas where public supplies cannot match consumer demand, for example, many cities in India. It also reduces urban flooding after heavy rain. Collecting rainwater is also important in rural areas where there is no public water supply. The water is often cleaner than other sources such as rivers.
• Rivers


  Often the most convenient source of water. Being long, they are accessible over a large land area. Natural contaminants are rarely a serious problem and human problems were not usually a problem until population density rose to the point where waste from a community upstream did not break down before it reached the next community.
• Reservoirs


  Allow the storage of water from times when there is a surplus of water so that it can be used when there is a shortage. But, even if there is a suitable water supply, many other factors must be considered when choosing a site for a dam and reservoir.
• Reservoir construction


  • Main cost is building the dam
  • Income comes from the amount of water it can provide
• Ideal topography for reservoir

  • Narrow exit from a large deep basin
  • Relatively small dam can hold back a huge volume of water