Physical Factors Affecting Water Supply

Drainage density: The density of rivers and streams in each area.

Discharge: The rate of water flow in a river.

Impermeable: Rock or soil which will not transmit water.

River regime: The variation in annual river discharge.

Aquifer: underground porous rock which will hold groundwater and let it through.


  • The distribution of water globally is related to the Earth’s climatic zones.
  • Regions near to the equator receive high levels of annual precipitation, while some tropical areas suffer recurring drought (HADLEY CELL/ITCZ).
  • Rainfall may also vary with the seasons.
  • Equatorial areas such as Amazon lowlands have two distinct periods of wet weather per year.
  • High mountainous with snowpack hold vast reserves of water, some of which is released in late spring and during the summer.



  • Where the rocks underlying a river basin are impermeable, water will remain on the surface as runoff, creating a high drainage density.
  • Permeable soils and rocks such as limestone may allow water to pass into underground drainage systems.
  • Aquifers such as chalk and porous sandstones can store vast quantities of water underground.



  • World’s major rivers store large quantities of water and transfer it across the continents.
  • River flows generally increases downstream as tributaries feed into the main river, though high temperatures can lead to considerable water loss by evaporation.
  • Seasonal changes in climate can also create significant variations in discharge and produce distinctive river regimes.