5.2c

• how do humans disrupt processes in drainage basins?

  • deforestation
  • land use change
  • water storage reservoirs
  • water abstraction
• deforestation?

  • reduces the amount of water that is intercepted by vegetation = increases the amount that reaches the surface therefore increases direct runoff
  • in forested areas, dead plant material on the forest floor helps retain water, allowing it to infiltrate the soil rather than run off. when this is removed, less infiltration occurs
  • soil erosion is more likely to occur on exposed land, reducing the soil's ability to store water, as there's limited infiltration, groundwater levels decline and the water table drops
• land use change?

  • agriculture --> growing crops increases infiltration, however, heavy machinery compacts the soil, decreasing its permeability and therefore decreasing infiltration and increasing direct runoff = flooding is more likely
  • urbanisation = impermeable surfaces prevent infiltration + roof-top guttering and road drains decrease lag time and increase discharge
• water storage reservoirs?

  • creating new storage reservoirs by building dams increases the amount of freshwater that humans can access
  • reduces the level of channel flow (river discharge) into oceans = increases surface storage + creates large areas of standing water increases the level of evaporation that can happen there
• water abstraction?

  • more water is abstracted (taken from stores) to meet demand in areas of high population density --> reduces the amount of water in stores such as lakes, rivers, reservoirs and groundwater
  • during dry seasons even more water is abstracted (especially groundwater and from reservoirs) for consumption and irrigation, depleting stores further
  • in some places, humans abstract water from aquifers - occurs at a faster rate than the aquifer is recharged
• what is irrigation?

  watering crops artifically
• why is there very high rainfall in the Amazon?

  there's lots of evaporation over the Atlantic Ocean and moist air is blown towards the Amazon + warm temperatures = high evapotranspiration rates = increases amount of local convectional precipitation
• how have humans disrupted the hydrological cycle in the Amazon?

  • deforestation e.g. to harvest timber or to use the land for farming = no tree canopy to intercept rainfall = increases amount of water reaching the ground and there's too much water to infiltrate into the soil so water moves to rivers as saturated overland flow = increases the risk of flooding
  • deforestation also reduces the rate of evapotranspiration = less water vapour reaches the atmosphere = fewer clouds form and precipitation is reduced = increases risk of drought