Changes in the water cycle over time - Human impacts Flashcards
Where does 40% of all global deforestation occur?
The Amazon Rainforest Basin
Why is there so much deforestation in the Amazon Rainforest?
- 10% lots to cattle and agriculture farming
- Mining
- Soybean farming
What is forest degradation?
The fragmentation of the forest which disrupts the quality of the environment and causes a loss in biodiversity.
What are the local impacts of deforestation on the water cycle?
Following deforestation
1. evapotranspiration is lower because the replacement vegetation has smaller leaves and roots, reducing infiltration rates
2. Overland flow and throughflow occur due to the lack of vegetation
3. Surface runoff leads to increased river discharge and flashiness, causing localised flooding.
What are the local impacts of extensive deforestation on the water cycle?
Following deforestation:
1. Since evapotranspiration is low, most of the water leaves the area via channel flow, meaning there is less water vapour available in the atmosphere for precipitation.
2. If precipitation levels fall, less water gets to the river channel so the flow is reduced, causing a positive feedback.
What are the impacts of urbanisation on the water cycle?
- Impermeable surfaces (concrete) prevent precipitation from being absorbed, causing increased surface runoff
- Impermeable surfaces (concrete) prevent soil infiltration and reduces the the volume of water able to percolate into underground acquifers.
- More water is trapped on the surface in soil storage and more exposed to heat, causing increased evaporation.
What is the urban island effect?
A localised warming that occurs in cities where man-made materials absorb and retain heat better than natural surfaces.
Why is the urban island effect important?
- it is projected that in 2050, 68% of the world’s population will live in urban areas.
What is subsurface drainage?
- Subsurface drainage occurs through a network of perforated tubes, installed 60-120cm below the soil surface to lower the depth of the water table. These tubes allow excess water to leave the field through small cracks in them.
What are the negative impacts of subsurface drainage (soil drainage for farming) on the water cycle?
- Increases the speed of throughflow in the soil, increasing river discharge and risk of flooding
- Can lead to eutrophication and disturb the balance of organisms present in the water - algal growth reduces water quality.
- The dry topsoil can be subject to wind erosion
What are the benefits of farming on the water cycle?
- Improved aeration of the soil means microorganisms have better conditions to thrive, allowing nutrients to break down quicker
- The build up of an improved soil structure allows roots to grow longer and faster.
- Heavy machinery can work on the land without compacting it
How are water bunds used in farming as an alternative to subsystem drainage?
Water bunds have been used to reduce runoff and increase infiltration in Kenya as a method of drought restoration. Overtime, this allows vegetation to grow, increasing evapotranspiration and precipitation.
What are the main reasons for the over abstraction of groundwater?
- Low rainfall
- High population density
- Intensive agriculture (irrigation) or industrial activity
Describe the water cycle in the chalk of Southern England.
The water within the chalk acquifers is replenished by rainfall that lands on the chalk hills of the North and South Downs and the Chilterns. Up to 95% of the flow in chalk stream systems is derived from underground acquifers.
How has water abstraction in the chalk of Southern England impacted the water cycle?
Abstraction for public consumption has dramatically reduced the flow in many chalk streams and dried up many areas during summer and spring.
