Water Cycle Pack A

Question 1

What three things greatly impact the water cycle?

Answer 1

• Population growth
• Increased affluence
• Climate change

Question 2

What are the main uses of water?

Answer 2

• Domestic
• Agriculture
• Industry

Question 3

In what general ways can humans affect the water cycle?

Answer 3

• Directly by taking water away from stores or flows, transferring water from one place to another or adding water to certain places
• Indirectly through building urban areas or changing land uses from vegetation

Question 4

What makes the water cycle a system?

Answer 4

It has inputs, outputs, processes, stores, equilibrium, feedback and tipping points

Question 5

How does a simple drainage basin work?

Answer 5

• Major input is precipitation
• Flows include infiltration, throughflow and percolation
• Major outputs include transpiration and evaporation
• Stores include vegetation, groundwater storage, surface storage and river channels

Question 6

How have humans changed precipitation?

Answer 6

• Cloud seeding in Boise, Idaho
• Particulates (often silver iodine) are release into the atmosphere
• Act as the hygroscopic nuclei that are required for rain and snow to occur as water vapour accumulates the particulates until they are heavy enough to fall
• Experiment was called SNOWIE
• Local farmer’s relied on melting snow from mountains as a water supply for irrigation but the increasing demand for water put pressure on existing stores
• Enlarges the snowpack during winter

Question 7

How have humans changed interception?

Answer 7

• Deforestation in Freetown, Sierra Leone
• 1,141 people were dead or missing after a mudslide in August 2017
• The result of a particularly intense rainy season
• The city has grown so the city limits have crept up onto the surrounding hills
• The Central Highlands have been deforested to leave exposed and weakened soil
• Infiltration rates decrease and direct overland flow increases without the vegetation to intercept rainfall
• There are shorter lag times and flooding
• There are no roots to stabilise the soil, increasing the chances of mudslides

Question 8

How have humans changed overland flow?

Answer 8

• Natural flood management in Pickering, Yorkshire
• Scheme called Slowing the Flow uses natural processes and features to manage river discharge
• Constructed low-level bunds (soil embankments)
• Planted more trees, especially along stream sides and in foodplain
• Restored woody debris dams and wetlands
• Increases interception and infiltration in upper parts of drainage
• Increases water storage in tributaries and improves river flow
• Holistic approach which is more sustainable

Question 9

How have humans changed infiltration and aquifers?

Answer 9

• Houston, Texas
• Population has doubled to 2.3 million people in the last fifty years
• The physical limits of the city have been pushed outwards leading to the loss of 100,000ha of wetland and the building of over 7,000 homes on floodplains
• Increased abstraction from 3 main aquifers below the city has lead to 10-25mm subsidence per year
• Hurricane Harvey in August 2017 was recorded as the wettest tropical cyclone to every hit the USA
• Areas received 400mm of precipitation in 1 day
• Suffered substantial flooding (as no wetlands and full foodplain)
• Warming climate led to more rainfall events as warmer air can hold more moisture before it becomes saturated
• Local anthropogenic warming can lead to conventional uplift and increased rainfall

Question 10

How have humans changed vegetation storage?

Answer 10

• County Leitrim, North of Ireland
• Only had 1% forest cover in 1900 and now has 11% cover, aiming to reach target of 18%
• Sitka spruce was planted which is a large, evergreen, coniferous tree and is effective at capturing carbon
• Have stiff, sharp, acidic needles which do not decompose in the same way as deciduous trees
• Has shallow roots which provide fewer channels through which water can infiltrate
• Decreased infiltration rates under Sitka forests lead to increased overland flooding and the likelihood of river floods

Question 11

How have humans altered surface storage, river flow and evaporation?

Answer 11

• Grand Ethiopian Renaissance Dam, Nile
• Construction began in April 2011 and the process of filling the reservoir began in July 2020
• All hydroelectricity will feed into the national grid of Ethiopia and surplus electricity from during rainy seasons will be exported to Sudan
• 65 million Ethiopians will benefit from a regular supply of electricity
• There is an increase in evaporation rates, reduction in discharge downstream and a rise in the surrounding water table
• There are lower levels of evaporation compared to the Aswan Dam in Egypt
• Contentious from the outset as both Sudan and Egypt were worried about impacts to its farmers and local ecology
• Ethiopia says it will alleviate potential flooding in those countries and prevent silt reaching downstream

Question 12

How have humans changed groundwater storage?

Answer 12

• Ogallala Aquifer is 1 of the largest in the world
• Covers approximately 450,000 sq km that underlies 8 states (e.g. Colorado, Kansas and Texas)
• Primarily made of aeolian and fluvial sediments, which have high porosity and permeability
• Part of the High Plains Aquifer System, providing 30% of the groundwater used for irrigation in the US
• Water levels have dropped by up to 150ft in places due to a growing population and advances in automatic irrigation systems (e.g. the centre pivot irrigation method)
• The rate of recharge can be months or hundreds of years

Question 13

How is anthropogenic climate change affecting the water cycle?

Answer 13

• Increasing risk of intense rainstorm events and extreme droughts
• Evapotranspiration rates will increase may lead to drier soils
• Warmer air is able to hold more moisture so may lead to more intense storm events
• Water will run off overland which increases the likelihood of flash floods
• Predicting changes to individual drainage basins is very difficult though