Water Questions Flashcards
Explain how water is stored and flows within the hydrological cycle?
The largest store of water is our oceans. As the ocean is heated by solar energy from the sun, water molecules off the surface of the ocean evaporate, 41310(3)km(3)/year, rising into the atmosphere which is the largest transfer in the cycle. Once in the clouds, the cooler temperatures of this location means that water transforms from water vapour to form water droplets - condensation. When the water is too heavy to be stored in the atmosphere, it will eventually fall as precipitation. The precipitation falls to the surface. This can then return to rivers, lakes or oceans directly. This precipitation may also be intercepted by vegetation, which returns this to the atmosphere via evapotranspiration (7310(3)km(3)/year. Alternatively, the water can infiltrate or percolate into soil or rock and become part of throughflow or groundwater flow where it will eventually end up being stored in the ocean. Water can also precipitate onto mountains and becomes part of the cryosphere where it is locked up in snow on the tops of mountains in the cold; this can melt and become surface run-off down mountains and eventually end up in the ocean, lakes or rivers again.
Explain the global water budget and factors that affect it?
Water budgets show the annual balance between inputs (precipitation) and outputs (Evapotranspiration and channel flow). Regions can either have a negative balance or a positive balance, on a local scale water budgets show how annual variation between precipitation and evaporation can impact the amount of –
Explain how physical factors affect the drainage basin system?
A drainage basin is an area of land that is drained by a river and its tributaries, it is an open system within the global hydrological cycle. The geology of a drainage basin can affect the rate of percolation and groundwater flow. Porous rock will allow infiltration to occur as water will fill pores within the rock, creating groundwater storage or aquifers. This can decrease surface run off into streams and rivers and increase ground water flow and through flow which will eventually lead to rivers and oceans.
The relief of a drainage basin will also effect this system. The steeper relief the more surface run off will occur down the slope, ending up in lakes and rivers. Alternatively, the flatter the relief the more infiltration will take place as water will have time to do so, becoming part of throughflow or groundwater flow.
Vegetation largely affects the drainage basin. Large amounts of vegetation cover will lead to more interception, especially in coniferous vegetation that intercepts 25-30% of precipitation. This can lead to stemflow into the soil This can also slow down overland flow or surface run off in addition to evapotranspiration.
The soil of a drainage basin can also affect it. The amount of pores in the soil will allow infiltration of water. Meanwhile, compacted soil surfaces will inhibit infiltration as will atecedent soil moisture - if the soil is already saturated with soil. In addition to this, the type of soil is also intertwined with vegetation cover. Healthy, fertile soil will lead to more vegetation cover and therefore more interception and evapotranspiration.
Explain how humans can interfere in the water cycle?
Also fits into how humans can interfere with the drainage basin system?
Urbanisation creates impermeable surfaces that reduce infiltration and increase surface run off as well as throughflow with artificial drains. This leads to stream and river discharges rapidly increasing –> causing the UK to now have a flow risk.
Groundwater abstraction can mean that sometimes groundwater is extracted faster than the aquifers can be replenished causing reduced ground water flow and lowering the water table. In other locations, reduced industrial activity has increased groundwater storage, increasing risk of flooding if the water table reaches the land surface.
Dams can increase surface water stores and evaporation, as well as reducing downstream river discharge. For example, Lake Nasser behind the Aswan Dam in Egypt is estimated to have evaporation losses of 10 to 16 billion cubic metres every year.
Deforestation can also affect water availability/ the drainage basin. Over 20% of the Amazon Rain forest has been destroyed for commercial and agricultural purposes. Up to 75% of water is returned to the atmosphere via evapotranspiration in the Amazon, which reduces to 25% when the forest is cleared. As more water runs off into the Amazon drainage system, there is the risk of severe flooding and also aquifer depletion as less water infiltrates to recharge them. Overland flow also increases the amount of soil erosion as nutrients are washed away.
Explain the physical factors affecting river regimes
A river regime describes the annual variation in the discharge of a river at a particular point of gauging station.
The geology and overlying soils will affect river regimes. Impermeable rock such as igneous will lead to higher peak discharges (flashy) due to increased surface run off whereas permeable rock and soil surfaces will allow the water to gradually reach the river with a long lag time (subdued) through throughflow and ground water flow after it has percolated.
The size of the drainage basin will also impact this as larger drainage basin like the Amazon River will experience more subdued river regimes compared to smaller drainage basins which will see flashier river regimes due to the shorter lag time for precipitation to reach the river.
In addition to this, the temperatures experienced in the basin will also affect in. A tropical climate will experience more precipitation and therefore a higher peak discharge, like the Nile River which has a tropical humid climate near its source in lake Victoria. Alternatively, wet and dry seasons may cause snow melt which will lead to a peak discharge in summer months. Such is the case in the Amazon River due to snow melt from the Andes.
Another factor affecting river regimes is where the gauging station is / where the measurements are taken from. This is because many large rivers have varied catchments. For example, the Nile River experiences both a tropical humid climate near its source in Lake Victoria and an Arid hot climate in Sudan and Egypt. A tropical climate would see more river discharge due to increased precipitation meanwhile a more arid climate, like the Nile in Sudan and Egypt, would experience less due to evaporation from solar energy and limited precipitation.
Explain how physical factors affect the shape of storm hydrographs?
TALK ABOUT HIGH PEAK DISCHARGE, AND GENTLE RISING LIMB
Storm hydrographs show the variation of discharge within a short period of time, normally an individual storm or group of storms not more than a few days in length; it records the changing discharge of a river or stream in response to a specific input of precipitation.
Precipitation: If there is prolonged rainfall soil becomes saturated so less infiltration occurs and more surface run-off, leads to more flashy storm hydrograph with shorter lag time. Intense stores mean that rainfall exceeds infiltration capacity. Heavy rain compacts the soil and increases surface run off leading to a shorter lag time, flashy storm hydrograph. Also, snowmelt can lead to flashy storm hydrograph as it occurs rapidly therefore increasing the volume of water in the system and decreasing the lag time - the cold temps mean the soil is frozen so increased surface run off. Alternatively, if rain falls gently over a long period of time it encourages infiltration and increases ground water storage.
High vegetation coverage will lead to a subdued/ steady storm hydrograph. This is because vegetation will increase interception of rainfall, allowing evapotranspiration to take place and reducing surface run-off. Stemflow can also allow water to travel as throughflow or groundwater flow very steadily over time into a river. A lack of vegetation will increase surface run off and create a shorter lag time and a flashy storm hydrograph.
Land use can also affect storm hydrographs. Urban surfaces are harder, with roads and concrete structure increasing surface run off to the rivers. In addition to this, the use of drains will carry water rapidly and directly to a river, shortening lag time and producing a flashy storm hydrograph. Rural areas will experience more steady storm hydrographs. This is because vegetated surfaces intercept water and allow infiltration so water travels slowly to the river channel, with a gentle rising limb and thus a longer lag time.
Small drainage basins will produce a flashy storm hydrograph as precipitation from a storm event will reach a channel rapidly due to the shorter distance to travel. Alternatively, large basins will experience subdued hydrographs will lower peak discharges and longer lag times as it takes the precipitation longer to reach the channel.
Explain the physical causes of drought?
Drought is a water deficit in a location over time, this can be either meterological, agricultural or hydrological. One physical cause of this are ENSO cycles. La Nina involves the intensification of normal conditions with a strong Walker cell; an increase in the undercurrent and very strong upwelling of cold water off the coast of western South America, creating an area of high pressure and drought conditions. El Nino involves the reversal of pressure systems and weather patterns, occurring every 3-7 years; trade winds blow warm waters westwards through the reversal of trade winds. The reversed Walker cell creates a cooler area of high air pressure over Australia, creating drought conditions.
In addition to ENSO cycles, blocking anti cyclones can also create drought conditions. Anticyclones are areas of high pressure where air is sinking, associated with dry conditions. Blocking anticyclones at the ITCZ prevent the migration of the ICTZ north, creating drought conditions. At the jet stream locking anticyclones prevent the migration of the stream south towards the UK, preventing condensation and frontal rainfall, creating drought conditions
Explain how human activity increases the risk of drought?
Deforestation reduces the ability of the soil to store water through increased soil erosion, reducing soil water availability. This can also reduce evapotranspiration from trees and in turn, precipitation. For Example, Up to 75% of water is returned to the atmosphere via evapotranspiration in the Amazon, which reduces to 25% when the forest is cleared.
Over-grazing: the grazing of farmland that exceedds the carrying capcity prevents the soil from recovering, reducing the soil profile and soil water availability. The Sahel region of Africa has been suffering from drought on a regular basis since the early 1980s. Human activities such as overgrazing worsen extreme wet and dry seasons in the Sahel causing severe drought.
Over-abstraction of surface water reduces the amount of water stored in surface stores, including lakes and river, reducing fluxes like river discharge, throughflow and surface run off. For example, 14% of rivers are over-abstracted in England. In addition to this, the over-abstraction of groundwater stores reduces the groundwater flow as the water table falls and aquifers cant be replenished. For example, following the 1960s green revolution in India where electric pump technology became available groundwater levels have fallen by 5m since 1980 in half of India’s districts.
Changes to albedo, the amount of solar energy reflected from the Earth’s surface back into space, can also increase drought risk. Areas with no snow/ice cover (such as soil which only reflects 35% of UV) will absorb more heat. This in turn will cause ocean, lake and river stores to experience more evaporation.
Explain the physical causes of water insecurity?
Water insecurity can be caused by low precipitation inputs. For example, continentality. The distance from the coast affects the amount of precipitation as air masses traveling over land lose moisture due to orographic and cyclonic rainfall. Interiors of large continents therefore receive very little precipitation.
Orographic rainfall in mountainous regions can also lead to water insecurity. When air is forced to rise over a barrier like a mountain, it cools and condensation takes place forming rain. The downward slopes receives little rain, areas in the rain shadow will have less access to water.
One physical cause of this are ENSO cycles. La Nina involves the intensification of normal conditions with a strong Walker cell; an increase in the undercurrent and very strong upwelling of cold water off the coast of western South America, creating an area of high pressure and drought conditions. El Nino involves the reversal of pressure systems and weather patterns, occurring every 3-7 years; trade winds blow warm waters westwards through the reversal of trade winds. The reversed Walker cell creates a cooler area of high air pressure over Australia, creating drought conditions.
In addition to ENSO cycles, blocking anti cyclones can also create drought conditions.
What is water stress?
When renewable water resources are between 1,000m3 and 1,700m3 per capita per year. Water stress is concerned with availability not access, Therefore it is possible for a nation to have low water stress but be economically water insecure (many partys of equatorial Africa have high availability but limited access)
What is water stress?
When renewable water resources are between 1,000m3 and 1,700m3 per capita per year. Water stress is concerned with availability not access, Therefore it is possible for a nation to have low water stress but be economically water insecure (many parts of equatorial Africa have high availability but limited access)
Explain the human causes of water insecurity?
Over-abstraction can lead to water insecurity. Over-abstraction from groundwater stores (human) means that there is less groundwater flow and the water table is lower meaning that aquifers may not be adequately recharged during precipitation events – especially if unrenewable ‘fossil water’ stores are abstracted from. In regions like the Sahara Desert fossil water is a none renewable source.
Pollution and contamination (human) involve water sources, including rivers and lakes, becoming unusable from industry for consumption as such is dangerous to consume. It’s estimated that around 70% of surface water in India is unfit for consumption
Saltwater incursion can also increase water insecurity. The Citarum river in Indonesia is the worlds most polluted river with no less than 20,000 tons of waste deposited every day. Many of the small, low lying Pacific Islands depend on small aquifers for their freshwater supply; for example, 35% of Samoa’s water supply is drawn from aquifers. These aquifers are threatened by saltwater intrusion as a result of over-abstraction, climate variability and sea-level rise. Crop production depends on freshwater irrigation, making saltwater intrusion a serious threat to health, food security and livelihoods.
What are the physical causes of flooding?
Monsoon rainfall is a physical cause of drought. In June the ITCZ moves towards the tropic of Cancer and the intense heating of the ITCZ creates low pressure in Northern India. Meanwhile, as the Indian Ocean heats up an anticyclone is created off India. This leads to heightened rainfall and flooding throughout Northern India.
There is also tidal flooding, often a result of storm surges or when high river flows meet particularly high spring tides in estuaries. A storm surge is caused by very low air pressure which raises the height of the high-tide sea. Strong onshore winds then drive the ‘raised’ sea towards the coast, often breaching coastal defences and flooding large areas.
Flooding can also be caused by glacial outburts. This is what occurs as ice dams melt draining glacial lakes. Similarly, rapid snow melt in Spring and summers will result in an increase in water. Such as in the Andes into the Amazon river.
El Nino involves the reversal of pressure systems and weather patterns, occurring every 3-7 years; trade winds blow warm water westwards through the reversal of trade winds. Convectional uplift occurs as water flows east with warm, moist air rising over western South America, creating an area of low pressure and heavy rains
Explain how human activity increases the risk of flooding?
Deforestation reduces the ability of soil to store water meaning reduced interception (especially in coniferous trees that intercept 25-30% of precipitation) and surface run-off. This will increase river discharge and increase the risk of fluvial flooding. The UK 2015 floods were worsened by the fact that there was only 10% vegetation cover.
River straightening and dredging can also increase river discharge and speed of flow, increasing the risk of fluvial flooding. This means that impeding bridges through a channel will slow down river discharge and result in the spillage of water over flood banks.
Urban surfaces are harder, with roads and concrete structure increasing surface run off to the rivers. In addition to this, the use of drains will carry water rapidly and directly to a river, shortening lag time and increasing fluvial flooding.
Nearly 70% of Pakistan’s population work in the agricultural sector, and live close to rivers that are used to irrigate crops. Rural communities are vulnerable to flooding because compacted soil surfaces will experienced heightened surface run off and flooding of rivers.
Explain the factors causing a rise in water demand?
There are increasing populations around the world, with an 80 million population increase per year, especially in less-economically developed counties means that there is increasing demand for water among a growing population for personal consumption.
Growing populations and changing demand for more water-intensive foods (60% increase in global agricultural to meet food demand by 2050), such as beef in China (Changing diets), means that there is more demand for water use in agriculture to satisfy this growing demand.
Living Standards
Industrialisation, especially in LEDCs and newly industrialised countries, means that there is increasing demand for water use in industry, including the production of consumer goods and energy plants. For example, there will be a 400% increase in global water demand for manufacturing by 2050.
Rising standard of living, especially in NICs, means that there is increasing demand for more water-intensive diets and for households goods as income rise such as washing machines and wider access to showers.
