🔵Water Cycle Flashcards
What drives change in a water cycle
Inputs,outputs, flows and stores.
- changes in these have impacts of varying magnitudes over different lengths of time
Water cycle inputs
Precipitation
What are the 3 main types if rainfall
Conventional - due to heating by the sun, warm air rises and condenses at higher altitudes then falls again.
Relief - warm air forced upwards by a barrier such as mountains, causing it to condense at higher altitudes and fall as rain.
Frontal - warm air rises over cool air when 2 bodies of air at different temperatures meet, because the warm air is less dense and lighter. It condenses at higher altitudes and falls as rain.
Water cycle outputs
Evapotranspiration - when water is heated by the sun (off plants) and becomes a gas.
Transpiration - occurs in plants when they respire (release h2O vapour through their leaves)
Streamflow - all water that enters a drainage basin will either leave through the atmosphere or through streams which drain the basin. These may flow as tributaries into other rivers or directly into lakes and oceans.
Water cycle flows - infiltration
Process of water moving from above ground into the soil.
Infiltration capacity - how quickly infiltration occurs.
Grass cops and tree roots create passage for water to flow through through from the surface into the soil, so increases the infiltration capacity.
Moderate / Fast
Water cycle flows - percolation
Water moves from the ground into porous rock or rock fractures. The percolation rate is dependant on the fractures that may be present in the rock and permability of the rock.
Slow
Water cycle flows - throughflow
Water moves through the soil and into streams or rivers. Speed of flow is dependant on the soil type.
Clay soils - high field capacity and smaller pore spaces have a slower rate.
Sandy soils - Darin quickly as lower field capacity and larger pore spaces and natural channels from animals such as worms.
Moderate / Fast
Water cycle flows - surface run off (overland flow)
Water flows above the ground as
- Sheet-Flow (lots of water flowing over a large area)
- Rills (small channels similar to steams, that are unlikely to carry water during periods where there is no rainfall)
Fast
Water cycle flows - Groundwater flow
Water moves through rocks - ensures theres water in rivers even in long periods of dry weather.
Jointed rocks (limestone) in karst environments where there are many underground streams and caves may transfer water very rapidly.
Usually slow but variable.
Water cycle flows - streamflow
Water the moves through established channels.
Fast
Water cycle flows - stem flow
Flows of water thats been intercepted by plants or trees, down a stem / leaf / branch or other part of a plant.
Fast
Water cycle stores and time lengths
Soil water - mid term (used by plants)
Groundwater - long term (porous rocks)
River channel - short term (water stored in river)
Interception - short term (water intercepted by plants)
Surface strange - variable (puddles, ponds, lakes)
Define the water table
Upper level at which the pore spaces and fractures in the ground become saturated.
Used by researchers to assess drought conditions, health of wetland systems and success of forest restoration.
Changes to water cycle LOCAL - deforestation
Less interception by trees so more surface run off.
Soil no longer held together by roots, soil water storage decreases.
Fewer plants to decrease in transpiration.
Changes to water cycle LOCAL - storm events
Large amounts of quick and high rainfall quickly saturate the ground to its field capacity. No more water can infiltrate for surface run off increases.
Strom events are less effective at recharging water stores than prolonged rainfall as over longer periods of time more water can percolate into ground water stores and there would be less overland flow.
Changes to water cycle LOCAL - seasonal changes
Spring - more vegetation growth so more interception
Summer - less rainfall, ground may be harder and more impermeable so increases surface flow.
Autumn - less vegetation so less interception and more rainfall (seasonal)
Winter - frozen ground may be imperials and encourage more runoff. Snow discourages runoff and takes time to melt, slowing down the process that occur in the water cycle.
Changes to water cycle LOCAL - agriculture
Pastoral farming - livestock trample the ground reducing infiltration.
Arable farming - ploughing increases infiltration by creating looser soil, Whcih decreases surface run off. However diffing drainage ditches increase run off and surface flow.
Hillside terracing - increases surface water storage and decreases surface run off.
Irrigation - can lead to ground water depletion
Changes to water cycle LOCAL - urbanisation
Creating roads and buildings which have impermeable surfaces are likely to have drains creates impermeable surfaces that reduce infiltration but increase the surface run off, reducing lag-time and increasing the flood risk.
Green roofs / SUDS - use grass to reduce the amount of impermeable surfaces helps tackle urban flooding
Define SUDS
Sustainable urban drainage systems
Soil water budget
Shows the annual balance between inputs and outputs in the water cycle and their impacts on the soil water storage availability.
Dependant on the depths the and permeability of the soil and bedrock. The maximum level of storage is called the field capacity.
Seasonal changes to the water cycles soil water budget
- autumn
Precipitation > evapotranspiration
Deciduous trees lose their leaves and the cooler temperatures mean that the plants photosynthesis less.
Soil moisture levels increase and a water surplus occurs.
Seasonal changes to the water cycles soil water budget
- winter
Potential evapotranspiration from plants reach a minimum due to the colder Tempe rates and precipitation continues to refill the soil and water stores.
Infiltration and percolation refill the water table.
Seasonal changes to the water cycles soil water budget
- spring
Feb-March = plants start to grow again and potential evapotranspiration increases as temperatures rise and plants photosynthesise more.
Water surplus still here.
Seasonal changes to the water cycles soil water budget
- summer
Hotter weather leads to utilisation of soil water as evapotranspiration rates peak and rainfall is minimal.
Evapotranspiration > precipitation
Soil water depletes and a water deficit may occur if there is long hot summer / spring or a lack of winter rainfall the year before.
Natural changes to the water cycle over time (and effects) - seasonal changes
Less precipitation, more evapotranspiration in summer because of higher temperatures.
Reduced flows in the water cycle in winter as water is stored as ice.
Reduced interception in winter, when deciduous trees lose their leaves.
Increased evapotranspiration in summer; deciduous trees have their leaves/higher temperatures.
Natural changes to the water cycle over time (and effects) - storm events
Causes sudden increases in rainfall, leading to flooding and replenishment of some water stores.
Unlikely to cause long term changes.
Natural changes to the water cycle over time (and effects) - droughts
Cause major stores to be depleted and the activity of flows acting within the water cycle to decrease.
May cause long-term change as they become more common as a result of climate change.
Natural changes to the water cycle over time (and effects) - El Niño and La Niña
The El Niño effect occurs every 2-7 years and causes warm temperatures in a predictable way.
The La Niña effect occurs every 2-7 years and causes cooler temperatures in a predictable way.
It is likely that climate change will increase the probability of more El Nino’s in future.
Natural changes to the water cycle over time (and effects) - cryospheric changes
In the past glaciers and icecaps have stored significant proportions of freshwater through the process of accumulation.
Currently, almost all of the world’s glaciers are shrinking, causing sea levels to rise.
If all the world’s glaciers and icecaps were to melt, sea levels would rise by around 60 metres.
Human changes to the water cycle over time (and effects) - farming practices
Ploughing breaks up the surface, increasing infiltration.
Arable farming (crops) can increase interception and evapotranspiration.
Pastoral (animal) farming compacts soil, reducing infiltration and increasing runoff.
Irrigation removes water from local rivers, decreasing their flow.
Human changes to the water cycle over time (and effects) - land use change
Deforestation (e.g. for farming) reduces interception, evapotranspiration and but infiltration increases (dead plant material in forests usually prevents infiltration).
Construction reduces infiltration and evapotranspiration, but increases runoff.
Human changes to the water cycle over time (and effects) - water abstraction
This reduces the volume of water in surface stores (e.g. lakes).
Water abstraction increases in dry seasons (e.g. water is needed for irrigation).
Human abstraction from aquifers as an output to meet water demands is often greater than inputs to the aquifer, leading to a decline in global long-term water stores.
