The Water cycle - Local scale Flashcards
Where would you find a local scale water cycle?
A local drainage basin system
Is a local-scale water cycle an open or closed system?
Open
What are the inputs to a local-scale water cycle?
Precipitation - Rain, snow, hail
What are the three types of rainfall?
Convectional, Relief, Frontal
What is convectional rainfall?
Due to heating by the sun, warm air rises, condenses at higher altitudes and falls as rain
What is relief rainfall?
Warm air forced upward by a barrier such as mountains. Causes it to condense at higher altitudes and fall as rain
What is frontal rainfall?
Warm air rises over cool air (less dense). Condenses at higher altitudes and falls as rain
What are the outputs of a local-scale water cycle?
Evapotranspiration (evaporation & Transpiration).
Streamflow
What is evaporation?
Occurs when water is heated by the sun, causing it to become a gas and rise
What is transpiration?
Occurs in plants when they respire through their leaves, releasing water they absorb through their roots (then evaporation from sun)
What is streamflow?
All water that enters the atmosphere leaves by either entering the atmosphere..
Or through streams which drain the basin. They may flow as tributaries into rives or directly into lakes and oceans
What are the flows of a local-scale water cycle? (7)
Infiltration, percolation, throughflow, surface runoff (overland flow), groundwater flow, streamflow, stemflow
What is infiltration?
Water moving from ground into soil.
What is an infiltration capacity?
Refers to how infiltration occurs.
Grass crops and tree roots create passages for water to flow (increase infiltration).
If precipitation falls at greater rate than infiltration capacity, overland flow will occur
What is percolation?
Water moves from ground into porous rocks or rock fractures
What is a percolation rate?
Dependent on the rock fractures and the permeability. (Slow)
What is throughflow?
Water moves through soil into streams or rivers
What controls the rate of throughflow?
Dependent on the type of soil.
Clay soils with high field capacity and smaller pore spaces have slower rates.
Sandy soils drain quickly because they have lower field capacity and larger pore spaces and natural channels from worms. (moderate/fast)
What is surface runoff (overland flow)?
Water flows above the ground as sheetflow (lots of water over larger area) or rills (small channels/streams)
What is groundwater flow?
Water moves through rocks.
(usually slow but is variable)
What is streamflow?
Water moves through established channels (fast)
What is stemflow?
Flow of vegetation intercepted water (fast)
What are the long-term and short-term stores of a local-scale water cycle?
Short-term:
River channel, interception
Mid-term:
Soil water
Long-term:
Groundwater
Variable:
Surface storage
What is a soil water store?
Water stored in soil - utilised (used) by plants.
What is a groundwater store?
Water stores in pore spaces in rock
What is a river channel store?
Water stored in a river
What is an interception store?
Intercepted water remains on plants until it reaches the ground
What is a surface storage store?
Water in puddles, ponds, lakes, etc
What is the water table?
The upper layer at which pore spaces and fractures in the ground become saturated.
What is the water balance?
The process of water storage and transfer in a drainage basin
What is the formula for water balance?
Precipitation = Total runoff + evapotranspiration +/- (change in) storage
What controls the water balance of an area?
Physical factors, especially during seasonal variations of temperature and precipitation.
What causes changes in a local water cycle? (5)
Deforestation, Storm events, seasonal changes, agriculture, urbanisation
How does deforestation impact the local water cycle?
Less interception by trees - Surface runoff increases
Soil no longer held together by roots - soil storage decreases.
Transpiration decreases
How do storm events impact local water cycles?
Large rainfall - Saturates ground quickly to its field capacity
No more water can infiltrate - increase runoff - less replenishment of groundwater stores (aquifers)
How do seasonal changes impact local water cycles?
Spring: More vegetation growth - more interception
Summer: Less rain (usually). Ground may become harder/more impermeable - encouraged runoff
Autumn: Less vegetation growth - less interception. more rainfall
Winter: Frozen ground may be impermeable - encouraged runoff. Snow discourages runoff - slows down water cycle processes
How does agriculture impact the local water cycle?
Pastoral farming: trample ground - reduce infiltration
Arable farming: Ploughing increases infiltration - decreases runoff. Digging drainage ditches increase runoff and streamflow
Hillside terracing: (rice padi) increase surface water storage - decrease runoff
Irrigation: Groundwater depletion
How does urbanisation impact a local water cycle?
Roads and buildings created - impermeable - reduced infiltration - increase surface runoff - reduced lag time - increasing flood risk.
Green roofs and SUDS.
What is SUDS?
Sustainable Urban Drainage Systems. Reduce the amount of impermeable surfaces - reduce flooding
What is the soil water budget?
Shows the annual balance between inputs and outputs in water cycles, and their impact on soil water storage/availability
Why are soil water budgets never the same?
Varying conditions each year. How much rainfall or how dry it was. Also type, depth and permeability of soil and bedrock.
What is the field capacity?
The maximum possible level of storage of water in soil
How does Autumn impact the soil water budget?
Greater inputs (precipitation) than outputs (evapotranspiration) as trees lose leaves and temps cool (less photosynthesis).
Soil moisture levels increase and a water surplus occurs
How does winter impact the soil water budget?
Potential evapotranspiration from plants reaches minimum (colder temps). Precipitation refill soil water stores.
Infiltration and percolation refill water table
How does spring impact the soil water budget?
Plant growth. Potential evapotranspiration increases. Temps increase = more photosynthesis
Still a water surplus
How does summer impact the soil water budget?
Utilisation of soil water as evapotranspiration peaks and rainfall at minimum.
Evapotranspiration outputs greater than inputs - soil water stores depleting.
Water deficit may occur.
What is a water surplus?
When there is more water than what is needed
