Water Insecurity - EQ1 Flashcards
What percentage of the earth’s water is freshwater?
2.5%
A closed system
Occurs when there is transfer of energy but not matter between the system and its surroundings (the inputs come from within the system)
An open system
Receives inputs from and transfers outputs of energy and matter to other systems
The water stores
Oceans, ice caps and glaciers (cryosphere), groundwater, rivers and lakes (surface water), soil moisture, atmospheric moisture, biological water (biosphere)
The global water budget
The annual balance of water fluxes (flows) and the size of the water stores
Fossil water
Water that has been contained in an undisturbed space, usually groundwater in an aquifer, for millennia or longer.
Inputs into the drainage basin
Precipitation
Stores in the drainage basin
Interception storage, surface storage, soil moisture storage, groundwater storage, channel storage
Flows (processes) in the drainage basin
Through fall, stem flow, surface runoff (overland flow), infiltration, throughflow, percolation, groundwater flow,
Outputs in the drainage basin
Evapotranspiration, channel flow
How does vegetation cover affect the rate of infiltration?
Roots help to break up the soil, increasing the infiltration rate
How does precipitation intensity affect the rate of infiltration?
Infiltration-excess overland flow will occur when rainfall intensity exceeds infiltration capacity, meaning that the water flows over the surface and infiltration is reduced
How does soil and rock type affect the rate of infiltration?
Infiltration rates will decrease as porosity and permeability increase
How does water table depth affect the rate of infiltration
As the water table rises during prolonged rainfall the soil will become saturated, reducing infiltration
How does slope gradient affect infiltration rates
As gradient increases more water will flow over the surface, reducing infiltration
How does temperature affect the rate of evapotranspiration
The rate of eases with temperature. The main energy source is solar radiation, so evaporation and temperature will increase with sunshine hours
How does wind affect the rate of evapotranspiration
Wind will increase the rate of evaporation by reducing the relative humidity and preventing saturation of the air
How does vegetation cover affect the rate of evapotranspiration
Transpiration will increase with increased vegetation cover, which will depend on the type of vegetation and the season. Vegetation with a low albedo (reflectivity) such as dark forests will increase more solar radiation, increasing evaporation
How does soil moisture content affect the rate of evapotranspiration
Will determine the amount of water available for transpiration. It is dependent on soil and rock permeability
Human disruptions to the drainage basin hydrological cycle: cloud seeding
The attempt to change the amount or type of precipitation by dispersing substances into the air
Human disruptions to the drainage basin hydrological cycle: urbanisation
Urbanisation creates impermeable surfaces that reduce infiltration and increase surface runoff and throughflow through artificial drains; stream and river discharges often increase rapidly as a result
Human disruptions to the drainage basin hydrological cycle: dam construction
Damns increase surface water stores and evaporation and reduce downstream river discharge
Human disruptions to the drainage basin hydrological cycle: groundwater abstraction
In some locations, groundwater is abstracted from aquifers faster than it is replaced, causing reduced groundwater flow and a lower water table. In other locations, reduced industrial activity or deforestation has increased groundwater storage, increasing the risk of groundwater flooding if the water table reaches the land surface
Precipitation (P)
= channel discharge (Q) + evapotranspiration (E) + change in storage (S)
Soil moisture surplus
Precipitation is greater than potential evapotranspiration and the soil water store is full, so there is a surplus of soil moisture for plant use, runoff into streams and recharging groundwater supplies. The soil is said to be at field capacity.
Soil moisture utilisation
Potential evapotranspiration increases and exceeds precipitation, so there is more water evaporating from the ground surface and being transpired by plants than is falling as rain. Water is also drawn up from the soil by capillary action. The water is gradually used up.
Maximum annual temperatures
High temperatures cause maximum evapotranspiration, precipitation is at a minimum and therefore plants use up the soil moisture store. River levels will fall and crops will need irrigation.
Soil moisture deficiency
The soil water store has been used up by high rate of evapotranspiration and low precipitation. Plants can only survive if they are adapted to periods of drought or are irrigated
River regime
Described the annual variation in the discharge of a river
Storm hydrograph
Shows variations in a river’s discharge at a specific point over a short period of time
Norma (base) flow
The contribution to river flow from long-term storage sources such as permeable rocks, areas or bog and marsh and peat covered moorlands
Rising limb
The increase in discharge in response to surface runoff and throughflow from a rainfall event, unit, peak flow is reached. When the storm begins, the river’s initial response is negligible as the precipitation takes time to reach the channel.
Falling limb
The decline in discharge that occurs after peak flow, this segment is usually less steep than the rising limb because throughflow is being released relatively slow into the channel.
Lag time
The difference in hours and minutes between the time of maximum precipitation and the time of peak discharge. The lag time varies according to drainage basin conditions. Rivers with a short lag time tend to experience a higher peak discharge and they are more prone to flooding than rivers with a long lag time.
Storm runoff
The part of the river flow derived from the immediate rainfall event. The most rapid transfer of water occurs overland and via throughflow.
Approach segment
Shows the discharge of the river before the storm (the antecedent flow rate)
