Water Cycle 2 Flashcards
Give 4 possible ways human can affect the water cycle within a drainage basin (local scale)
Throughout the world there have been major changes to the water cycle from climate change and land use change
Deforestation means there is less interception so overland flow increases. Also decreases evapotranspiration so maybe less precipitation from conventional rainfall
Land use change may increase flood risk (urbanisation, deforestation)
Humans modifying the flows of rivers by abstraction of water (dams). When water is released back it may be of different tempatue/quality
Give 3 types of system
Open
Closed
Isolated
What is an open system
Moist environment systems are open and there are inputs and outputs of both energy + matter
What is a closed system
Inputs and output of energy but not matter (planet earth)
What is an isolated system
No input or output of energy or matter (universe)
Some claim this idea is not applicable to geography
What is dynamic equilibrium
When opposing inputs and outputs in the system are balanced
Give an example of a cause on the water cycle for disrupting the dynamic equilibrium of a system
Prolonged heavy rainfall causes an increase in the discharge and velocity of a river, increasing rate of erosion
How do Chroley and Hagget describe systems
A simplified structuring fo reality which presents significant features/relationships in a. generalised form, allowing the fundamental aspects of reality to appear
An open system tends to…….itself by modifying the interrelationships between different elements fo the system so….and output flows………each other out
Adjust
Inputs
Balance
What is feedback
Occurs when one element of a system changes because of an outside influence, upsetting the dynamic equilibrium
What is negative feedback
When a system acts by lessening the effects of the original change and ultimately reverses it
What is positive feedback
When a change causes a further/snowball effe t, continuing or accelerating the original change
What is the dew point temperature
The temperature bellow which droplets begin to condense and dew forms (air saturated)
How does precipitation vary worldwide
Influenced by general circulation of the atmosphere, proximity to large bodies of water and topography
Give the 4 global stores of water, their percentage of total water and residence time
Hydrosphere (97%) 3,600 years
Lithosphere (1.7%) 10,000 years
Cryosphere (1.7%) 15,000 years
Atmosphere (0.001%) 10 days
Why are residence times longer in larger stores
Big stores - vast majority fo water molecules are very far from he boundary and thus takes a long time to escape
Are the cryosphere and hydrosphere in a state of equilibrium
No
Crysophere - more out than in
Hydrosphere - More in than out (Global warming) (opposite in ice age - temperature dependent)
Lithosphere and atmosphere tend not to change a great deal
What does the atmosphere have such short residence times
Water only stays in atmosphere if not very dense (air can only hold so mcc water for a limited amount of time)
Do the water stores experience a significant change in volume
Whilst the overall volume of water contained in stores does not change significantly on the global scale, transfers and flows will affect the amount of water over time that remains in a store
An example = how levels of evaporation increase in summer which leads to higher atmospheric storage and a slight drop in ocean storage.
However, these are not significant changes in volume and the ocean will always remain the primary store in water cycle
Give 4 transfers that slightly change the size of the stores
Evaporation
Condensation
Cloud formation
Precipitation
How does evaporation affect the amount of water held in stores
The level of evaporation on global scale ocean and sea levels is minima but within a drainage basin, evaporation can have a large regional impact
Lakes/rivers in areas of high summer temperatures will experience high levels of evaporation and hydrological storage will reduce significantly in that area
How do clouds form
When water molecules aggregate - temperatures drop at altitude to allow condensation
How does precipitation occur
When the water molecules within a cloud combine and become to big (coalescence)
If the droplets fall velocity is greater than the clouds updraft velocity, precipitation will occur
Give 4 reasons for differing rainfall patterns globally
Desert areas have limited rainfall as they receive sinking dry air from pressure systems
Large continental interiors tend to be dry because of distance from moisture sources and many clouds loose moisture before they reach the centre of large continents
Polar areas are dry because cold air cannot hold as much moisture as warm air, less precipitation
Areas near equator receive high rainfall amounts because constant solar heating produces intense heating, large-scale evaporation and moist rising air that cools with altitude and forms convectional rainfall
Why do mountain ranges near water sources reviewed high levels of precipitation
Precipitation occurs when clouds rise to go over mountains and the air cools which encourages the water molecules to join and then precipitation occurs (relief rainfall)
Why are hydrographs important
Can be used in predicting the flood risk and in making the necessary changes
Put factors influencing hydrographs into 3 groups
Climate
Natural catchment
Land use
How do 3 different types of precipitation influence the shape of a hydrograph
Prolonged rainfall - flashy hydrographs most frequently occurs following a long period of heavy rainfall when the ground has become saturated
Intense storms - when heavy rain occurs, the rainfall intensity may be greater than the infiltration capacity of the soil, causing surface run-off and flash floods
Snowfall - heavy snowfall means water is held in storage and river levels drop initially. When temperatures warm, meltwater soon reaches river though ground may be frozen so infiltration impeded
How does temperature influence infiltration
Extremes can restrict infiltration and increase surface runoff
Very cold (frozen) in winter Hot, dry in summer
Gve some interrelationships between factors influencing the shape of the hydrograph
When considering natural catchment characteristics, geology is an important control
Fcsators that impact on the hydrograph like rock permeability, groundwater storage capacity and soil type all stem from the underlying geology
Combination of a multitude of factors that will determine the shape of the hydrograph
How big is the Mississippi drainage basin
4th largest in the world (1.2 million square miles)
Give 3 physical factors that influence the run-off and consequently, flow of the Mississippi-river
Precipitation/snowmelt
Corresponding variability between precipitation and evapotranspiration
Weather events - storms/droughts
How does precipitation/snowmelt affect the flow of the Mississippi River
Maintained by precipitation/snowmelt (paramount factor), however, not all runs off into river channels
Some infiltrates into spil and is eventually transpired or evaporated directly
Over the basin, evapotranspiration losses account for over 75% the annual precipitation
However, these losses vary regionally. Arid western part, very little water is left to run off and most of the river’s run off is indebted to wetter eastern part of basin
How does variability in precipitation and evapotranspiration affect the flow of the Mississippi River
Flow varies over time
Seasonally, there is an increase in precipitation in winter months compared to drier summer months. However, this simple seasonal pattern is far too simplistic and there is a variability in precipitation levels within the seasons
North west region receives lower rainfall than the S.E corner, particularly Nov-Feb. The uneven nature of rainfall distribution as well as the amount of it significantly alters runoff levels throughout the year
How do weather events (storms) affect the flow of the Mississippi River
Impact upon the amount of runoff within the basin and the flow shape of the hydrograph
High levels of precipitation can lead to saturated soil as soil water storage limits are reached
This can lead to increased surface runoff which increases discharge within river channel
E.g 2014 summer - record rainfall fell in Minnesota, Iowa and Illinois leading to a flood in the upper Mississippi basin
How do weather events (droughts) affect the flow of the Mississippi River
Limited precipitation reduce river discharge initially
However, over a longer time period, drought conditions can harden the soil, making it impermeable and increasing runoff during a period of subsequent rainfall
What is the main human activity that significantly influences runoff in the Mississippi River
Agriculture
Constitutes a key economic activity in arid western part which provides 92% USA’s total agricultural exports
How does agriculture influence the Mississippi River
Large volumes of runoff are collected in man-made reservoirs, which is then extracted and irrigates crops
Changes the water cycle as water is diverted from surface runoff/infiltration and through flow - greatly impacting the amount water reaching the river Chanel
Storage and mass use off irrigation results in higher levels of evapotranspiration from crops, so water returned to atmosphere instead of hydrosphere
Give 3 human impacts on the Mississippi River
Agriculture
Reservoirs
Climate change
How do reservoirs influence the Mississippi River
43 dams along course of Mississippi which hold back water
6% of total runoff is transferred to atmosphere by the higher levels of evaporation during summer from surface reservoirs
Increasing population and demands for domestic and uindustrial use has meant it will only continue
How does climate change influence the Mississippi River
Predictions estimate a reduction of 5 inches of rainfall a year in the lower basin due to changing precipitation patterns
Less rainfall = decreasing runoff and channel flow
What is meant by potential evapotranspiration
The highest amount of evapotranspiration possible (theoretical) with unlimited water
Define the water balance
Balance between the inputs and outputs of a drainage basin
