Summary
A Level Geography - Water Summary revision notes
- Module
- Water
- Institution
- PEARSON (PEARSON)
Summary revision notes for Geography - Water - Pearson Edexcel specification, with all case studies included
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The hydrological cycle is the circulation of water around the earth. It’s a closed systemso there are no external inputs and outputs, so nothing is lost or gained. It’s driven by solar
and gravitational potential energy.
- The hydrology in polar regions is different to tropical rainforests. EG: Different
temperatures affect evapotranspiration, amount and types of rainfall, and amount of
vegetation affects interception and infiltration.
Global Water Budget = This is all the water that is held in stores and flows of the global
hydrological cycle. It limits the water available for human use. Only 2.5% of the global water
is fresh, and the rest is ocean water (which is the biggest store of water globally). Only 1% of
the freshwater is easily accessible. Most of it is held in ice and glaciers.
More water is evaporated from the oceans than falls on to them as precipitation, and more
water falls as precipitation onto the land masses than is evaporated. If the precipitation and
evaporation budget did not work in this way, the land masses would dry up, and oceans
would flood. Therefore, the global water budget is essential for human use and survival.
- STORES : ⅔ of freshwater is locked in the cryosphere (Glaciers and ice sheets).
When climate warms, it melts. This is called cryosphere loss. It’s not renewable.
- STORES : Fossil Water is ancient deep groundwater made from wetter (Pluvial)
periods in the geological past. It exists in polar and desert regions like the Sahara.
New technologies made it possible to extract this water. However, it’s not renewable.
- Not being renewable has implications for future human access.
- Surface water is another store, which includes rivers, lakes, groundwater, and
moisture held in soils.
- Atmosphere is another store.
- Each store has its own residence time, which is the length of time the water would
remain stored. EG : High residence time in ocean and ice caps and fossil water, but
low in surface water.
Fluxes are the rates of flow between stores. The greatest fluxes occur over the oceans.
- The tropics receive intense solar radiation = high evaporation. Trade winds transfer
water to the ITCZ (a wide belt of clouds within the tropics) where convection currents
lift the air so it cools, condenses into clouds causing heavy rainfall - so the ITCZ is
the biggest flux transferring water from ocean to land
Thermohaline circulation = Ocean circulation. This is where ocean water in polar regions is
colder and saltier so denser than water in the tropics, so it sinks. This travels to warmer
areas and warmer areas travels to colder areas.
,The drainage basin is an area of land that is drained by a river and its tributaries with a
boundary known as the watershed. It’s an open system.
INPUT
1) Precipitation
- Convectional rainfall = Seawater evaporates due to solar radiation and high
temperatures. This leads to warm air to rise, which cools at saturation point
and condenses as condensation nuclei which gets heavier and big enough for
gravity to work and clouds form, which leads to rainfall. These mostly occur in
the equator.
- Frontal (Cyclonic) Rainfall = Formed in low pressure areas such as the UK.
This occurs when warm moist air from the South-West meets colder polar air
from the North-West. The warmer air is forced to rise over the denser colder
air. When this rises, the air cools and condenses as condensation nuclei and
cloud formation leading to rainfall.
- Relief (orographic) Rainfall = Warm moist air forced to rise over high areas
such as mountains or hills, which cools and condenses forming clouds. This
allows rainfall.
Factors which affect precipitation
- Type - snow - entry of water into drainage system delayed due to it needing to melt.
- Seasonality - Winter there’s more precipitation as opposed to summer.
- Amount of precipitation will affect drainage basin discharge.
- Intensity - more intense means more likely to flood due to it being hard to infiltrate.
Flux
1) Interception - Intervention of plants leaves whereby the water is stored in vegetation
which is eventually evaporated or absorbed by vegetation. This is greatest at the
start of a storm.
- A plant's interception varies with the type of vegetation. EG : Coniferous
forest trees have dense needles which allow greater accumulation of water.
- Meteorological conditions such as wind speeds can decrease interception
rates.
- Season - Winter there’s less leaves so less infiltration.
2) Infiltration - Process by which water soaks from surface into the soil. The infiltration
capacity depends on :
- Soil texture - sandy soil has more infiltration than clay
- Steep slopes would mean more surface runoff so less infiltration
- Previous precipitation - less capacity for soil to infiltrate precipitation.
- Type and amount of vegetation and seasonal changes - winter there’s less
leaves so less interception so more infiltration.
, FLOW
1) Surface runoff = water flowing overland. This occurs faster when the gradient of the
land is greater - steep. Also, if there’s vegetation or barriers, there’s less surface
runoff. If the ground is impermeable, there’s more surface runoff.
2) Throughflow = Movement of water downslope through the soil. It’s speed is
dependent on :
- Type of soil - Clay there’s slower flow rate unlike sand.
3) Percolation = Infiltration from soil to permeable rocks. This rate is dependent on the
permeability of the rock.
4) Groundwater flow = Flow transfer of percolated water through permeable or porous
rocks
OUTPUT
1) Evaporation = Process by which moisture is directly lost into the atmosphere from
water surfaces. The influencing factors are :
- Temperatures and hours of sunlight
- Size of water body is greater means there’s more evaporation.
- Vegetation cover or built-up environment stopping sunlight from reaching
water means less evaporation.
- Colour of surface beneath water. White can reflect sunlight but black absorbs.
2) Transpiration = Biological process by which water is lost through pores of plants
(stomata) into the atmosphere.
PHYSICAL FACTORS AFFECTING DRAINAGE BASIN
1) Climate = Influences the amount of precipitation and evaporation. It also has an
impact on the amount and type of vegetation. It’s the most influential factor due to it
being a global factor so difficult to control. It also affects all processes.
2) Soil composition = Influences amount of infiltration and throughflow. Eg : Sandy soils
there’s more infiltration and throughflow as opposed to clay.
3) Geology = Impacts Percolation and groundwater flow ( so impacts aquifers).
4) Relief = Steeper gradients means more surface runoff. Higher altitudes means more
precipitation totals.
5) Vegetation = Affects interception and infiltration, overland flow and surface runoff and
transpiration rates.
Climate is the most influential factor because it’s global but others are local factors so only
have an impact on certain areas.
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