Operation and Importance of Hydrological Cycle :thunder_cloud_and_rain:…
Operation and Importance of Hydrological Cycle :thunder_cloud_and_rain:
Hydrological Cycle at Global Scale
Strong link between residence times + water pollution
Rates of flow between stores
Snow turning to water vapour / gas
Global Hydrological Cycle
Glaciers / Ice caps
Rivers and Lakes
Store size changes over time for human + Physical reasons.
Warm periods (3mill y'ago)
Climate Warming - Antarctica + Greenland
Water storage reservoirs
Only 2.5% freshwater
only 1% easily accessible.
Water stored in solid form (ice)
Water stored in liquid form (e.g. seas, lakes, rivers etc).
middle of atmosphere
Vegetation + Soil moisture
e.g. The Universe
River/ Channel Flow
Global Distribution of Water
Store 30% of all accessible freshwater
Underground reservoirs of water
Water budgets + River systems
The annual variation in the discharge or flow of a river at a point. (m. in cumecs)
RR Influencing factors
Size of river
Where in course m. taken.
Amount, seasonality + intensity of precip.
^ evap. in summer
Geology + soils
Type of vegetation cover
Compacts soil + removes veg.
Cement, tarmac etc.
Impermeable = increase surface run-off
Decreases river capacity Increases flood level
= fewer natural pipes
Reduce travel distance, channel water directly
Compacts soil + removes vegetation
^ surface run-off
Small basin size
Lack of vegetation
Impermeable rocks e.g. granite
Clay soil (low infiltration)
^ Drainage Density
High water table/ soil saturated with H2O
Large basin size
Permeable rocks e.g. limestone
Low drainage density
Useful indication of
available water supplies
scale, WB's show annual balance between inputs (precip.) + outputs (EVT).
Positive / negative
Precipitation = Evapotranspiration + Runoff ± Storage
Available soil water
Water stored in soil available for growing crops.
Drainage Basin as an Open System
Human Factors influencing DBHC
Domestic + Industrial use
Reduces river flows
for irrigation +
25% of original size
Holds just 10%
Decreases river capacity
Decreases evap. + EVT + capacity
Hold back river flows
^ evap. potential
Changing land use
Surfaces e.g. tarmac, cement etc.
infiltration + percolation
Decreases EVT+ interception + lag time.
Increases surface run-off
Increases flooding potential
^ soil compaction by rain
Over 20% forest destroyed
Legal + illegal
Increased CO2 emissions
Within forests: = 75%
intercepted water returned to atmos. via EVT.
Cleared forest = 25%
Increases interception + infiltration + lag time
Decreases surface run-off
Trees act as carbon sinks
Infiltration 5x greater in forest comp. to grassland.
Without good drainage =
water-logging + salinisation
Installing drainage mitigates this.
Ploughing ^ infiltration = loosens + aerates soil
Silver iodide pellets (ammonium nitrate) = condensation nuclei.
Increases precipitation in drought-stricken areas
Lowers water table
Physical Factors influencing DBHC
Type and amount of precipitation + amount of evaporation
Amount of infiltration, throughflow + type of vegetation (indir.)
Rates of percolation + groundwater flow.
Indir. = soil formation
Rates of interception, infiltration overland flow + transpiration
Area of land drained by river + tributaries
of water into
rocks e.g. carboniferous limestone
e.g. chalk + sandstone
Most likely in
climates w/ vegetated slopes.
lines of concentrated water flow btwn soil horizons to river channel
and natural pipes
of water within the soil layer.
Slow transfer of percolated water through pervious/ porous rocks
Maintains steady level of channel flow in var. weather condits.
Intense, long periods of rainfall
Rapid snow melt
e.g. Arid / Semi-Arid Sahel Region
Prim. agent of
Sheet, gull + gully erosion
River / Channel flow
Flow of water in streams/ rivers
Takes place after water reaches river via OF, TF or GF.
Saturated overland flow
upward movement of
e.g. winter UK 2015, WT rises to surface in depressions + at base of hill sides.
Moisture lost directly into
from water surfaces + soil.
Evap. increases in warm, windy + dry conditions.
From effects of sun's heat + air movement
Factors affecting rate of evap:
(most important factor)
Size of water body
Depth of water
Type of vegetation cover
Colour of surface (
Water lost via
+ transferred to atmosphere.
Factors affecting rate of transp.
Time of year
Type + Amount of vegetation cover
Deg. of availability of moisture in atmos.
Length of growing season
Combined effect of
evap. + transp
Most important aspect of water loss to atmosphere.
Accounts for removal of n. 100% annual
areas. 75% in
in ice fields/ desert areas/ water surfaces/ bare rock slopes. Just evap.
Water loss that would occur if = unlimited supply of water in soil - for use by veg.
Diff. btwn PEVT + EVT greater in arid areas than humid areas.
Type of Precipitation
Land warms up
Air heated above it
Air expands + rises
Air cools + condenses around condensation nuclei = precipitation
When 2 masses of air of diff. temp, humid. + dens. meet.
Rainfall occurs at front of cyclone
Moist air lifted over mountain range
Air cools + condenses as it rises
Orographic clouds form = precipitation
Leeward region sheltered from prevailing rain-baring winds by hill range
influencing Impact on DB
water in DB + fluxes within
Rain, Snow, Hail
^ intensity = ^ risk of flooding
Long Term e.g. Climate Change
Annual/ Seasonal/ Monthly/ Diurnal context
e.g. Localisation of thunderstorm within DB
e.g. in the Nile DB, tributaries start in different
Water absorbed by soil
Capacity decreases with time during rainfall
Antecedent Soil Moisture
^ infiltration in dryer soil. (low ASM)
Permeability of soil
Porosity: Sand/ Silt/ Clay
Type + Amount + Season.
Forest vs. Bare Earth
Density of soil
Compact vs. loose
Shallow = infiltration Steep = surface run-off
H2O stored in plants.
The interception, storage + subsequent loss of precip. via evaporation from canopies.
Wet leaves shedding excess water onto ground surface.
They are larger drops = more erosive power.
Erosive power reduced if leaves = closer to ground.
Flow of intercepted water down stem of plant.
Transfers precip. + nutrients from canopy to soil.
Features of DB
Surface run-off increases as infiltration decreases.
Surface run-off is not a store!