Water Cycle and Security Flashcards
Water budget and changes
- Balance of flux and store
- Changes due to human activity e.g. extraction, reservoirs, climate change
Order of percentage contribution of water stores
Ocean, ice, groundwater, lakes + rivers
Relative importance and size of water stores
- Majority in saltwater storage + inaccessible
- Oceans: 97% of all water
- Atmosphere: clouds, water vapour, precipitation
- Biosphere: all living things inc plants
- Cryosphere: glaciers and ice sheets
- Surface water: rivers, lakes, ponds etc
What are annual fluxes
- Rate of flow from one store to another
- Geographically uneven
- Flux is variable so availability of water varies (arid vs wet)
- Seasonal variation
Precipitation patterns and types (convectional, Amazon)
- Land is hot so air above heats up, expands and rises. Cools as it rises, condensation + clouds. Rains if it continues rising
- High levels at equator w/ convectional at ITCZ, high levels of evapotranspiration
Interception
- Still reaches ground through stemflow and throughfall
- Caused by dense canopy cover, primary barrier to precipitation reaching ground
- Reoccurs with each layer
Infiltration
Water flows through surface of soil and goes through soil pore spaces
Percolation
Continuation of water flow through permeable soil and bedrock
Saturated overland flow
Rainfall is higher than infiltration capacity so it reaches the surface as soil is saturated
Groundwater flow
Transfer of percolated water through permeable rock to a store
Evapotranspiration
- Evaporation - Process by which moisture is lost into the atmosphere from surfaces, soil and rock
- Transpiration - Removal of water through stomata in plant leaves
Channel flow
- Final exit point that water flows through via river or stream
- Discharge measured in cubic metres (cumecs) (m3/s)
Monsoon
- Lasts for 3 months in the summer
- LP ITCZ causes heavy rainfall
- Different atmospheric temp causes difference in pressure between land and sea. HP at sea, so it is cooler. Land has lower specific heat capacity, so heats up faster as temp increases, causing high evaporation + LP. HP moves to LP, changing direction of prevailing wind, moving rainfall in land.
- Plus, Himalayas create relief rainfall
Global water budget
- Reflects balance of precipitation vs evapotranspiration, seasonally and globally
- Base flow is water available, whilst surface flow is seasonal differences e.g. monsoon
Residence times
How long water spends in that store
Fossil water
Confined aquifers - unable to be recharged, as surrounded by impermeable rock
Cryosphere losses
- Reflects climate change and loss means gain in oceans
- Holds 1.9% of all water, 69% of freshwater
Equator and ITCZ
- In spring and autumn, overhead sun. Overhead sun = intense heating = less dense air (evaporation) = bands of heavy rain (condensation as air cools)
- Northern hemisphere summer, sun rays directed above equator
- Winter, rays directed below
Climate affecting drainage basins
- N Sudan precipitation of <20mm per yr, 2,300 in Ethiopian Highlands
- More evaporation in summer esp Sudd Wetlands
- Concentrated in summer as ITCZ migrates north, but small channel flow during rest of year in upstream
Soil affecting drainage basins
- White Nile - clay sediment w limited infiltration + sediment load, so low permeability and limited groundwater storage
- Blue Nile - fertile volcanic silts in monsoons
Geology affecting drainage basins
- Ethiopia: volcanic lavas but very pervious due to weathering
- Uganda: mix of igneous/metamorphic and younger sedimentary
- Sudan/Egypt: sandstone covered by quaternary sediments
Vegetation affecting drainage basins (Nile)
- Nile irrigates Egypt’s crops
- Vegetation density increases south, closer to ITCZ
- More interception + evapotranspiration with monsoon
Relief affecting drainage basins
- Steep topography in Ethiopian Highlands, contributes to higher surface runoff
- Altitude = high levels of weathering, so erosion of dark top soil
Humans disrupt drainage basin cycle
- Can be indirect consequence or deliberate
- Hydrological balance is whether basin can replenish water supply
Deforestation and land use accelerate processes within drainage basin cycle
- Deforestation - output depends on interception vs deforestation
- Changing land use - farming means more caliche, preventing infiltration and dams reduce river flow + floods
Disruption of drainage basin cycle through water abstraction
- To sustain unconfined aquifers, cannot extract faster than rate of recharge
- Water taken out of confined aquifer, so ground is compacted, causing subsidence, water flows overland, contaminating safe water
3 factors of river regimes
Rainfall pattern
Geology (aquifers)
Temperature (evapotranspiration)
River regimes
- Indicate annual variation of discharge
- Simple - one peak, one trough, one climatic zone
- Complex - two climatic zones feeding same river
Impact of climate on river regimes
- Amount and timing of rainfall, depends on amt of climatic zones
- Temperature determines evapotranspiration
- Freezing conditions suspend flow
Impact of geology on river regimes
- Porosity and perviousness of rock, aquifers steadily release water
- Impermeability, water quickly flows through after heavy rain
Impact of soils on river regimes
- Permafrost inhibits percolation and melting increases water supply
- Deep soils store water, so slow release = steady regime
River regime in Yukon River
- Limited evaporation + precipitation = small change in water budget
- Permafrost is impermeable and form of storage
- Spring thaw creates steep spike that gently declines
River regime in Amazon River
- Double regime
- Equatorial (no dry season, heavy convectional rainfall)
- Tropical in south (drier season in winter, highest flow after summer rainfall peak)
River regime in River Nile
- Tropical with distinct drier season and no rainfall in northern areas, creating negative water balance
- Ethiopian Highlands creates large amount of runoff downstream
- Spikier/flashy regime with peak discharge from May to Sep (monsoonal relief rainfall)
Storm hydrograph
- Flashy = short lag time, high peak, steep rising limb
- Flat = long lag, low peak, gentle rising limb
How drainage basin size/shape affects storm hydrograph
- Small and circular = flashy
- Large and elongated = flat
How drainage density affects storm hydrograph
- High density (more streams/rivers per unit area) = flashy
- Low = flat
Density = total distance of tributaries / drainage basin area
How rock type affects storm hydrograph
- Impermeable restricts percolation, encourages surface runoff = flashy
- Permeable = flat
How soil type affects storm hydrograph
- Flashy = low infiltration rate e.g. clay soil
- Flat = high infiltration e.g. sandy soil
How relief (topography) affects storm hydrograph
- Flashy = high, steep slopes for runoff
- Flat = low, gentle for infiltration/percolation
How vegetation affects storm hydrograph
- Flashy = low density, deciduous in winter, low interception
- Flat = dense, deciduous in summer, high interception, high transpiration
How land use affects storm hydrograph
- Flashy = concrete/tarmac surfaces, concentrated areas of buildings
- Flat = rural, minimal impermeable surfaces
How urbanisation affects storm hydrograph
- Flashy = deforestation
- Flat = little urbanisation, natural env, low population density
Meteorological causes of drought (ST precipitation deficit)
- S California below average rain levels from 2013-16
- N California is varied but mostly below average
- Possible cause of SST anomalies
Meteorological causes of drought (longer trends and ENSO cycle)
- 5 periods in last 500 years where snowpack levels have been equivalent to today
- ENSO leads to La Niña which reduces rainfall
Hydrological causes of drought (California)
- California relies on snowmelt water supply
- Snowpack reduced from above to below average (2005, 150% to 2015, 5%)
- 2011 peak, not enough to recover
Meteorological drought
- Low levels of LT precipitation
- No definition of minimum duration of reduced precipitation that makes it an official drought
- Region specific, depends on whether evapotranspiration is high or not
Hydrological drought
- Deficiency of water in surface/subsurface water supplies e.g. rivers, groundwater
- Occurs after meteorological and agricultural droughts, takes time for precipitation deficiencies to affect hydrological system e.g. soil moisture
ENSO Cycle normal conditions
- Trade winds from East to West on surface water (SA to Aus/Indonesia)
- Build up of warm water and evaporation causing LP and convectional rainfall
- Clouds reduce in size when moving to West, causing dry, clear skies and HP
- Cold water upwelling to SA, more nutrients/carbon/fish
La Niña
- Extreme version of normal conditions
- Stronger trade winds
- Severe drought conditions in SA
- High rainfall + possible flooding in Indonesia/Australia
- Crops unable to grow
El Niño
- Trade winds from West to East
- Warm water + evap (LP) in SA, HP clear skies in Aus/Indonesia
- Lower rice crop yield
- Cold water upwelling to West, East loses nutrients
- Fish die out or migrate
Human activity (emissions/deforestation) increasing drought risk in Australia
Deforestation - 90% of vegetation removed since 1800s, adds 2 wks/yr onto drought period
Emissions - anthropogenic GHG emissions add to natural variabilities, climate model evidence
Australia over-abstraction (surface water) increasing drought risk
- 95% of rainfall evaporates from surface water
- 40% of leftovers is diverted for human use
Australia groundwater aquifers increasing drought risk
- Aquifers account for 20% of accessible water and 30% of total water usage
- Abstraction often outweighs recharge
- Concentrated in certain areas of the basin
Ecosystem services
1) Supporting - veg growth, nutrient cycling, carbon + nitrogen
2) Regulating - water purification, flood control, hydrosphere+atmosphere
3) Provision - resources, med
4) Cultural - aesthetics, tourism, SSSIs, heritage
Impact of drought on wetlands
- They’re temp water stores, recharge aquifers, trap pollutants
- Drought means aquatic species die
- Less precip = less infiltration/percolation, less groundwater recharge
Impact of drought on forest stress
- Low levels of transpiration
- Lack of precip = veg dying out, so less interception when precip increases again
- Leads to more infiltration and overland flow
Impact of drought on ecosystem resilience
- Soil erosion removes nutrients so veg difficult to recover
- New water encourages erosion
- Veg can’t establish itself or begin series of succession
Meteorological causes of flooding (Coriolis force)
- Earth rotates, so air moving north/south from equator becomes deflected (instead of moving straight up to poles)
- Deflects right in N hemisphere, left in S hemisphere (when facing respective poles)
- Because of force, winds converge and flow in one direction (jet stream)
- Prolonged with storms
Storms (meteorological) lead to flash flooding
- Intense rainfall, thunderstorm, tropical storm
- Small basin = short lag time
- Ground saturates quickly, saturated overland flow
How does heavy, prolonged rain lead to flooding?
- Mid-latitude depressions queue due to jet stream sinuosity
- UK two bands of rain (warm/cold front)
- Ground is saturated and overland flow
- Above capacity of river, spills over floodplain (worst with impermeable, urban)
Monsoonal rainfall leads to flooding
- Specific heat capacity lower on land, heats up faster = more evaporation
- LP and rainfall then HP to LP from ocean, wind moves clouds inland
Snowmelt causes flooding
Iceland Jokulhaup - volcanoes melt ice sheets
Himalayas - glacial lake outburst flood
Siberia - snowmelt can’t infiltrate frozen ground or stuck behind ice dams that burst
Changing land use in river catchment areas increases flood risk
- Urbanisation = concrete over prairie wetlands, reduced absorption/interception
- > increase impermeability/runoff, excess water in narrow drainage network, flooding 2 reservoirs
- Better transport = RUM = urban sprawl and higher density near coasts and reservoirs
- > Rapid developmt of sub-standard property, more risk
Deforestation increases flood risk
- Grasslands allow water in, replaced by improved pasture
- Woodlands intercept and transpire, roots give good soil structure
- Destroyed by deforestation
Urbanisation increases flood risk
- 75-100% impervious cover (tarmac, concrete)
- 55% runoff (5% deep infiltration, 30% evapotranspiration)
Mismanagement through hard engineering increases flood risk
- Lack of investment in flooding, outdated infrastructure
- Removal of greenspace, property developers resist env restoration
- Officials ignore strict building regulations, mismanagement of building location
Damage to soil from flooding
- Eutrophication, too many algae/plants, decay release CO2, acidic water
- Polluted water degrades aquatic habitats and poison soil ecosystems
Damage to ecosystems from flooding
- Most are flood resilient, help distribute water
- Floods lead to breeding, migration, dispersal
Damage to econ activity from flooding
- Flood insurance and impact on house prices
- Loss of crop/livestock (esp subsistence/developing areas), food prices rise
- Services and business put on hold
Damage to infrastructure from flooding (UK)
- Structural damage, 0.5m deep can wash cars away
- 2m/sec = building foundations collapse and stress on bridges
Damage to settlements from flooding
- Depth linked to mortality (can’t swim)
- Post-flood morbidity (water borne diseases)
Climate change affects precipitation trends
- More intense, further around the world
- Tropics get more, S Africa/S Europe will get less
- N Europe more rain, less snow
How does climate change affect evaporation trends?
- Warming = evaporation over oceans esp Asia and N America
- Counteracted by more cloud cover
- More productive veg = more transpiration
- Less soil moisture
How does climate change affect size of snow and glacier mass?
- Lower duration of snow cover, earlier spring melt
- More river water ST, less LT
- More pronounced in high altitude glaciers
- Negative feedback cycle with albedo effect
Climate change affects amount of permafrost
- High latitude temps increase, permafrost degrades
- Active layer becomes deeper and methane release
- Affects groundwater supply and triggers feedback cycle
Climate change affects soil moisture levels
- Less moisture w more evaporation, depends if counteracted w precipitation
- Groundwater depends on abstraction
How does climate change affect runoff and stream flow?
- 1°C increase = 40% runoff
- Accelerated cycles of intense rainfall but less infiltration
- More droughts in between, lakes/reservoirs drying up?
How over-abstraction, water contamination and industrial water pollution lead to water insecurity (quality)
- 20% of aquifers are over-exploited, 2.5bn depend on groundwater, river withdrawal from dams for energy production
- chemical fertilisers, pesticides = eutrophication
- Waste/chemicals, mining, untreated sewage
- 300 mil in China use contaminated water
How population, living standards and industrial/agriculture cause insecurity (quantity)
- More food esp meat and quality increase
- Growing middle class, larger homes, more cars, so more water + HEP
- Inefficient crop production, large increase in industry, huge groundwater depletion in Mekong Delta
Climate variability and saltwater encroachment causing water insecurity (physical, Israel)
- warm climate, hugh evaporation, less precipitation
- 1.1bn3 of groundwater (irrigation is necessary
- freshwater holds back seawater, removal means intrusion
- coastal aquifer is 20-50m below SL, extraction at 40-70m
Importance of good water supply for economic development (Israel)
- Sanitation, sewage/agricultural runoff into coastal aquifer
- agriculture, desert farming specialists + 5000 tube wells
- Energy supply, settler communities have outages
- Industry, huge tech base, exports of fruit
Importance of water for human wellbeing (Rawabi)
- 2.5bn w improved sanitation
- Water responsible for 10% of disease
Env and econ problems due to inadequate water
- Encroachment means less drinkable, useable, safe water even for animals
- Disproportionate impact on poor, women, children
- Worse health, increased health costs
Potential for conflicts inc transboundary sources and international
- Caused by unequal access/allocation
- Lack cooperative management frameworks, due to control/power imbalance + historical conflict
- Govmts, companies that use products relying on water etc. (interntl)
Conflict between users within a country over local sources (Aus)
- Murray-Darling basin plan 2012, legislation guides gov, regional authorities + communities to sustainably manage basin
- Aim to ensure shared water + return water to river system for RAMSAR ecosystems
- Includes buyback scheme, tax money is used to buy from farmers
- Extraction rules changes, irrigators can use large pumps to extract “env” water
Pros of techno-fix of hard engineering
- Megadams reduce flood risk downstream
- HEP develops regional econ (electricity/exports)
- Water supply for agriculture, industry and people
- Irrigation is possible in water stressed areas
Cons of techno-fix of hard engineering
- Reservoirs displace rural residents
- Hydrological changes downstream + reduced water quality
- Damage to farmland, hits the poorest
- Deoxygination + eutrophication + loss of biodiversity
Hard engineering of water transfers and desalination plants
- Rivers can become better transport arteries, helping regional dev
- Turn seawater into drinking water, expensive + high energy usage, yet haven’t exhausted other water sources
- Intake from ocean kills sealife, concentrated brine sinks and kills marine life
- Vicious cycle, need plants due to CC but they use fossil fuels = GHGs
- Reliable source of water
Sustainable schemes to restore water supplies
- e.g. tube wells, pumpkin tanks, earth dams
- ST solution for developing countries
- Seem to have strong sustainability (affordable, local control/materials, maintainable)
- Might not reach enough ppl
Water conservation
- Grey water recycling, metering, pricing, groundwater recharge schemes
- Try to reduce demand so water resources go further or ensure supply for future gens
Intergrated drainage basin management (Colorado)
- No corruption, env protection, food/water security, convo w users + providers
- Good governance w decentralised decision making, effective regulation + planning that’s appropriate for water use in econ productivity
- ‘90s, basin treated holistically to protect env quality, ensure max efficiency of usage and equitable distribution
United Nations Economic Commission for Europe
- Tri-focus: ecosystems, economies, human societies plus adaptation to CC
- 1999 Protocol on Water + Health - reduce disease, increase sanitation
(Helsinki) Berlin Rules
- 9 principles for all countries approved in 2004
- Intergrated management, sustainability, avoidance of transboundary harm, equitable participation, minimisation of env harm
Water Framework Directive and Hydropower (Berlin)
- Divides water into River Basin Districts, transboundary basins
- 2015 target for good quality and quantity
- Only 50% of EU water was good (not polluted, strong river bed, biological/physical quality)
Causes of and global pattern of physical water scarcity
- Diminishing supply: CC, pollution, competing users
- Competing demands: internal basin conflicts, international issues
- Rising demands: pop growth, econ development
Need management
Why the price of water varies globally
- Commodity: natural resouce has a price
- Raised by govmt to discourage waste
- Physical costs of getting water (infrastructure and its sufficiency)
- Depends on who controls it
- Public: quality standards, investment for infrastructure = low costs, subsidies, resolve conflict
- Private: set prices for profit, competition lowers prices, profit before people and costs more than gov owned/subsidised
Mismatch between water supply and demand
- Supply: people buy off vendors, inflate costs, failure vs freedom to use, management structure (access)
- Demand: high = higher prices by water companies
