Miss McDonald EQ2 (ON SPEC) Flashcards
Meteorological drought
Degree dryness compared ‘normal’ precipitation
Agricultural drought
Insufficient water for crops so that they wilt without irrigation
Hydrological drought
Where drainage basins suffer shortfalls
Global atmospheric circulation
-low pressure=warm air rises+cools forming precipitation
-high pressure=cool air falls+warms surface bringing clear skies no rainfall
E.g. ‘sub tropical’ band 30degrees N/S air risen equator cooled+sinks forming belt high pressure hot,dry conditions
ITCZ
- Belt low pressure(rain) migrates W/seasons 23degrees N/S or 0- alternating wet+dry seasons
- may fail blocked high pressure from descending part Hadley(high pressure) or loops jet streams occasionally break up allowing high pressure from subtropics move N+ block bringing droughts mid latitudes (UK)
ENSO
El Niño+ La Niña(opposite) shift rainfall patterns
- El Nino brings warmer water to America’s reducing rainfall W pacific
- la Nina brings warmer water to extreme W of tropical pacific reducing rainfall W americas
Flooding UK-jet stream+ low pressure weather
As Mid latitudes=boundary zones polar+tropical air masses where jet steam formed-brings low pressure(frontal rain)by meeting warm+ cold air+uplift condensation
Sometimes high pressure blocks jet stream+ continually delivers low pressure to 1area high pressure either side
Flooding India-monsoon
Intense seasonal rainfall-widespread damaging flooding
Around 70%annual avg rain 100days July-Sept, 80%Bangladeshi ppl affected, 1/2 country less 12m above sea lvl, low-lying plains largest rivers most at risk along river courses+at edge delta
Flooding Siberia-Ice melt
- Siberian snow melt spring causes extensive flooding across interiors Asia e.g. River Ob
- Quick transition winter-spring upstream causes rapid snow melting while lower reaches remain frozen W/v limited infiltration
- Flood water often held up temp ice dams
- Sometimes rain falls melting snow when rapid thaw occurs-> this combo can cause heavy flooding
Physical primary meteorological causes Cumbria floods 2015
- flooding happened 3rd time 2015 in a decade 2005,2009+2nd wettest nov since 1910
- moist air mass stayed over Cumbria up to 48hrs delivering records amount rain
- jet stream remained over N longer usual normally moves N+S brought low pressure (rain) from across Atlantic thru ‘conveyor’ warm+v moist air from Caribbean where sea temps unusually high
- Cumbria= wettest seathwaite avg 2mrainfall/yr
Secondary causes for Cumbria floods 2015
- steep slopes Cumbria Mountains helped steer run rapidly into river (orographic rainfall)
- ground already saturated from previous antecedent conditions meant additional rain flowed surface run-off straight into rivers
- rivers Derwent+Cocker= already swollen W/ previous rainfall
- impermeable rock type Lake District impeded infiltration
- Cockermouth built confluence 2rivers making susceptible flooding after heavy rains
Soc impacts Cumbria floods 2015
- 3000homes flooded 2005+5,200 2015
- 40skls closed
- routine business across NHS hospitals cancelled
Econ impacts Cumbria floods
- UK dented as much £3bn damage storms Eva, Desmond+ Frank
- insurance claims caused flooding 2015 exceeded £6bn
- house prices fell flood-risk areas
Environ impacts Cumbria floods
- river chocked W/debris+contaminated sewage+ effluents+ pollutants
- saturated ground-decomposition dead plants+animals giving off noxious gases- contaminated food chains+threatened wild life
- soils=eroded habitats destroyed+ecosystems destroyed
How climate change might affect drainage basin if drier than normal
- Decreases precipitation 10-30degrees N+S equator(inputs)
- initial high rates evaporation followed lower lvls when available water falls+EVT decrease as less soil moisture affecting veg as outputs
- reduce lvl water stored soil, rivers+lakes causing increased reliance+use groundwater W/more humidity+ increased drought severity+freq
- Increasing high pressure zones e.g. subtropics+ drier soils altho more intense rainfall events
How CC might affect drainage basin if wetter than normal
- inputs increase->Increase soil moisture more stored rivers+lakes W/no reliance+ less use groundwater, cause more evaporation+ convection increasing risk flooding as more saturated ground more surface run off
- 1degree rise temp-could increase global runoff 40%
- Overall decreased snow, permafrost+ice cover as stores initially increased meltwater increasing river floods but decreasing long-term
Impacts CC Sahel
- possible change climate since 1996 7wet yrs in between droughts + opportunities re-greening
- planting trees+ bushes along other schemes so regeneration water retaining veg low cost, water harvesting tech also stone lines built Burkina Faso retain moisture (traps)
- if works increase inputs naturally+evaporation+EVT from veg- more storage rivers,lakes+ soil W/more runoff+stream flow
- but rainfall extremely variable 100-600mm/yr+ rains might fail W/CC if tropics warm up, ITCZ won’t migrate as far N+ ‘summer’ rains will fail so uncertainty
Impacts CC California
- fall precipitation+rise temp-increase evaporation rates, surface runoff+ soil moisture lvls decrease forested areas reverted scrub+grassland
- relying groundwater fallen 30m 2011-15
- reservoir lvls fallen Oct 2016 water storage 77%avg time of yr
- permanent snow lvls 2015=record low due high temps+ lack winter storms crucial coz meltwater=1/3water used Cali cities+farms
- forecast suggest 50%chance mega droughts hitting SW Cali +90% decade long drought
- worsening situation BUT uncertainty if mitigation (help/schemes) not as dry
Uncertainty of future CC projections
- complexity of climate systems
- natural short-term oscillations e.g. ENSO brings insecurity +sunspot cycles
- bio geochemical positive+feedback systems
- incomplete set date (not collected all locations+as detailed)
- no clear evidence flooding getting bigger+more frequent
- many other factors increase pop riskier locations, land used changes, rising pop, poor farming+normal variability
- don’t know where+ how much
Concerns over water security
- every 1degrees temp rise amount moisture held atmosphere increase 7% potential heavier precipitation W/2010 wettest yr
- change precipitation, temp+ potential ET severity+occurrence droughts rise
- more intense droughts affects more ppl Australia+ spreading new areas S EU, SW USA+ Sahel
Intense storms cause floods
Severe storms e.g. tropical cyclones Bring lots rainfall short time moving quickly into channels unable soak into ground causing overflow
In arid+semi occasional thunder drop lots rain suddenly runs quickly over baked ground- ‘flash’ flood
Heavy rainfall causing floods
Lots rain short time perhaps caused cold front in low pressure system- too much allow through flow/ groundwater flow take place so excess water quickly runs off surface +into river channels where discharge increase to flood lvls
Prolonged rainfall causing flooding
Persistent rain long period perhaps result 7 low pressure systems passing over area- sequence frontal rainfall
First soil saturated so later rainfall can’t infiltrate
Runoff increased+ quickly enters river channels causing floods
Other factors about Sahel
25%drop agricultural production since 2010, rise 20-60% food prices past 5yrs, 15.6m ppl affected Sahel
Human causes Sahel drought (CS) 2012/13 animals
Increase animals some areas livestock 40% pluvial yrs(water) before mid 1960s-overgrazing soil depleted nutrients, land stripped protective grass cover so veg can’t re-est-desertification
Human causes Sahel drought (CS) 2012/13 pop
- pop growth from more immigrants (refugees civil wars+droughts) increasing demand wood cooking+heating+building especially urban areas-deforestation (mainly fuel wood)-veg removed increasing erosion+evaporation-desertification
- pop growth high birth rates+ lowering death rates w/annual growth rates 2.5-4% farmers forces change trad land use->more needed food+ cash crops- over cultivation: reduced soil fertility, soil left exposed rain+ wind- desertification
Impacts of droughts wetlands (Florida) explain
- wetlands=not resilient drought owning reliance submergence water prolonged time
- drough major impact limited prec, less interception as veg deteriorate+less infiltration+ percolation groundwater stores- water table fall
- process evaporation continue+ might increase from less-protected surface while transpiration rates decrease-wetland less functional+ desiccation can also accelerate destruction wild fires
Impacts of droughts on wetlands (Florida) services environ
- supporting ecosystem-primary production energy net rated 1,000gC/m^2/yr (1/2 rainforest which= most), nutrient recycling, food webs, carbon store!
- regulate water- flood control absorb excess water (+storm surges) prec release slowly back protecting shorelines+ plant species anchor soil w/roots, groundwater recharge areas, purifies water plant species absorb excess nitrogen+ other pollutants
Impacts of droughts on wetlands (Florida) services human
- providing- fuelwood+peat, fish mammals+ birds
- aesthetic beauty from plant species
- recreation (hunting, bird watching fishing) cultural value
- econ value breeding grounds many aquatic animals provide us w/food +7 food plant species= dependent on wetlands
Impacts of droughts on forests (Cali) natural function human+environ
- gds timber food etc
- soc+cultural benefits recreation, spirituality
- carbon storage calc avg 0.73tonnes/hectare/yr(important regulating CC)
- nutrient cycling, water+air purification+maintenance habitat species, soil preservation
Impacts of droughts on forests (Cali) resilience
- not resilient drought some species tree lower resilience+drought stressed tree-foliage loss impairing growth
- increasing accumulation pests+diseases+ damage vascular tissues impairing water transport
Impacts of droughts (Cali) recent yrs
-droughts getting worse recent yrs destruction+size W/CC all but 1/10 biggest forest fires past 2 decades, drier warmer conditions-veg dying out+more flammable+ drying out soils lowering water table reduces natural protection (CC) + winter seasons rain/snow shorter
Human factors increase flood risk (freq+mag) pop
- pop growth-> land use changes+ urbanisation
- urbanisation rural urban migration creation impermeable surfaces increases surface runoff 60%residents ldn paved front garden
- dams reduce discharge downstream, drains/sewers reduce lag time, impending flow building alongside W/bridges narrow channels high water lvls downstream+ levees
- deforestation woodlands lost=intercept rain+transpire moisture+roots-gd soil structure
Human factors increase flood risk (freq+mag) management
-poor river management-straightening channels(realignment)increase flow+ risk+ resectioning by dredging widening+deepening increase capacity faster movement+channelisation removes marshy areas
Human factors increased flood risk (freq+mag) agriculture
- Land use changes (increased pop) w/agricultural development-> deforestation, overgrazing, ploughing/ drowning wetlands usually occuring upstream knock on effect down stream
- increased run-off +lvls sediment can block river channels downstream, grazing animals trample soil+ ploughing compacts-> increased run-off+ sprinkling groundwater onto arable crops
Human factors increased flood risk (freq+mag) pol
-econ+pol budget cuts flood defences, green priorities EU Water Framework Directive puts environ concerns before regular maintenance+ advocates making space flood lowlands, poor land management blocking+econ growth building flood plains+ modifying landscapes
