Water cycle influences

T5 - Water

types of drought

• meteorological

• agricultural

• hydrological

• socio - economic

meteorological drought

a degree of dryness compared to waist is considered to be normal precipitation

• for that area, climate, season

agricultural drought

insufficient water for crops

• leads to wilting/loss of crops without irrigation

hydrological drought

the drainage basins suffer shortfalls

• e.g. reduced streamflow

• inc. river flow into reservoirs

socio economic drought

demand for water to be used for social and economic purposes exceeds water availability

• for uses e.g. HEP, crop irrigation

physical causes of drought

• ENSO cycles

• short term precipitation deficit

short term precipitation deficit

occurs when the cycle that makes clouds is interrupted

• may occur in areas of low pressure, suddenly experience high pressure system

• cool sinking air in high pressure = cannot form clouds and form precipitation

ENSO cycles

El Niño southern oscillation

• the El Niño and la niña changes in the Pacific Ocean

ENSO - la niña

• low pressure on SE Asia and Australia = inc. rainfall and flood risk

• high pressure in S america = red. rainfall, inc. drought risk

ENSO - el nino

• every 3-5 years

• wind weakens and reverses direction - across South Pacific

• warm water moves to S America coastline = low pressure - inc. rainfall and flood risk

• high pressure in Australasia due to cooler water = little rainfall - inc. drought

ecosystem functioning

the biological, chemical and physical processes that take place in an ecosystem

ecosystem resilience

how capable the ecosystem is of surviving changing water levels

• deserts/semi arid areas are most resilient to drought

impacts of drought - rainforest

• leads to forest stress

• younger trees die - reduces canopy cover

• less interception and infiltration

• dec. evaporation - water vapour and rainfall reduces

impacts of drought - forests

• can set alight - if sunlight is on exposed dead vegetation and dry organic material

• high wind/lightning storms - can turn fire into wildfire

• e.g. Croatia 2017 - wildfire after 2 ½ months of drought

impacts of drought - wetlands

• inc. likelihood of tree mortality

• dec. in veg. - reduces anima habitat

• can eliminates species - effects food chain and communities

• inc. chance of wildfire

• e.g, Suffolk - wetland thrush impacted by dry soil, can penetrate soil to reach food

human causes of flooding

• urbanisation

• vegetation removal

• floodplain drainage

• agriculture

• river management

human causes of flooding - river management

• meant to provide flood protection - can do opposite (esp. hard engineering)

• chanelisation and river straightening can inc. flood risk

• levees and man made channels can restrict the river = more likely to burst banks

channelisation

the widening or deepening of a river

• to improve hydraulic capacity

river straightening

modifying rivers course by removing a rivers meanders to create a straighter path

• inc. speed of water flow and reduce flood risk ( harder for water to build up ad flood)

human causes of flooding - agriculture

• food demand inc. = agricultural demand inc. - farms often on deforestation sites

• agcritulutre inc surface runoff and soil exposure - causes erosion, transports sediment to rivers

• sediment reduces rivers carrying capacity - inc. likelihood of bank bursting

human causes of flooding - floodplain drainage

• floodplain = flat and fertile - desirable for agriculture

• often drained to prevent floods - destroys habitats

• can shrink and lower area - inc. likelihood of flood

human causes of flooding - vegetation removal

• dec. ground cover = less interception

• reduces infiltration

• leads to inc. surface runoff

human causes of flooding - urbanisation

• removal of vegetation - inc. surface runoff

• inc. of impermeable surfaces - no infiltration - inc. runoff

• runoff enters drainage system, takes water to rivers and waterways - reduces lag time, causes high peak discharge

meteorological causes of flooding

• flash floods

• prolonged/heavy rainfall

• extreme monsoon season

• snowmelt

• ENSO - la nina

meteorological causes of flooding - ENSO La Niña

• change in weather across South Pacific ocean

• exaggerates normal weather

• warm water and low air pressure to Australasia - inc. rainfall and flood risk

meteorological causes of flooding - snowmelt

• temp inc. after winter - snow melts

• evident in mountain env.

• inc. runoff and flash floods

meteorological causes of flooding - extreme monsoon rainfall

• monsoon = seasonal change in direction of prevailing winds as ITCZ moves north

• wet and dry seasons in subtropical areas near oceans

• india and SE asia at risk

• leads to extreme rainfall

meteorological causes of flooding - prolonged/heavy rainfall

• caused by mid latitude depressions

• heavy rain = saturates soil, stops infiltration and increases runoff

• water reaches channel quicker - causes flooding

meteorological causes of flooding - flash flooding

• happens quickly and frequently without warning

• low air pressure systems - can create intense tropical storms that produce heavy rainfall

mid latitude depressions

low air pressure systems that produce a lot of rain

• 2 air masses meet, 1 hot 1 cold - cold pushes hoy up, leads to cooling

• condenses and forms rain

environmental impacts of flooding

• ecosystems

• soils

environmental impacts of flooding - ecosystems

• can destroy plants beyond use/ uproot them and break into pieces in river channel

• can destroy farmers harvest - need to restart

• animals dependent on habitat/agriculture at risk - have to migrate or compete for resources

• can lead to species decline

environmental impacts of flooding - soils

• sediment from banks/river beds eroded during flooding

• can block sections of a river or underground waterworks

• soil erosion of fertile soil e.g. amazon

socio economic impacts of flooding

• economic activity

• infrastructure

• settlements

socio economic impacts of flooding - settlements

• flooding of power stations can impact homes

• home flooding

socio economic impacts of flooding - infrastructure

• long term/temporary inability to use infrastructure

• e.g. roads, railways, bridges

socio economic impacts of flooding - economic activity

• can close businesses - infrastructure damage

• business owners lose productivity and income - workers cant come in

• damaged shops may lose their stock

• insurance companies have to pay out

climate change effects

• precipitation trends

• evaporation trends

climate change effects - evaporation

• inc. in temp = inc. evaporation

• dec. in temp = dec. evaporation

• temp dec. below freezing = water remains frozen - stored as ice

climate change effects - precipitation

• inc. precip. = inc. flooding/ ecosystem change

• tropical storms more likely = sea level and temp rise

• higher rainfall - coastal flooding

• can reduce precipitation

CC effects on stores/flows

• permafrost

• snow/glacier

• soils

• reservoirs/lakes

CC effects on stores/flows - reservoirs/lakes

• not recharged as much - dec. in rainfall and higher temps.

• impacts local ecosystem and residents

• e.g. lake chad

CC effects on stores/flows - soils

• different soils in dif. climates affect by GW differently

• soil moisture dec - as less infiltrate in droughts/intense rainfall due to high runoff

CC effects on stores/flows - snows and glaciers

• inc. in avg global temp

• reduction in ice forming seasons

• 2018 - smallest arctic ice since 1960s

• ice not forming to same extent - current ice breaking off in large icebergs

CC effects on stores/flows - permafrost

• can thaw in summer - leads to percolation and through flow until water left ecosystem

• CC leads to rise in temp - soil temp inc. - more permafrost loss

CC uncertainty

increases uncertainty

• ENSO

• drought risk projections

• flood risk projections

CC uncertainty - flood risk

• SE asia - inc. in flooding

• Bangladesh - 70% floodplain, rest 1m above sea level

• sea level rise + tropical storms = flood risk for Bangladesh

• himilayan glacial meltwater inc = river flooding

CC uncertainty - drought risk

• at risk - USA, Central America, mediterranean = dec. in rainwater

• south med. - more at risk due to high pop, reliance on tourism

• red. risk - north Alaska, asia

CC uncertainty - increasing

• CC inc. uncertainty of weather

• higher/lower precipitation - causes flood/drought

• sea level rise, warmer temp - inc. tropical storms + floods

CC uncertainty - ENSO

• produces uncertainty for weather patterns

• el nino = wind decline/reverse - warm water moves towards SA - inc. rainfall+flood

• la nina = exaggerate weather - inc. drought SA, inc. flood Australasia

drought

when there is a water deficit in a particular place over a period of time

• compared to average rainfall for the same period

tipping point

when system changes from one state to another

positive feedback

a cyclical sequence of events that amplifies or increases change

negative feedback

a cyclical sequence of events that damps down or neutralises the effects of a system

flood return period

a statistical estimate of how often flood of a certain magnitude is likely to occur

• based on past flood levels

• e.g. 1 in 50 year flood or 1 in 100 year flood