Factors Influencing Hydrological System Over Short & Long Term EQ2 Flashcards
1
Q
Define drought and describe the different types of drought
A
- Drought is an extended period of deficient rainfall relative to the statistical multi-year average for a region
4 types of drought:
- Meteorological drought is where long-term precipitation is lower than normal
- Agricultural drought is when there’s not enough soil moisture for enough crops to grow caused by precipitation shortages, and reduced groundwater levels
- Hydrological drought is when the amount of surface & subsurface water is deficient caused by a lack of precipitation.
- Socio-economic drought occurs when water demand outweighs water availability caused by human overuse of sources of water or lack or precipitation.
2
Q
What is ENSO?
A
- El Niño-Southern Oscillation occurs in the Pacific Ocean resulting in more intense storms and droughts from warm water
- Occurs every 2-7 years
3
Q
What is the Walker Cell?
A
- The circulation of air where upper atmospheric air moves E and surface air moves W across the Pacific causing trade winds
4
Q
What is La Niña?
A
- Low pressure over West Pacific becomes lower & high pressure over East Pacific leading to increased rainfall over SE Asia while South America suffers drought.
- Trade winds get stronger due to increased pressure difference between 2 areas.
5
Q
What is El Niño?
A
- Warmer waters develop in the East Pacific with temps rising up to 8°C
- low pressure forms drawing in W winds from Pacific.
- Warm moist air rises —> heavy rainfall over E Pacific
- Air circulates West in upper atmosphere.
- Descending air drier conditions —> drought in Indonesia.
6
Q
What is the SOI?
A
- The Southern Oscillation Index is the strength, direction and speed of the change in air pressure between normal years and El Niño years called ENSO
- Air pressure at West of S America is recorded and subtracted from N Australia to calculate SOI.
- Sharp drop = El Niño imminent
- ENSO and El Niño causes most droughts in E and N Australia.
7
Q
Causes & impacts of droughts in Brazil 2014-2015? (Deficit in hydrological system)
A
Physical Causes of drought :
- Moist air moves in western direction from South Atlantic across the Amazon Basin
- When the moist air encounters the Andes mountain range it’s forced to run south maintaining the flow of moisture around the Basin.
- In 2014, high pressure systems diverted rain bearing winds further north away from Amazon and prevented them from diverting south from the Andes
Impacts of drought on people:
- 4million people seeking water whilst water suppliers were cut off for 3days per week in some towns.
- HEL production was halted leading to further power cuts.
- Brazil’s 17 largest reservoirs were depleted to very low levels some < 1% capacity.
Human Causes of drought:
- Domestic users and farmers used groundwater as rivers were low in SE Brazil
- High fees of $3000 charged by Brazil’s gov for a license to drill a well led to people drilling illegal wells not monitored for water safety
- This causes groundwater levels to shrink
8
Q
What will happen to the Amazon due to deforestation?
A
- Deforestation & less rainfall is decreasing the ability of the rainforest to regenerate leading to the ecosystem becoming less resilient.
- Less forest cover decreased soil water storage affecting weather patterns.
- The Amazon rainforest’s capacity to absorb carbon will reduce
- More wildfires will increase the level of carbon in the atmosphere
- Less rainfall will affect Brazil’s dependency on HEP which generates 70% of its electricity.
9
Q
Drought in Sahel Case study
(Deficit in hydrological system)
A
- Drought in Sahel where the amount of rainfall varies from 100-600mm p/a.
- Between the 1950s - 1980s rainfall declined up to 40% and drought, poverty and civil war in Ethiopia moved people out of Sahel region into marginal land = deaths
- Since 1996, there have been several wet years = opportunity for re-greening to produce farmland.
- Re-greening = trees & bushes are planted alongside other land management schemes.
- Popular in Ethiopia and Niger & thousands of farmers benefit from increasing yields + low cost reforesting
10
Q
Case Study California
(Deficit in hydrological system)
A
- Around 40mill Californians are facing problems due to droughts and in 2014, the Sierra Nevada region exp 3x wildfires due to the ground being so dry.
- Forecasts suggest a 50% chance of mega droughts hitting SW California and 90% chance of 10year drought
Problems are:
- Soil moisture levels declined
- Forested areas gone back to grassland
- High temps and low winter storms made snowpack levels drop in 2015 which is crucial as its meltwater provides 1/3 of water used by cities and farms.
- Groundwater levels fell by 30m between 2011-2015
11
Q
Impacts of droughts on ecosystems? (Amzn rainforest Deficit in hydrological system)
A
- Droughts cause ecosystem stress and tests it’s resilience
- Ecosystem stress is the survival of ecosystems which can be drought (physical) or pollution (chemical) or diseases (biological)
- Ecosystem resilience refers to the capacity of an ecosystem to withstand pressure from stress.
- The Amazon rainforest has 400billion trees,
- Takes up 20billion tonnes of water vapour daily from the forest & converted as rain on S Brazil.
- Drought =stress = younger trees dying which reduces water vapour and rainfall
- Drought causes dying vegetation to catch fire from sunlight as there’s no water = very harmful to environment
- High winds turn these small fires into wildfires & increased drought = smaller trees.
12
Q
Wetland ecosystems
(Deficit in hydrological system)
A
- Wetlands are areas of where the soil is frequently waterlogged by fresh/salt water
- Wetlands support nutrient cycling and food chains providing fisheries and regulates flood control providing aesthetic value.
Impacts on the Pantanal wetland area:
- Pantanal is 14,000km sq and is a freshwater ecosystem surrounded by seasonal rainfall so aquatic and bird life there depends on permanent wetland for survival.
- But the drought reduced habitats for wild animals and wildfires became a major threat because cattle ranchers set old grass on fire in dry seasons which spreads
13
Q
Meteorological causes of flooding in the UK
A
- Low air pressure causes mid latitude depressions leading to much flooding in the UK
- Showers are brought on the warm front and rain is brought on the cold from
- Prolonged rain = saturated ground = precipitation turns into runoff = quicker movement to river channels = increased river flow
- Flooding happens because too much precipitation exceeds the capacity that can be carried away by a normal drainage system
- Water breaks banks and flows onto floodplain and this happens when the jet stream is hovering around mid latitudes
14
Q
Monsoons in SE Asia
A
- Monsoons (heavy rainfall) in SE Asia is caused by a seasonal change in the direction of prevailing winds & summer monsoon Apr-Sep = heavy rainfall
- Warm moist air from Indian Ocean blows to Indian subcontinent = humid climate as ITCZ moves N & low pressure further N bringing avg 70% rainfall in 100days
- People can increase flood risk by deforestation and urban development increasing surface runoff and by poor maintenance of rivers.
15
Q
Case Study Storm Desmond 2015
(Surpluses within hydrological system)
A
- Storm Desmond = caused by deep Atlantic low pressure system of rain = a depression
remained over NW for long bringing rain depressions from across the Atlantic. - Human causes = mismanaging rivers by new raised riverbanks and diverted channels carrying surplus water after away from built up areas in Cumbria costing £400-500million from flooding in 2015
- Keswick’s flood defences were built to allow the river to rise to 5m but in 2015 the river rose to 5.9m overtopping new defences.
The impacts were:
- 5200+ homes flooded in 2015
- Schools & healthcare closed temporarily
- 61000 homes lost power
- Repeated flooding deterred tourists
- River banks eroded —> future flood risk
- Habitats destroyed + ecosystems affected
Mitigation:
- Env agency recommends soft engineering methods for Cumbria to adopt in the future
- Restoration of river channels and floodplains to their natural state to store floodwater
- Planting trees again to reduce rapid surface runoff
