Physical - Water Cycle Flashcards
Meteorological drought
- Defined by shortfalls in precipitation as a result of short-term variability within the longer-term average overall, as shown in many semi-arid and arid regions such as the Sahel
- Drought has becomes almost a perennial problem in recent years as longer-term trends have shown a downward movement in both rainfall totals and the duration and predictability of the rainy season
Major features of meteorological drought
Rainfall deficits
- Low precipitation
- High temperatures
- Strong winds
- Increased solar radiation
- Reduced snow cover
Major impacts of meteorological drought
- Loss of soil moisture
- Supply of irrigation water declines
Agricultural drought
The rainfall deficiency from meteorological drought leads to deficiency of soil moisture and soil water availability, which has a knock-on effect on plant growth and reduces biomass
Major features of agricultural drought
Soil moisture deficit
- Low evapotranspiration
- Plant water stress
- Reduced biomass
- Fall in groundwater levels
Major impacts of agricultural drought
- Poor yields from rain-fed crops
- Irrigation systems start to fail
- Pasture and livestock productivity declines
- Rural industries affected
- Some government aid required
Hydrological drought
- Associated with reduced stream flow and groundwater levels, which decrease because of reduced inputs of precipitation and continued high rates of evaporation
- It results in reduced storage in lakes and reservoirs, often with marked salinisation and poorer water quality
Major features of hydrological drought
Stream flow deficit
- Reduced infiltration
- Low soil moisture
- Little percolation and groundwater recharge
Major impacts of hydrological drought
- Reduced storage in lakes and reservoirs
- Less water for urban supply and power generation - restrictions
- Poorer water quality
- Threats to wetlands and wildlife habitats
Famine drought
A humanitarian crisis in which the widespread failure of agricultural systems leads to food shortages and famines with severe social, economic and environmental impacts
Major features of famine drought
Food deficit
- Loss of natural vegetation
- Increased risk of wild fires
- Wind-blown soil erosion
- Desertification
Major impacts of famine drought
- Widespread failure of agricultural systems
- Food shortages on seasonal scale
- Rural economy collapses
- Rural-urban migration
- Increased malnutrition and related mortality
- Humanitarian crisis
- International aid required
Example of a humanitarian crisis in relation to famine drought
Horn of Africa, 2012-14, required international solutions
Desiccation
The removal of moisture from something, i.e. cracked land
What % of the Earth’s land area has been affected by drought in the last 30 years?
30%
Palmer Drought Severity Index (PDSI)
- Applies to long-term drought and uses current data as well as that of the preceding months, as drought is dependent on previous conditions
- It focuses on monitoring the duration and intensity of large-scale, long-term, drought-inducing atmospheric circulation
Crop Moisture Index (CMI)
This is a measure of short-term drought on a weekly scale and is useful for farmers to monitor water availability during the growing season
Palmer Hydrological Drought Index (PHDI)
The hydrological system responds slowly to drought, both in reaction to drought and recovering from it, so different models need to be developed for rivers, lakes, etc.
ENSO cycles - normal year
- Trade winds blow equator-wise and westwards across the tropical Pacific
- Winds blow towards the warm water of the western Pacific
- Convectional uplift occurs as the water heats the atmosphere
- Trade winds push warm air westwards. Along the east coast of Peru, the shallow position of the thermocline allows winds to pull up water from below
- This causes upwelling of nutrient-rich cold water, leading to optimum fishing conditions
- The pressure of the trade winds results in sea levels in Australasia being 50cm higher than Peru and sea temperatures being 8°C higher
- The Walker loop returns air
ENSO cycles - El Niño year
- Trade winds in the western Pacific weaken and die
- There may even be a reverse direction of flow
- The piled-up water in the west moves back east, leading to a 30cm rise in sea level in Peru
- The region of rising air moves east with associated convectional uplift. Upper air disturbances distort the path of jet streams, which can lead to teleconnections around the world
- The eastern Pacific Ocean becomes 6-8°C warmer. The El Niño effect overrides the cold northbound Humboldt Current, thus breaking the food chain. Lack of phytoplankton results in a reduction of fish numbers, which in turn affects fish-eating birds on the Galapagos Islands
- Conditions are calmer across the whole Pacific
Teleconnections
In atmospheric science, refers to climate anomalies which relate to each other at large distances
ENSO cycles - El Niña year
This is an exaggerated version of a normal year, with a strong Walker loop
- Extremely strong trade winds
- The trade winds push warm water westwards, giving a sea level up to 1m higher in Indonesia and the Philippines
- Low pressure develops with very strong convectional uplift as very warm water heats the atmosphere. This leads to heavy rain in southeast Asia
- Increase in the equatorial undercurrent and very strong upwelling of cold water off Peru results in strong high pressure and extreme drought. This can be a major problem in the already semi-arid areas of northern Chile and Peru
The Sahel
- Semi-arid
- Stretches across the African continent from Mauritania to Eritrea
The Sahel - seasonal climate
- It occupies a transitional climate zone, so is drought sensitive
- The mean annual rainfall of 85% is concentrated in the summer
- It varies from 100mm (edge of Sahara) to 800mm (southern margins)
The Sahel - annual climate
- Huge variabiltiy from year to year, especially on the Saharan fringe
- Unusually warm sea surface temperatures in tropical areas favour strong convectional uplift over the ocean that in turn, weakens the West African monsoon and contributes to drought in the Sahel
Example of drought in the Sahel
1999-2000 Ethiopian-Eritrean drought/famine crisis, 10 million people needed food assistance
Climate change - ST/LT
ST - less rainfall, increased drought
LT - global warming: higher temperatures, increased evaporation, reduced condensation
What does overgrazing lead to?
Soil will be depleted of its nutrients and land stripped of its protective grass cover
What does overcultivation lead to?
Reduced soil fertility, soil left exposed to rain and wind
Drought in Australia
- Serious deficiency - rainfall totals within 10% values record for at least 3 months
- Severe deficiency - rainfall totals within the lowest 5% of values on record for at least 3 months
- Caused by major physical reasons: low, highly variable rainfall due to sub-tropic high pressure belt of the southern hemisphere; droughts vary considerably in terms of length; most events are linked with El Niño events; some events are thought to have been caused by climate change
When did the Big Dry happen in Australia?
2006
Drought event in Australia linked with El Niño?
East Coast drought of Southern Queensland in 2002-03
When did Australia start to see a change in shift in rainfall patterns?
1970s - eastern area = drier, compared to north-western areas
What % of Australia is affected by drought in any one year?
30%
What % of Australia’s agricultural outputs are provided by the Murray-Darling Basin?
50%
Following the Big Dry in Australia, reservoirs fell to what % of their capacity?
40%
Which city in Australia was made vulnerable due to the Big Dry?
Adelaide, this is because it drew 40% of its drinking water from the River Murray
What schemes has Australia developed to combat drought events?
- Desalination plants
- Large-scale recycling of grey water and sewage
- Strategies for water conservation (i.e. smart irrigation for agriculture)
Wetland
An area of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt
What % of the Earth’s land surface do wetlands cover?
10%
Key functions of wetlands
- Act as temporary water stores within the hydrological cycle, this mitigating river floods downstream, protecting land from destructive erosion by acting as washlands, and recharging
- Chemically, they act as large water filters, trapping and recycling nutrients and pollutants - maintains water quality
Ecosystem services of wetlands - supporting
- Primary production at a very high level
- Nutrient cycling
- Food chain support
- Carbon state within
- Life support systems of carbon cycles
Ecosystem services of wetlands - regulating
- Flood control
- Groundwater recharge/discharge
- Shorelines as change and to protect
- Water purification
Ecosystem services of wetlands - provisioning
- Fuelwood, peat
- Fisheries
- Habitats for mammals and birds - also attracts tourism
Ecosystem services of wetlands - cultural
- Aesthetic value
- Recreational use
- Cultural heritage
Impact of drought on wetlands
- Limited precipitation leads to vegetation deteriorating
- This leads to less interception, and less infiltration and percolation to the groundwater stores, leading to water table levels falling
- Evaporation will continue and might increase from less-protected surfaces
- Transpiration rates will decrease, making wetlands less functional
- Desiccation will accelerate the destruction by wildfires
How many sq km of wetlands have been destroyed in Europe and the USA for agriculture and urban development?
2.5 million sq km
Schemes that have led to wetland drainage
- Jonglei Canal Project, which diverted the White Nile discharge away from the Sudd Swamp to the dry land areas of South Sudan
- Degradation of the Okavango Delta in Bostswana for cattle rearing
- Marshland of Southern Iraq has been destroyed by dams on the Tigris and Euphrates, as well as being drained by Saddam Hussain’s Drainage schemes
How many lives were destroyed following Saddam Hussain’s drainage schemes?
250,000
Name a wetlands convention
1991 Ramsar Convention on Wetlands, it has listed over 1800 wetlands of international importance (covering 1.7 million sq km in 160 states)
Environments at risk of flooding
- Low-lying parts of flood plains and river estuaries, which are also at risk of groundwater flooding
- Low-lying areas with urbanisation are at risk of surface water flooding after periods of intense rainfall
- Small basins, especially in semi-arid/arid areas, are subject to flash flooding
Groundwater flooding
Flooding that occurs after the ground has become saturated from prolonged heavy rainfall
Surface water flooding
Flooding that occurs when intense rainfall has insufficient time to infiltrate the soil, so flows overland
Flash flooding
A flood with an exceptionally short lag time - often minutes or hours - usually associated with very intense convectional storms
Climatological causes of floods
- Rain
- Snowmelt
- Icemelt
- Combined rain and melt
Part-climatological causes of flooding
- Estuarine interactions between streamflow and tidal conditions
- Coastal storm surges
Other causes of flooding
- Earthquakes
- Landsides
- Failures of dams and other control works
UK flooding
- Usually from prolonged and heavy rain associated with the passage or low-pressure systems or depressions
- The traditional time of year for this sequence, known as a progressive cycle, is autumn or early winter but, as a result of unusual positions in the jet stream, this sequence can occur at other times of year
- The degree of flooding depends on the precise depression sequence - sometimes a succession of very intense storms
Flooding events in the UK
- 2007-08 summer floods
- October-December floods of 2015 - resulted from a sinuous jet stream in a fairly constant track, which means that all high-pressure systems (anticyclones) were ‘blocked’
What % of the average annual rainfall occurs over 100 days (July-September) during monsoon season?
70%
During monsoon season, which areas are most at risk of flooding?
The low-lying plains of the larger rivers in India, Pakistan, Bangladesh, Vietnam and China
What % of Bangladeshi people are exposed to flood risk?
80%
Pakistan floods
- July 2010
- 9000mm of water was received in one week, which was about 10x the year average
- Caused local flash floods, and landslides also contributed to flooding on all major rivers downstream
What year was there flooding in Mozambique?
2000 - regular rainfall was supplemented by tropical cyclones
Which north-flowing Siberian rivers caused flooding from snow and ice melt?
Rivers Ob and Yenisei
What drains the glacial lakes of the Himalayas?
Glacial outburst floods, which occur as ice dams melt
Why do glacial outburst floods happen in Iceland?
Volcanic activity, which generates melt water beneath the ice sheets and acts as a trigger for ice instability
Which factors determine the impacts of flooding?
- Vegetation - greater cover means more interception, storage and evapotranspiration, which reduces rainfall and increases the lag time
- Slope - steeper-angled slopes mean less water in absorbed and more runs off
- Rock type - permeable rock allows greater infiltration and ground storage, leaving less water to run off
- Soil depth - deeper soil absorbs more water and results in less run-off
- Drainage density - total length of streams (km), total drainage basin area (sq km) - where the drainage density figure is low, there is a longer lag time and a reduced risk of flooding
Human causes of flooding
- Ploughing compacts soil
- Grazing animals trample soil
- Natural streams meander and have marshy areas; channelisation does not
- Woodlands intercept rain and transpire moisture; roots give good soil structure. This is destroyed by deforestation
- Natural grasslands allow water to sink in, replaced by improved pasture - destruction
- Bridge supports built in rivers, ramps on floodplain
- Dams built to supply water to towns
- Sprinkling of groundwater onto arable crops
- Wells sunk into settlements
- Urbanisation creates impermeable areas
How has urbanisation contributed to flooding
- Creation of impermeable surfaces
- Speeding up the drainage of water in built-up areas via artificial conduits (drains, sewers)
- Straightening of channels to increase flow, which causes flooding downstream
- Land-use changes - deforestation, agricultural development
From 1990-2010, the Emergency Events Database (EM-DAT) recorded how many flood disasters worwide?
3000
From 1990-2010, the Emergency Events Database (EM-DAT) recorded how many deaths caused by flooding disasters worldwide?
200,000 deaths
From 1990-2010, the Emergency Events Database (EM-DAT) recorded how many people being affected by the flooding disasters worldwide?
3 billion people were affected
How many people worldwide live in areas prone to flooding?
900 million people
How many people worldwide are exposed to flooding every year?
75 million
What percent of all flood deaths and economic damage occurs in Asia (notably China, India, Bangladesh, Pakistan and Vietnam)?
90% of all flood deaths, 50% of all economic damage
How much did the UK floods of December 2015 cost?
£1.3 billion
How much are annual flood losses in Australia?
A$372 million
What velocity of water can cause foundations of buildings to collapse?
2m per sec
What groups of people are vulnerable to flooding events?
Elderly, children
Secondary flood hazards?
Water-borne diseases
In Carlisle, the Mcvitie’s biscuit factory was flooded, leading to the temporary loss of how many jobs?
Over 1000
Positive environmental impacts of flooding
- Recharging groundwater systems
- Filling wetlands
- Increasing connectivity between aquatic habitats
- Move sediment and nutrients around the landscape and into marine environments
- Breeding, migration and dispersal
Negative environmental impacts of flooding
- Excessive overland flow can cause intense flooding, leading to eutrophication, and the oversupplies of sediment and nutrients - this destroys aquatic plants and organisms; nitrates, chemicals and heavy metals can degrade aquatic habitats
- Impacts wildlife living in the soil: earthworms, moles, voles, hedgehogs, badgers
Impacts of the Aswan Dam on the Nile Basin
- It aimed to control flooding in the Nile
- It had a negative impact of subsistence farmers, and also on sardine fishermen, as the sardines migrated away from the Nile Delta because of the loss of nutrient supply
Flooding in England and Wales date?
Summer 2007
Met Office figures for the months the flooding occurred over showed how much rain fell in England and Wales?
387mm over 3 months, which was double the average of 186mm
How were the river Thames and Severn affected?
- By 20th July 2007, rainfall along the course of the River Severn had reached record levels, leading to financial costs of £6 million and causing many social problems
- Shrewsbury - flooding had increase 6-fold of what the town had previously seen, but was mitigated by their flood defences built in 2003
- Worcester - river levels rose 4.5m above normal, flooding occurred 6 times in Upton-upon-Severn in 2007
- Tewkesbury and Gloucester - greatest impacts occurred here
Why is modelling climate change trends complex?
- Climate dynamics - no understanding to the way the atmosphere, ocean, terrestrial, cryosphere and biosphere systems all interact with each other
- Due to teleconnections, it can be difficult to distinguish the impacts of oscillations such as ENSO and climate change
- Global records are incomplete - insufficient depth or detail of evidence to establish reliable trends for the impact of climate change
Effect of climate change
Expected to influence precipitation, temperature and potential evapotranspiration - leads to severe drought events
Areas which have higher incidence and intensity of drought?
- Southern Europe
- South-Western USA
- The Sahel
Impacts of short-term climate change on water supply
- Increases in annual temperature - leads to greater evaporation from surface water and reservoirs in summer although spring discharge may increase
- Greater rates of evapotranspiration, desiccation of forests store
- Impact of oscillations, e.g. ENSO is leading to increasingly unreliable patterns of rainfall, e.g. less predictable monsoons
- More frequent cyclone and monsoon events threaten water supplies intermittently (irregular intervals)
- Increased intensity and frequency of droughts as a result of global warming and oscillation as issue for rainfed agriculturalists
- Depleted aquifers leads to problems with groundwater
- Decreasing rainfall in many areas as a result of global warming
- Loss of snow and glaciers as a store threatens many communities in mountain area, e.g. in Himalayas
The moisture-holding capacity of the atmosphere has been increasing at a rate of about what % per degree Celsius of climate warming?
7% - potential for heavier precipitation
What year was the wettest year ever recorded globally?
2010
How much have economic losses from heavy precipitation events increased between 1990 and 2010?
10x
Projections into the future occurrences of droughts and floods are very complex and hard to predict, both spatially and temporally, for a number of reasons:
- Multiple causes of climate change
- Insufficient understanding of teleconnections within earth systems
- Lack of availability of long-term big data sets
