Water EQ2

• According to UN, drought is an extended period - a season, a year or several years of deficient rainfall relative to statistical multi-year average for a region.
• Meteorological drought: occurs where long-term precipitation is lower than average and changes for different regions as it is affected by atmospheric conditions.
• Agricultural drought: happens when there isn't enough soil moisture to allow enough crops to grow and is caused by precipitation shortages, changes in evapotranspiration rates and decreased groundwater levels.
• Hydrological drought: Happens when amount of surface and subsurface water (rivers, lakes, reservoirs and groundwater) is deficient. Caused by lack of precipitation and usually occurs after meteorological and agricultural drought.
• Socio-economic drought: Occurs when water demand exceeds water availability - could be caused by lack of precipitation or by human overuse of sources of water.
• El Nino-Southern Oscillation (ENSO) occurs in Pacific Ocean and has a global impact on weather patterns, resulting in more intense storms in some places and drought in others
• Walker cell - circulation of air whereby upper atmospheric air moves eastwards, and surface air moves west across the Pacific, causing trade winds.
• What is La Nina characterized by?


  Intensification of normal conditions in the Pacific.
• How does La Nina affect pressure systems in the Pacific?


  Low pressure over the western Pacific becomes lower and high pressure over the eastern Pacific increases.
• What is the impact of La Nina on rainfall patterns?


  Rainfall increases over Southeast Asia while South America suffers drought.
• What causes the strengthening of trade winds during La Nina?


  Increased pressure differences between the western and eastern Pacific.
• When can La Nina occur in relation to El Nino?


  La Nina can occur just before or after El Nino.
• What is El Nino characterized by?

  Reversals of normal directions of ocean currents and winds in the Pacific Basin.
• How often do El Nino events typically occur?


  Every 7 years.
• How long do El Nino events usually last?


  About 18 months.
• What temperature increase can occur in the eastern Pacific during El Nino?


  Temperatures can rise by up to 8 degrees Celsius.
• What atmospheric condition forms due to low pressure during El Nino?


  Low pressure draws in westerly winds from the Pacific.
• What happens to warm, moist air during El Nino?

  It rises and creates heavy rainfall over the eastern Pacific.
• What is the effect of descending air during El Nino?


  It creates drier conditions leading to drought in Northern Australia and Indonesia.
• Southern Oscillation Index (SOI) - change in air pressure between 'normal' years ad El Nino is called ENSO. Strength, direction and speed is called SOI. Meteorologists record air pressure at Easter Island (west of South America) and subtract it from that at Darwin in northern Australia to calculate the SOI. Sharp drop indicates El Nino is imminent. Most droughts affect eastern and northern Australia thus resulting from ENSO and El Nino.
• What years did the tropical droughts in Brazil occur?

  2014-2015
• What is the primary direction of air movement across the Amazon Basin?


  Most air moves in a western direction
• What happens when moist air encounters the Andes mountain range?


  It is forced to run southwards
• How do high-pressure systems affect rain-bearing winds in the Amazon Basin?


  They divert rain-bearing winds further from the north, away from the Amazon
• What was the impact of high-pressure systems on the Andes mountains during the drought?


  They prevented rain-bearing winds from diverting southwards from the Andes
• Where did heavy rain occur during the drought period?

  In Bolivia and Paraguay
• How did human activity contribute to the drought in Brazil?

  Through over abstraction of surface-water resources and groundwater aquifers
• What actions did water companies take during the drought?


  They tried to maintain water supply for factories and services
• What did residents do to cope with the water supply issues during the drought?


  They tried to avoid cuts in supply
• Impacts of tropical droughts in Brazil 2014-2015

  • Water rationing for 4 million people; water supplies cut off for 3 days a week in some towns
  • Halting of HEP production leads to further power cuts
  • Depletion of Brazil's 17 largest reservoirs to dangerously low levels - some below 1% capacity
  • Increased groundwater abstraction so aquifer levels become dangerously low
  • Reduced crop of coffee beans resulted in global coffee prices increasing by 50%
• Rainforests recycle half of their rainfall, but positive feedback loop of deforestation and less rainfall is reducing ability of rainforest to regenerate. Results in rainforest ecosystems becoming less resilient.
• Reduced forest cover reduces soil water storage and evapotranspiration hence altering and affecting weather patterns
• Forests regulate regional climate and generate flows of moisture across continent. The combined risk of global climate change, ENSO cycles and deforestation alters this and results in more extreme weather events.

  • Amazon rainforests capacity to absorb carbon declines
  • Regional water cycles change and soil temperatures will increase
  • Amazon rainforest replaced with savannah-like grasslands
  • More wildfires increase level of carbon in atmosphere
  • Reduced rainfall will threaten Brazil's dependency on HEP (generates 70% of electricity)
  • Word lose major carbon sink and source of moisture
• Positive feedback - cyclical sequence of events that amplifies or increases change
• Negative feedback - cyclical sequence of events that amplifies or increases change
• Negative feedback - cyclical sequence of events that damps down or neutralises effects of a system
• Tipping point - when system changes from one state to another
• Resilience - ability of system to bounce back and survive
• Ecosystem stress - refers to constraints on development or survival of ecosystems. Constraints can be physical (drought), chemical (pollution) and biological (diseases)
• Ecosystem resilience - capacity of an ecosystem to recover from disturbance or to withstand an ongoing pressure such as drought