Drought

• Drought


  A water deficit in a particular place over a period of time, compared to an average rainfall for that same period
• Global climate change is increasing the development of drought through increased evaporation, brought on by rising temperatures and the severely affected area has doubled to more than 30% in the past 30 years
• Main types of droughts

  • Meteorological
  • Agricultural
  • Hydrological
• Meteorological drought


  Dry weather patterns dominating an area
• Agricultural drought


  Lack of moisture in the surface soil, causing it unable to support plant life
• Hydrological drought


  Evidence of low water supply - in reservoirs, streams etc.
• Drought can occur as a result of physical causes as well as human
• Causes of droughts can be short and long term
• Atmospheric motion


  Vertical movement of air (rising or subsiding) or horizontal (wind)
• Wind


  Horizontal movement of air, resulting from a difference in air pressure, which in turn may be caused by differences in temperature and the force exerted by gravity
• El-Nino Southern oscillation (ENSO)


  Used to describe the combination of oceanic and atmospheric impact of the phenomenon which leads to a disruption in the climate system centred around the pacific basin
• Normal Pacific conditions (Walker circulation)

  1. Trade winds from East (Peru) to West (Australia)

  2. Warm water pushed West

  3. Upwelling, evaporation takes place near australia

  4. Heavy rainfall over Pacific

  5. South America had colder waters
• El-Nino Event


  1. Trade winds weaken, or reverse

  2. Ocean currents slow causing rainfall over South America, does not reach the middle of Pacific

  3. Sea level also changes as a result (eustatic change)

  4. South America gets regular rain storms and flooding

  5. Australia will have droughts
• La-Nina Event


  1. Stronger normal conditions

  2. Trade winds are stronger

  3. Ocean current and upwelling stronger

  4. Causing rain storms and flooding over Australia

  5. South America suffers from droughts
• ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe
• The 2015-2016 El Niño event was one of the strongest El Niño events on record. It reached its peak in late 2015 and continued into early 2016. Australia experienced widespread drought conditions
• Climate change is intensifying drought across the state. Water Year 2022 started wet with a strong atmospheric river and ended in continued drought due to almost no precipitation during January through March
• Heatwaves during El Niño events can pose health risks, particularly to vulnerable populations such as the elderly and those with pre-existing health conditions
• California's small, rural communities of colour are most vulnerable to drought
• At least 2,600 well-dependent households experienced water shortages in California
• Decreased agricultural output and increased bushfire damage caused job losses and reduced income for farmers in Australia
• The combination of reduced rainfall and higher temperatures fueled an intense bushfire season in southeastern Australia. The prolonged drought and bushfires had a significant impact on Australia's wildlife, leading to habitat destruction and threats to various species
• Droughts harm wildlife that live in California's rivers, streams, and wetlands
• In September 2022 100% of California was declared as being abnormally dry, 40% in extreme drought, and 16.6% in exceptional drought
• Unusually warm temperatures in 2021, nearly 3.5 ºF (1.9 ºC) above the 20th-century average, created an additional 3-4 inches of evaporative demand, and an 8% increase in crop water demands in California
• Millions of people in California are already subject to unprecedented water restrictions and many in rural areas are expecting their wells to run dry within months, if not weeks
• California's agricultural sector generates more than $50 billion (€48 billion) in revenue yearly while also employing more than 420,000 people
• Drier than normal conditions caused by El Nino led to drought and wildfires in Australia in 2015
• Two homes, two sheds and two vehicles were destroyed by the wildfire in Australia in 2016
• Australia experienced its fourth-warmest year on record during 2016, with national temperatures 0.87℃ above average
• Drought impacts on Forests

  Drought increases the likelihood of fungal diseases in forest pines and threatens their survival, providing conditions for diseases to spread through the forest trees
• Tipping point


  When a 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 effect of the system
• Resilience


  The ability of a system to "bounce back" and "survive"
• Forest: Responsibly for much of the earth’s interception, reducing flooding and overland flow/surface runoff. 
• Wetlands: 10% of the earth surface. They act as water stores, recharge aquifers and trap pollutants
• Drought impacts on wetlands:Drought courses less interception, infiltration etc. The water table falls, there is less water stored, which decreases the action performed by the wetland. 
• California droughts: coursed unemployment to rise, especially in the agricultural business