SEE: Water: 5.4A

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  • 5.4A: The causes of drought
    • Drought is when there is a water deficit in a place over a period of time compared to the average rainfall for the same period
    • Meteorological drought
      • Deficiency in precipitation leads to reduced infiltration, runoff, deep percolation, and groundwater recharge
        • Short term precipitation deficit!
          • Long term deficit. Caused by things such as El nino events + climate change
            • Climate warming leads to increased evaporation
              • 2019 'Big Dry' in Australia thought to be as a result of long-term climate change
          • Change from a low to high pressure system which cannot form clouds and therefore causes drought
      • High temps, wind, low humidity, high sunshine, low cloud, lead to increase in evapotranspiration
      • Drought in 2000s Australia was made worse by changing air/ocean currents in the Pacific
    • Hydrological causes
      • Streamflow and groundwater levels decrease because of reduced precipitation and high rates of evaporation
      • Also results in reduced storage in lakes/reservoirs, decreasing water quality
      • Linked to decreasing water supplies for urban areas
    • Overtime, agricultural drought can ensue
      • Rainfall deficiency leads to soil moisture deficiency, reducing plant growth
        • This leads to a poor crop yield
    • ENSO cycles
      • El Nino can trigger drought, usually in its 2nd year, in South-East Asia, India, Eastern Australia
        • Reversal of trade winds/weakening of them leads to cooler ocean temps, high pressure, and drought conditions
      • La Nina can lead to drought conditions in South America
        • Cooler than normal ocean temps leads to strong high pressure and  to dry conditions and drought

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