4.2
Factors in nature affect the water cycle In this topic, you will learn that:
• the water cycle can be affected by the movement of water vapour in the air • changes in temperature, the direction of the wind and the number of plants can change the amount of water vapour.
The effect of El Niño on Australia You may have heard of the El Niño effect. Fisher people in Peru, South America, originally used this term to describe the appearance, around Christmas, of a warm ocean current off the coast that brought heavy rain and floods. Nowadays, ‘El Niño’ describes the extensive warming of the central and eastern Pacific Ocean. Combined with this ocean warming are changes in the atmosphere that affect weather patterns across countries around the Pacific Ocean, including Australia. In Australia, El Niño events usually mean less rain will fall. El Niño events occur approximately every 4–7 years and usually last for about 12–18 months. They are a natural part of the climate
AF T
Figure 1 Areas in Australia affected by a drought and b flood
system and have been affecting the Pacific countries for thousands of years. Each El Niño event is unique in terms of how much the ocean temperature warms and how rainfall patterns change. El Niño events usually result in less rain across parts of eastern and northern Australia, particularly during winter, spring and early summer. Where and when this happens differs a lot from one event to another, even with similar changes and patterns in the Pacific Ocean. In 2015–16, a relatively weak El Niño event resulted in severe drought.
a
More recently, in 2020–21, a La Niña event caused widespread flooding. The opposite of El Niño, La Niña occurs when the ocean current
D
R
b
The effect of La Niña on Australia
Increased convection
Trade winds
Equator
Figure 2 During an El Niño event, there is an increased chance of drier conditions in Australia because of the combined effects of ocean warming and changes in the atmosphere that affect weather patterns.
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S outh America Austr alia Less rain
Warmer than normal
˜
El Nino
Cooler than normal
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