• The Sustainable Development Goals have helped more people get clean water and sanitation, but much more work is needed for others. • Cross-boundary water management must be planned so upstream and downstream populations share water fairly. • Personal behaviours can help minimise water use and wastage. • Governments help manage drought and water scarcity. This includes building desalination plants and encouraging responsible water use at home. 9.8 What are the causes and impacts of hydrometeorological hazards? • The Earth’s atmosphere protects us from the extremes of the sun’s heat, creating conditions that support life. • Our weather is the result of constant changes to the air in the troposphere, temperature, air movement and moisture content. These changes sometimes cause extreme weather events. • Weather is the day-to-day, short-term change in the atmosphere at a particular location. • Climate is the average of weather conditions that are measured over a long time. • Natural hazards are common in Australia, including drought, floods and bushfires. • A hazard is an event that is a potential source of harm to a community, whereas a disaster is an event that has an actual impact on a community. • The four broad types of natural hazard are atmospheric, hydrological, geological and biological. 9.9 What are the causes and impacts of droughts and flooding rain? • A drought is a long time with less rain, causing not enough water for daily needs. • Sustained periods of drought can have varied and significant impacts on environments and communities. • Good planning can reduce drought impacts, but poorer countries struggle more than wealthy ones. • A floodplain is flat land by a river that floods when the river water slows down. • These fertile, flat areas are used for farming and settlement around the world. • Managing floods is important, but not all countries have the resources to do so. • Floods are managed by building barriers like levees, dams and floodgates to stop excess water. 9.10 Why does the wind blow? • Earth’s atmosphere protects us from the extremes of the sun’s heat and the chill of space, making conditions right to support life. • Wind is caused by air moving from areas of high pressure to areas of low pressure. • The direction in which winds circle depends on whether you are in the northern or southern hemisphere. As the air moves from an area of high pressure to an area of low pressure, winds circle in the opposite direction in each hemisphere. 9.11 What are the causes and impacts of extreme weather? • Thunderstorms, also referred to as electrical storms, form in unstable, moist atmospheres where powerful updrafts occur, which happens when a cold front approaches. • Severe thunderstorms occur when a storm has one or more of the following features: flash flooding, hailstones, or wind gusts of 90 km/h or more. • Thunderstorms can occur at any time of the year, but are more likely to occur during spring and summer. • A snowstorm is officially recognised as a blizzard when wind speed is sustained above 56 km/h or has frequent gusts in excess of this speed for more than three hours. 9.12 What are the causes and impacts of cyclones? • Cyclones form when a cold air mass meets a warm, moist air mass lying over a tropical ocean with a surface temperature greater than 27 ° C. Cold air currents race in to replace rapidly rising, warm, moist air currents, creating an intense low-pressure system.
TOPIC9 Water in the world 335
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