Natural and ecological hazards are potential sources of harm whose distribution, magnitude and frequency vary spatially and over time.

What this dot point is asking

A hazard is not the same as a disaster. A hazard is the potential source of harm, the process or event itself, while a disaster is what happens when that hazard affects a vulnerable community and overwhelms its capacity to cope. An earthquake in an uninhabited desert is a hazard but not a disaster. This distinction matters because it shows that harm depends on both the physical event and the human exposure to it, a theme that runs through the whole hazards unit.

Geographers classify hazards by origin. Geophysical (or geological) hazards come from the Earth itself: earthquakes, volcanic eruptions, tsunamis and landslides. Atmospheric (or meteorological) hazards come from the atmosphere: tropical cyclones, severe storms, hailstorms, heatwaves and drought. Hydrological hazards involve water: river and flash flooding, and storm surge. Biological or ecological hazards involve living organisms: disease epidemics, plagues, invasive species and bushfire, which sits at the boundary of atmospheric and ecological hazards. Many hazards are compound, where one triggers another, such as an earthquake causing a tsunami, or drought intensifying bushfire.

Hazards are described using several measurable characteristics. Spatial distribution is where hazards occur and why, which is rarely random. Earthquakes and volcanoes cluster along tectonic plate boundaries such as the Pacific Ring of Fire. Tropical cyclones form over warm tropical oceans and so affect northern Australia, not Tasmania. Magnitude is the size or energy of an event, measured on scales such as the moment magnitude scale for earthquakes or categories for cyclones. Frequency is how often events of a given size occur, often expressed as a recurrence interval, such as a one-in-one-hundred-year flood. Duration ranges from seconds for an earthquake to months for a drought. Scale of spatial impact ranges from a localised landslide to a continental drought.

Tasmania illustrates how distribution and type vary with place. The 2016 floods across the north and east followed intense rainfall and caused damage and loss of life, a hydrological hazard. The state has a long history of bushfire, an ecological and atmospheric hazard, including the 1967 Black Tuesday fires around Hobart and more recent dry-lightning fires that burned fire-sensitive vegetation in the Tasmanian Wilderness World Heritage Area. The spread of the long-spined sea urchin into eastern Tasmanian waters is an ecological hazard driven by ocean warming, harming kelp and fisheries. Globally, contrasting examples include the 2011 Tohoku earthquake and tsunami in Japan, a high-magnitude geophysical compound hazard, and recurrent tropical cyclones in the Pacific.

Climate change is altering hazard patterns, increasing the frequency and intensity of some atmospheric and ecological hazards. Longer, hotter, drier fire seasons raise bushfire risk; warmer seas shift the range of marine pests; and heavier rainfall events increase flood risk. This means historical frequency records may understate future hazard, an important point for management and planning.

For TCE assessment, be able to classify a hazard by origin, describe its spatial distribution and explain why it occurs where it does, and use the vocabulary of magnitude, frequency, duration and scale with specific figures and named events. Pair a Tasmanian or Australian example with a global one, and set up the analysis of risk and management that follows in later dot points.