The challenge of natural hazards

A natural hazard is a natural event that threatens people or property. The word that does the work is threatens: an earthquake in an empty desert is a natural event, but it is not a hazard until there is something for it to harm.

That distinction runs through the whole topic. It is why two earthquakes of the same magnitude can kill nobody in one country and thousands in another.

Types of natural hazard fall into two groups:

• tectonic hazards, caused by movement of the Earth's crust — earthquakes and volcanic eruptions • atmospheric, or meteorological, hazards, caused by weather and climate — tropical storms, droughts and extreme weather.

Factors affecting hazard risk are the reason risk is not the same everywhere:

Earthquakes and volcanic eruptions are the result of physical processes.

Plate tectonics theory states that the Earth's crust is broken into plates that float on the mantle beneath and move slowly, driven by convection in the mantle and by the pull of the plate as it sinks at a subduction zone.

The global distribution of earthquakes and volcanic eruptions is not random. Both occur in narrow bands, and those bands mark the plate margins — which is itself the strongest evidence for the theory. The Pacific Ring of Fire is the clearest example. Earthquakes also occur at conservative margins, where there are no volcanoes at all, so the two distributions overlap but are not identical.

The effects of, and responses to, a tectonic hazard vary between areas of contrasting levels of wealth.

• Primary effects happen immediately, as a direct result of the event — buildings collapse, people are killed or injured, roads crack. • Secondary effects follow on afterwards — fires from broken gas pipes, disease from contaminated water, homelessness, lost income, landslides blocking aid routes. • Immediate responses happen in the hours and days afterwards — search and rescue, treating the injured, emergency shelter, water and food. • Long-term responses take months or years — rebuilding, repairing infrastructure, improving building regulations, restoring the economy.

You need named examples to show how the effects and responses vary between two areas of contrasting levels of wealth. Your school will have chosen a pair — typically one earthquake in a higher income country and one in a lower income country.

What matters is that you can use them to make the comparison, not that you use any particular pair. The general pattern to explain, and then evidence from your own examples:

• In a lower income country, buildings are often poorly constructed and not built to withstand shaking, so more collapse and more people die. There is less money for search and rescue equipment, hospitals are quickly overwhelmed, and the country may need international aid. Rebuilding is slow because money is short. • In a higher income country, buildings are more likely to be designed to resist earthquakes and there are trained emergency services with equipment ready, so fewer people die even in a large event. Economic losses in pounds are often higher, because the buildings and businesses damaged are worth more.

That last point is worth holding on to: the poorer country usually loses more lives, and the richer country usually loses more money.

Management can reduce the effects of a tectonic hazard.

Reasons why people continue to live in areas at risk:

• the soil on volcanic slopes and river plains is very fertile, so farming is good • they were born there, their family and work are there, and they cannot afford to move • volcanoes attract tourists and geothermal energy, bringing jobs and income • minerals are found near volcanoes • the risk feels small — a major event may not have happened in living memory • they believe monitoring and building design will protect them.

The specification names the *type* of case study, never the place — your school chose which. The worked example below is one in common use; if your school taught a different one, use theirs and keep the same structure, because the structure is what the marks are for.

Global atmospheric circulation helps to determine patterns of weather and climate.

The general atmospheric circulation model describes how air moves between the equator and the poles in three cells in each hemisphere, creating belts of high and low pressure at the surface and the winds that blow between them.

One rule explains the whole model: air rises at low pressure, giving cloud and rain, and sinks at high pressure, giving clear skies and drought.

Tropical storms — hurricanes, cyclones and typhoons — develop as a result of particular physical conditions. They are the same phenomenon under three regional names.

Their global distribution follows directly from those conditions: they form over warm oceans between about 5° and 30° north and south of the equator, and they move westwards then curve away from the equator.

The relationship with general atmospheric circulation is what ties this to the model above. Tropical storms form in the low pressure belt near the equator, where air is already rising strongly. They do not form exactly on the equator, because the Earth's rotation is what makes the rising air spin, and that effect is zero at the equator itself.

The causes and sequence of formation:

1. The sun warms a large area of ocean to at least about 27 °C. 2. Warm, moist air rises rapidly, creating an area of very low pressure. 3. As the air rises it cools, and the water vapour condenses into towering thunderclouds — releasing huge amounts of heat energy, which powers the storm. 4. More warm air is drawn in at the surface to replace it, and the Earth's rotation makes the whole system spin. 5. The storm moves westwards, gathering more energy from the warm ocean and growing stronger. 6. On reaching land it loses its energy source and weakens rapidly, though it may still do great damage.

How climate change might affect tropical storms: warmer oceans could allow storms to form over a wider area, so their distribution may spread further from the equator; higher sea temperatures give storms more energy, so their intensity is expected to increase. The evidence for a change in frequency is much less clear, and saying so is a stronger answer than claiming all three will rise.

Tropical storms have significant effects on people and the environment, and the same four headings apply as for tectonic hazards: primary effects, secondary effects, immediate responses and long-term responses.

You need a named example of a tropical storm to show its effects and responses. Use the one your school studied. Whichever it is, the answer needs specific detail — how strong the winds were, how many people were affected, what was actually done — because "buildings were damaged" could be said of any storm and earns little.

How monitoring, prediction, protection and planning reduce the effects of tropical storms:

• Monitoring: satellites track storms from the moment they form, and aircraft fly into them to measure pressure and wind speed. • Prediction: computer models forecast the likely track several days ahead, so warnings can be issued. • Protection: buildings on stilts above the storm surge, reinforced roofs and windows, sea walls, and storm shelters. • Planning: evacuation routes and drills, emergency supplies stockpiled, and restricting building in the highest-risk coastal areas.

Unlike earthquakes, tropical storms can be predicted days in advance — which is why deaths from them have fallen sharply in countries with good warning systems, even though the damage to property has not.

The UK is affected by a number of weather hazards. An overview of the types: rain and flooding, strong winds and storms, snow and ice, drought and extreme heat, and occasionally thunderstorms with lightning and hail.

Extreme weather events in the UK have impacts on human activity. You need an example of a recent extreme weather event in the UK to illustrate its causes, its social, economic and environmental impacts, and how management strategies can reduce risk. Again, use the event your school studied, and make sure you can name it, date it and quote figures for it.

Evidence that weather is becoming more extreme in the UK: records for temperature, rainfall and wind have been broken more often in recent decades; several of the warmest years on record have occurred recently; and there have been a number of severe flood events in a short period. Note the careful wording — the evidence points to an increase, but any single storm or heatwave cannot on its own prove a trend, and a good answer says so.

Climate change is the result of natural and human factors, and has a range of effects.

Evidence for climate change from the beginning of the Quaternary period to the present day. The Quaternary is the geological period covering roughly the last 2.6 million years, during which the climate has swung repeatedly between glacial and interglacial conditions.

Possible causes of climate change:

Natural factors • Orbital changes — the shape of the Earth's orbit, and the tilt and wobble of its axis, change over tens of thousands of years, altering how much solar energy reaches the Earth. These are the accepted explanation for the cycle of ice ages. • Volcanic activity — large eruptions throw ash and gas high into the atmosphere, reflecting sunlight and cooling the Earth for a year or two. • Solar output — the energy the Sun emits varies slightly in cycles of about eleven years.

Human factors • Use of fossil fuels — burning coal, oil and gas releases carbon dioxide, the largest single human contribution. • Agriculture — livestock produce methane, and rice paddies release it too; methane is a far more powerful greenhouse gas than carbon dioxide. • Deforestation — fewer trees means less carbon dioxide removed by photosynthesis, and burning the cleared timber releases more.

An overview of the effects of climate change on people and the environment:

On the environment — sea level rise flooding low-lying land, more coastal erosion, ice sheets and glaciers melting, coral bleaching, and species forced to move or facing extinction as their habitats change.

On people — crop yields falling in some regions and rising in others, water supplies becoming less reliable, more people at risk from flooding, health effects from heatwaves and the spread of diseases into new areas, and people displaced from land that becomes uninhabitable.

Managing climate change involves both mitigation, which means reducing the causes, and adaptation, which means responding to the change. The distinction is examined directly and is easy to keep straight: mitigation tackles the cause, adaptation copes with the consequence.