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Spec mapping (AQA 7037): Paper 1, §3.1.5 Hazards — the specification names wildfires in areas of fuel build-up and seasonal rainfall as a required hazard study: "nature of wildfires; conditions favouring intense wildfires (vegetation type, fuel characteristics, climate and recent weather, fire behaviour); causes — natural and human; impacts (primary/secondary, social, economic, environmental); short- and long-term responses." Drought is the slow-onset hazard that creates much of the fuel-and-weather conditions for wildfire, so the two are taught together. It links synoptically to the atmospheric-systems lesson (ENSO, IOD, the subtropical highs that aridify regions), to §3.1.1 (drought as a perturbation of the water cycle; fire as a carbon-cycle event), and to §3.2.x (the wildland–urban interface as human exposure). Assessment objectives: AO1 (drought types, fire triangle, fire behaviour), AO2 (applying to located events — Black Summer, California), AO3 (drought indices, area-burned/cost data, climate-attribution figures).
Droughts and wildfires are slow-onset hazards that can persist for months or years, affecting agriculture, water supply, ecosystems and human health. They are often interconnected: prolonged drought dries vegetation, creating the conditions for catastrophic wildfires. As climate change intensifies, these hazards are becoming more frequent and severe in many parts of the world. Understanding their causes, impacts and management is essential for the AQA Hazards specification. A key conceptual thread is that wildfire is unusual among the hazards in this option because it is partly a natural and even necessary ecological process — many ecosystems are fire-adapted — so the "hazard" arises largely from where humans have placed themselves (the WUI) and how fire regimes have been altered, making it the clearest case of a socially-constructed disaster overlaying a natural process.
Key Definition: A drought is a prolonged period of abnormally low precipitation relative to the statistical average for a region, leading to a shortage of water for people, agriculture and ecosystems. Unlike other hazards, drought has a gradual onset and no precise beginning or end.
| Type | Definition | Indicator |
|---|---|---|
| Meteorological drought | A sustained period in which precipitation is significantly below the long-term average for the region | Measured by precipitation deficit (e.g., < 75% of average for 3+ months) |
| Agricultural drought | Insufficient soil moisture to meet the needs of crops at a particular growth stage | Measured by soil moisture levels and crop yield data |
| Hydrological drought | Reduced streamflow, reservoir levels and groundwater levels, usually lagging behind meteorological drought by weeks or months | Measured by river discharge, reservoir levels, groundwater monitoring |
| Socio-economic drought | The point at which drought begins to affect the supply and demand of economic goods — food, water, energy | Measured by food prices, water rationing, economic losses |
The four types form a cascade: a precipitation deficit (meteorological) first depletes soil moisture and stresses crops (agricultural), then — weeks to months later, as the deficit propagates through the catchment — lowers rivers, reservoirs and groundwater (hydrological), and finally, if it persists, disrupts the supply of food, water and energy and triggers rationing and economic loss (socio-economic). This time-lag is crucial for management: meteorological drought can be detected early from rainfall records, giving warning before the hydrological and socio-economic impacts arrive — which is why drought indices (such as the Standardised Precipitation Index, SPI, or the US Drought Monitor's composite categories) are valuable early-warning tools. It also explains why drought, uniquely among hazards, has no clear start or end point: it is defined relative to a long-term statistical normal and is only recognised in hindsight, which makes declaring (and de-declaring) a drought a political as well as a scientific act.
graph LR
A["Meteorological<br/>Drought<br/>(weeks)"] --> B["Agricultural<br/>Drought<br/>(weeks-months)"]
B --> C["Hydrological<br/>Drought<br/>(months)"]
C --> D["Socio-economic<br/>Drought<br/>(months-years)"]
| Cause | Mechanism |
|---|---|
| Changes in atmospheric circulation | Shifts in the jet stream or subtropical high-pressure belts can redirect moisture-bearing weather systems away from a region. Persistent blocking anticyclones prevent rainfall |
| El Nino-Southern Oscillation (ENSO) | El Nino events suppress rainfall in Australia, Indonesia, southern Africa and northeast Brazil while increasing rainfall in western South America. La Nina events can cause drought in southwestern USA and the Horn of Africa |
The ENSO mechanism is worth understanding because it is the single largest driver of year-to-year drought variability in the tropics and subtropics. In a normal (neutral) year, strong easterly trade winds pile warm surface water in the western Pacific, where rising air feeds heavy rainfall over Indonesia and northern Australia, while cold water upwells off South America. In an El Niño year the trades weaken or reverse, the warm pool and its rainfall shift eastward into the central/eastern Pacific — so Indonesia, eastern Australia and parts of southern Africa are left under descending, drying air and suffer drought (and consequently fire), while normally arid coastal Peru receives floods. La Niña is the intensified opposite phase. Because ENSO operates on a ~2–7-year cycle and can be forecast months ahead, it offers genuine seasonal predictability of drought and fire risk — a forecasting tool for the management end of the topic. The catastrophic 2019–20 Australian fire season coincided with a strongly positive Indian Ocean Dipole (the IOD is ENSO's Indian-Ocean cousin), which suppressed moisture inflow to Australia. | Indian Ocean Dipole (IOD) | A positive IOD (warmer western Indian Ocean, cooler east) reduces rainfall in Australia and Southeast Asia | | North Atlantic Oscillation (NAO) | Influences winter rainfall patterns across Europe; a negative NAO phase can reduce rainfall in southern Europe | | Monsoon variability | Weakened or delayed monsoon seasons cause drought across South and Southeast Asia — affecting billions of people |
| Factor | How It Worsens Drought |
|---|---|
| Deforestation | Reduces evapotranspiration, decreasing atmospheric moisture and rainfall (a positive feedback). The Amazon generates ~50% of its own rainfall through transpiration — deforestation risks pushing the system past a tipping point (Lovejoy and Nobre, 2018) |
| Over-abstraction of water | Groundwater depletion lowers water tables; rivers are over-extracted for irrigation. The Aral Sea has lost 90% of its area since 1960 due to Soviet-era irrigation projects diverting its feeder rivers |
| Soil degradation | Compacted or degraded soils have reduced infiltration capacity, increasing runoff and reducing soil moisture storage |
| Climate change | Higher temperatures increase evapotranspiration, exacerbating drought even without reduced rainfall. Some regions are experiencing reduced precipitation as well |
| Urbanisation | Impermeable surfaces prevent infiltration; increased water demand from growing populations |
Key Definition: Desertification is the degradation of land in arid, semi-arid and dry sub-humid areas, resulting from climatic variations and human activities (UNCCD, 1994). It does not mean the expansion of existing deserts but rather the degradation of productive land.
The Sahel — the semi-arid transition zone south of the Sahara Desert stretching 5,000 km from Senegal to Eritrea — is the most cited example of desertification:
| Factor | Detail |
|---|---|
| Climate | Annual rainfall 200–600 mm; highly variable from year to year; devastating droughts in 1968–1974 and 1983–1985 killed an estimated 250,000 people and millions of livestock |
| Population growth | Population has increased from ~30 million (1950) to ~140 million (2020), placing enormous pressure on land and water resources |
| Overgrazing | Livestock numbers have increased; overgrazing removes vegetation, exposing soil to wind erosion |
| Overcultivation | Shortened fallow periods deplete soil nutrients; marginal land is brought into cultivation |
| Deforestation | Firewood is the primary fuel source; trees are cleared for agriculture; roots that bind soil are lost |
| Wind erosion | Exposed, degraded soil is blown away by the Harmattan wind, creating dust storms that can reach Europe |
The Sahel is the textbook example of a slow-onset hazard produced by the interaction of physical variability and human pressure. The physical driver is the region's inherently variable rainfall — it sits at the fluctuating northern limit of the West African monsoon and the ITCZ's seasonal swing, so a southward shift of the rain belt brings multi-year drought (as in 1968–74 and 1983–85). But the disaster is amplified by human pressure on a fragile system: a population that has more than quadrupled since 1950 forces shortened fallow periods, overgrazing and the clearance of soil-binding trees for fuel, stripping the land's resilience just as the climate stresses it. This makes the Sahel a powerful synoptic case for the "disasters are not natural" argument applied to a slow-onset hazard — and a hopeful one, because the success of low-cost, community-based regreening (zai pits, agroforestry, the Great Green Wall) shows that the human side of the equation can be reversed.
Key Definition: A wildfire is an uncontrolled fire in an area of combustible vegetation. Wildfires are a natural part of many ecosystems but become hazards when they threaten lives, property and livelihoods.
Crucially, fire is ecologically functional in many biomes: some species are pyrophytic (fire-adapted), requiring fire to germinate (e.g. certain eucalypts and Mediterranean shrubs have seeds released or triggered only by heat), to clear competition, or to recycle nutrients. This is why total fire exclusion is itself harmful — it removes a natural process and allows fuel to build. The hazard, then, is not fire per se but fire of abnormal intensity or in the wrong place, which is overwhelmingly a product of human ignition, fuel mismanagement and the placement of settlement in fire-prone landscapes.
Three elements must be present for fire:
graph TD
A["FUEL<br/>Vegetation, organic matter"] --- B["HEAT<br/>Ignition source<br/>(lightning, human)"]
B --- C["OXYGEN<br/>Wind supplies O2"]
C --- A
A --> D["FIRE"]
B --> D
C --> D
| Cause | Details |
|---|---|
| Natural | Lightning strikes (responsible for ~15% of wildfires in the USA); volcanic activity; spontaneous combustion of dry organic matter |
| Human | Arson; unattended campfires; discarded cigarettes; agricultural burning that escapes control; power line sparks; gender reveal parties (the 2020 El Dorado Fire in California was ignited by a pyrotechnic device at a gender reveal party) |
| Climate-related | Higher temperatures dry out vegetation (reducing fuel moisture content); earlier snowmelt extends the fire season; drought creates extreme fire conditions |
| Factor | Effect |
|---|---|
| Fuel type | Grasses ignite easily but burn quickly; shrubs and chaparral burn intensely; mature forests produce crown fires |
| Fuel moisture | Dry fuel ignites more easily; drought conditions create extreme fire risk |
| Wind speed and direction | Wind supplies oxygen, drives the fire forward, and carries embers ahead of the fire front (spot fires) |
| Topography | Fire travels faster uphill (pre-heating of fuel); slopes, canyons and gullies channel and accelerate fire |
| Temperature | Higher temperatures reduce fuel moisture and increase fire intensity |
| Relative humidity | Low humidity dries vegetation and makes fire spread easier |
Examiners reward precise vocabulary for how a fire burns. Ground fires smoulder slowly through peat and soil organic matter and can persist for months; surface fires burn through grass, leaf litter and low vegetation; crown fires leap from treetop to treetop and are the most intense, fast and uncontrollable. The most dangerous behaviour is spotting, where wind lofts burning embers ("firebrands") far ahead of the main front, igniting new fires that can leap firebreaks and trap people who believe they are safe behind the front. In the most extreme events a fire can generate its own weather: a pyrocumulonimbus cloud forms above the plume, and the resulting downdrafts and even fire-generated lightning make the fire's behaviour erratic and effectively unfightable (multiple pyroCb events occurred during Black Summer). Recognising the vegetation–weather–topography combination that produces crown fires and spotting is the core of the spec's "conditions favouring intense wildfires."
| Aspect | Details |
|---|---|
| Duration | September 2019 – March 2020 (unusually long fire season) |
| Area burned | 18.6 million hectares (186,000 km2 — larger than England and Wales combined) |
| Deaths | 33 direct deaths; an estimated 445 additional deaths from smoke inhalation across Australia's eastern seaboard |
| Buildings destroyed | 5,900 buildings including 2,779 homes |
| Wildlife | An estimated 3 billion animals killed or displaced (WWF, 2020) — including significant populations of koalas, wombats, and flying foxes |
| Cause | Record-breaking drought (2017–2019, the driest recorded period for much of eastern Australia); record-breaking temperatures (December 2019 was Australia's hottest month ever); the positive Indian Ocean Dipole reduced moisture inflow; lightning ignitions during dry thunderstorms |
| Air quality | Smoke blanketed Sydney, Melbourne and Canberra for weeks; air quality reached hazardous levels (PM2.5 concentrations > 500 micrograms/m3 — 20 times the WHO guideline); hospitals saw 50% increases in respiratory admissions |
| Climate change | The fires were consistent with projected increases in fire weather severity. Australia's CSIRO concluded that climate change had made the conditions leading to the 2019–2020 fires at least 30% more likely |
| Economic cost | $100+ billion AUD including ecological losses, health costs, property destruction and agricultural losses |
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