The role of human activity in altering biophysical processes through land clearing, urbanisation, agriculture, mining, and resource use

What this dot point is asking

NESA wants you to recognise that humans now alter every biophysical process at every scale. The HSC asks "examine", "analyse" or "explain" questions on the human role in environmental change. Strong answers name multiple human activities, link each to a biophysical process, and supply Australian impact data.

The main vectors of human modification

Land clearing

Australia has cleared around 50 percent of its original woodland and forest since 1788. Queensland alone cleared 7.7 million hectares between 2000 and 2020, mostly for cattle grazing. The Bureau of Statistics records continued woody vegetation clearing at around 400,000 ha per year nationally.

Process impact. Reduced evapotranspiration alters local moisture and rainfall. Removed root systems destabilise soils, increasing erosion and sediment loads. Lost canopy interception increases stormflow peaks. Removed carbon sinks contribute around 12-18 percent of Australia's total greenhouse emissions.

Urbanisation

Around 86 percent of Australians live in urban areas. Sydney, Melbourne, and Brisbane between them cover roughly 30,000 km2 of formerly natural or agricultural land. Greater Sydney is projected to grow by another 1.7 million people to 2041.

Process impact. Impervious surfaces (roads, roofs, parking) increase runoff and reduce groundwater recharge. Sydney's combined sewer-stormwater overflows during heavy rain still discharge raw sewage into harbour waters. Urban heat island effects raise city centre temperatures 1-3 degrees C above the rural surround. Air pollution from vehicle emissions and wood-fire heating causes around 1,700 premature deaths per year in Sydney (UNSW air quality study, 2022).

Agriculture

Around 60 percent of the Australian landmass is used for agriculture, mostly extensive grazing. Cropping covers around 6 percent of the continent. Irrigated agriculture extracts around 9,000 GL of water per year, around 65 percent of total Australian water use.

Process impact. Cropping replaces deep-rooted native vegetation with shallow-rooted annuals, raising water tables and creating dryland salinity (over 2 million ha affected). Fertiliser runoff contributes nitrogen and phosphorus to rivers, driving algal blooms and seagrass die-off. Livestock methane is around 10 percent of national emissions.

Mining and resource extraction

Australia produced 480 Mt of black coal, 900 Mt of iron ore, 30 Mt of bauxite, and significant gold, copper, zinc, and uranium in 2023. Open-cut mines disturb large surface areas; underground mining causes subsidence that alters drainage patterns.

Process impact. Mine pit lakes and acid mine drainage acidify surface and groundwater. Tailings dams contain heavy metals and process chemicals; failures (Mount Lyell, Ranger) have contaminated waterways for decades. Coal exports drive global atmospheric CO2.

Pollution

Industrial and consumer pollution adds chemicals, plastics, nutrients, and noise to natural systems. Australian beach surveys find around 7,000 pieces of plastic per square kilometre of beach. PFAS chemicals from defence and industrial sites have contaminated groundwater across multiple sites (Williamtown NSW, Oakey QLD).

Climate change

The cumulative effect of all human activity is anthropogenic climate change, which now alters every other biophysical process. Australian average temperatures have risen 1.5 degrees C since 1910. Sea level has risen around 22 cm globally since 1900. Ocean pH has fallen 0.1 units, with measurable acidification on the Great Barrier Reef.

The compounding effect

The strongest answers recognise that human activities interact. Land clearing increases runoff, which combines with urban impervious surfaces to increase flooding. Agriculture and mining both add nutrients and contaminants to the water cycle. Climate change amplifies the consequences of land clearing (drier soils, hotter fires) and urbanisation (higher heat island effects on heat-vulnerable populations).

The Australian Bureau of Meteorology's State of the Climate (2022) integrates these vectors: every spectrum of biophysical change in Australia is now influenced by human activity.

Management framing

Management responses operate at three scales:

• International. Paris Agreement commitments (Australia's target: 43 percent emissions reduction by 2030 from 2005 levels), Convention on Biological Diversity, RAMSAR wetlands.
• National. Climate Change Act (2022), Environment Protection and Biodiversity Conservation Act (1999), Native Vegetation Act regimes per state.
• Local. Land-use planning, native vegetation retention, riparian buffer rules, urban green infrastructure.

Effectiveness varies. Queensland land clearing rates fell after 2018 Vegetation Management Act amendments but rose again from 2020. Climate Change Act targets remain aspirational without sectoral policy. Local councils have most effective implementation tools.