Edexcel GCSE Geography A (1GA0) — The Human Environment
Our planet is known as the "Blue Marble", but only a tiny fraction of its water is actually available for human use. The relationship between the amount of water a region receives and the amount it loses or uses is known as the water balance.
A region's water balance can be calculated using a simple equation:
When a region experiences a prolonged deficit, it faces water stress (where annual supply falls below per person). This can worsen into (below ) or (below ). Examiners expect you to distinguish between (a lack of water due to climate or geology) and (where water exists, but a region lacks the infrastructure or wealth to collect and treat it).
Why do some countries have vast river networks while others rely on expensive desalination? The primary physical factor is precipitation. Arid regions, which make up 40% of the Earth's land, receive only 2% of global precipitation, leading to severe physical water deficits.
Evapotranspiration and relief also play major roles. High temperatures in tropical or desert regions cause immense water loss through evaporation. Conversely, mountainous regions experience high orographic rainfall; combined with steep slopes and low population density, this usually creates a water surplus.
Geology determines how water is stored underground. Permeable rocks, like chalk and limestone, allow water to infiltrate and form an aquifer (e.g., the London Basin chalk aquifer). Impermeable rocks prevent infiltration, increasing surface runoff and reducing natural water storage.
Climate change (the Enhanced Greenhouse Effect) is severely impacting physical supply. Higher global temperatures increase evaporation rates from reservoirs. Furthermore, sea levels have risen 23 cm since 1880, causing salinization where saltwater intrudes into and ruins coastal freshwater aquifers.
You can turn off the tap to save water, but the biggest drains on our water supply happen before it even reaches your home. Over-abstraction is a major human cause of deficit; for example, the water table of the Ogallala Aquifer in the USA has dropped by over 35 metres in 50 years due to intense pumping.
Poor infrastructure heavily contributes to deficits. Globally, approximately 126 billion cubic metres of treated water are lost every year due to leaking pipes. In the UK, 25% of treated water is lost daily, while in developing regions, leakage rates frequently exceed 30% due to overburdened systems.
Pollution effectively reduces the usable water supply, creating economic scarcity. In China's Shanxi province, 80% of water is unsuitable for agriculture due to industrial waste, while 90% of sewage in developing countries is discharged untreated.
These physical and human factors often combine to create distinct regional patterns. In the UK, the North and West have high rainfall and low populations (surplus), whereas the South and East have lower rainfall but very high population densities, resulting in a severe human-driven water deficit.
The global population has grown rapidly since 1950, but our thirst for water has grown even faster. Global water consumption tripled between 1950 and 2018, rising from 1.22 trillion cubic metres to over 4 trillion cubic metres.
To calculate the percentage increase in global water demand over this period, you use the percentage change formula:
How much did global water consumption increase between 1950 and 2018?
Step 1: Identify the values.
Step 2: Substitute into the equation.
Step 3: Calculate the final percentage.
This explosion in demand is driven by rising wealth and changing lifestyles. The UK has shifted from a 1950s "weekly shared bath" culture to a modern "showering society", increasing household water use by 70% since 1985. The average UK citizen now uses 149-150 litres per day, compared to just 4 litres in Mozambique.
Rapid industrialisation in Newly Emerging Economies (NEEs) like India and China has massively increased demand for water in manufacturing and cooling. Additionally, global dietary shifts toward meat require huge volumes of water; producing 1 kg of beef requires roughly 15,000 litres of water compared to just 1,300 litres for 1 kg of wheat.
This agricultural demand has fueled a boom in the virtual water trade (water hidden in exported goods), which more than doubled between 1986 and 2010. Countries now "import" water by buying food grown elsewhere, masking their own internal deficits.
While demand skyrockets globally, the actual amount of usable, accessible freshwater on Earth is steadily shrinking. Over the last 50 years, relentless over-abstraction and climate change have decimated surface water stores.
Lake Chad in Africa has shrunk to just 5% of its 1960s size due to a combination of lower rainfall and heavy extraction for irrigation. Similarly, prolonged droughts and over-use left Lake Mead in the USA at just 25% capacity by 2022.
Water quality degradation has also slashed available supply. As NEEs industrialise rapidly, environmental regulations often lag behind. Today, 13 of the 20 most polluted cities globally are in India, where rivers like the Ganges receive millions of litres of toxic industrial effluent daily. This pollution does not destroy the water molecules, but it removes the water from the safe, usable supply, escalating the global water crisis.
Students often confuse physical and economic water scarcity. Ensure you state that economic scarcity means the water is actually there, but a lack of infrastructure or money (e.g., due to pollution treatment costs) means it cannot be used safely.
When asked to 'Analyze' causes of water deficit, examiners expect you to explicitly link physical factors (like low precipitation) to human factors (like over-population or leaks) rather than discussing them in isolation.
In 6-mark or 8-mark 'explain' questions about changing demand, you must use specific statistics (e.g., global consumption rising from 1.22 to over 4 trillion cubic metres) to support your points and secure the top band of marks.
When discussing the UK's water imbalance, clearly distinguish between the physical cause (high relief rainfall in the West) and the human cause (high population density in the East).
Water balance
The relationship between the amount of water a region receives (supply) and the amount it loses or uses (demand).
Water surplus
A situation where the available water supply exceeds the demand from the population, industry, and agriculture.
Water deficit
A situation where the demand for water is greater than the available supply.
Water stress
When the annual supply of water in a region falls below 1,700 cubic metres per person.
Water scarcity
A severe shortage where the annual supply of water falls below 1,000 cubic metres per person.
Absolute scarcity
When the annual supply of water falls below 500 cubic metres per person.
Physical water scarcity
A lack of available water due to natural climate conditions (like low rainfall) or geographical factors.
Economic water scarcity
When water is physically present, but a region lacks the wealth or infrastructure to collect, treat, and distribute it safely.
Evapotranspiration
The combined process of water loss to the atmosphere through evaporation from the Earth's surface and transpiration from plants.
Orographic rainfall
Precipitation that occurs when moist air is forced to rise over mountains or hills, cooling and condensing as it rises.
Aquifer
An underground layer of water-bearing permeable rock, such as chalk or limestone, which can be extracted for human use.
Salinization
The process by which freshwater sources become contaminated with salt, often due to rising sea levels pushing saltwater into coastal aquifers.
Over-abstraction
The process of extracting water from natural sources, such as underground aquifers or surface stores, at a rate faster than it can be replenished.
Newly Emerging Economies (NEEs)
Countries undergoing rapid industrialisation and economic growth, which rapidly increases their industrial water demand.
Virtual water trade
The hidden flow of water between countries through the trade of food and manufactured goods that required water to produce.
Put your knowledge into practice — try past paper questions for Geography A
Water balance
The relationship between the amount of water a region receives (supply) and the amount it loses or uses (demand).
Water surplus
A situation where the available water supply exceeds the demand from the population, industry, and agriculture.
Water deficit
A situation where the demand for water is greater than the available supply.
Water stress
When the annual supply of water in a region falls below 1,700 cubic metres per person.
Water scarcity
A severe shortage where the annual supply of water falls below 1,000 cubic metres per person.
Absolute scarcity
When the annual supply of water falls below 500 cubic metres per person.
Physical water scarcity
A lack of available water due to natural climate conditions (like low rainfall) or geographical factors.
Economic water scarcity
When water is physically present, but a region lacks the wealth or infrastructure to collect, treat, and distribute it safely.
Evapotranspiration
The combined process of water loss to the atmosphere through evaporation from the Earth's surface and transpiration from plants.
Orographic rainfall
Precipitation that occurs when moist air is forced to rise over mountains or hills, cooling and condensing as it rises.
Aquifer
An underground layer of water-bearing permeable rock, such as chalk or limestone, which can be extracted for human use.
Salinization
The process by which freshwater sources become contaminated with salt, often due to rising sea levels pushing saltwater into coastal aquifers.
Over-abstraction
The process of extracting water from natural sources, such as underground aquifers or surface stores, at a rate faster than it can be replenished.
Newly Emerging Economies (NEEs)
Countries undergoing rapid industrialisation and economic growth, which rapidly increases their industrial water demand.
Virtual water trade
The hidden flow of water between countries through the trade of food and manufactured goods that required water to produce.
