Water stress and water scarcity (physical and economic)

Water Stress and Water Scarcity (Physical & Economic)

Learning Objective

Explain the concepts of water stress, physical water scarcity and economic water scarcity; analyse global trends in water demand and supply; evaluate water‑resource management strategies – in line with Cambridge International AS & A Level Geography (9696) Topic 5 – Water Resources & Management.

Key Definitions

• Water Stress: The ratio of total water demand to total renewable water resources in a given area. Expressed as a dimension‑less Water Stress Index (WSI).
• Physical Water Scarcity: Renewable water resources are insufficient to meet total demand (demand > supply). In the Cambridge syllabus this is signalled by a WSI ≥ 0.6.
• Economic Water Scarcity: Water is physically available but cannot be accessed because of inadequate infrastructure, financial constraints, or weak institutions.
• Water Security: The capacity of a population, region or basin to ensure the sustainable availability of water of acceptable quality, in sufficient quantity, to meet social, economic and environmental needs now and in the future. It comprises four dimensions – availability, accessibility, quality, sustainability.

Global Water‑Resource Types (5.1)

Cambridge identifies five major water‑resource categories and their approximate share of the planet’s total freshwater:

• Glaciers & Ice‑sheets – ~68 % of global freshwater (mainly in Antarctica & Greenland).
• Groundwater – ~30 % (the most important source for drinking water worldwide).
• Surface water (rivers, lakes & reservoirs) – ~2 % (highly variable in space and time).
• Atmospheric water (precipitation) – the flux that re‑charges the above stores.
• Artificial storage (dams, reservoirs, inter‑basin transfers) – a managed component of surface water.

Figure: World schematic showing the relative size of each water‑resource type (placeholder‑world‑water‑pie.jpg).

Human Water Cycle (5.1.1)

• Extraction → Use (domestic, agricultural, industrial) → Return (treated/untreated) → Re‑entry into the natural cycle (evaporation, infiltration, runoff).
• Key concept: Renewable water availability is the portion of the cycle that can be sustainably abstracted each year without degrading the resource.

Measuring Water Stress – Water Stress Index (WSI)

$$\text{WSI}= \frac{D}{A}$$

• D = total annual water demand (km³ yr⁻¹)
• A = total annual renewable water availability (km³ yr⁻¹)

Global Patterns of Water Consumption (2020‑2022)

Drivers of Increasing Water Consumption (5.1.2)

1. Population growth: World population rose from 6.1 billion (2000) to 8.0 billion (2023); domestic demand rises ~1 % yr⁻¹.
2. Urbanisation: >55 % of people now live in cities; per‑capita urban use is 1.5–2 × rural use.
3. Economic development: A 10 % rise in GDP per‑capita typically raises industrial water use by ~3 % (World Bank, 2022).
4. Dietary changes: Higher meat and dairy consumption increases “virtual water” demand; 1 kg beef ≈ 15 000 L water.
5. Climate change: Altered precipitation and higher evaporation have reduced renewable supply in many basins by 5‑15 % since 2000.

Physical vs Economic Scarcity – Case Studies

Physical Scarcity – Jordan River Basin (Middle East)

Renewable supply: < 1 km³ yr⁻¹
Total demand (agri + domestic + industrial): ≈ 2 km³ yr⁻¹
WSI: ≈ 2.0 → Severe stress (physical scarcity)

• Over‑extraction has left the river dry for > 30 years.
• Consequences: loss of wetlands, reduced groundwater recharge, heightened geopolitical tension among Israel, Jordan and Palestine.
• Evaluation: Physical scarcity limits options; only supply‑side augmentation (e.g., desalination) or major demand‑reduction (water‑saving irrigation) can relieve stress, both of which are costly and politically sensitive.

Economic Scarcity – Rural Ethiopia

Renewable supply: ≈ 1 500 km³ yr⁻¹ (ample)
Actual access: < 30 % of households have reliable piped water.

• Constraints: low investment in wells/pipelines, limited technical capacity, high operation‑and‑maintenance costs.
• Health impact: reliance on unsafe surface water causes > 15 % of diarrhoeal disease cases.
• Evaluation: Improving infrastructure would rapidly raise water security, but requires sustained financing, community participation and strong institutions.

Water‑Resource Infrastructure (Syllabus 5.3.1‑5.3.2)

• Dams & Reservoirs: Store seasonal runoff, regulate flow, generate hydro‑electric power. Example – Three Gorges Dam (China) supplies ~30 % of the Yangtze’s water demand.
• Inter‑basin Transfers: Move water from water‑rich to water‑poor regions (e.g., China’s South‑to‑North Water Transfer Project – 44 km³ yr⁻¹ transferred).
• Desalination: Converts seawater to freshwater; meets ~1 % of global demand, but >50 % of domestic water in Gulf states.
• Rain‑water Harvesting & Small‑scale Storage: Widely used in arid zones; improves resilience to seasonal variability.
• Waste‑water Treatment & Reuse: Provides secondary water for agriculture and industry; reduces pressure on freshwater sources.

Trans‑boundary Water Issues & Conflict/Co‑operation (Water Security)

• Conflict example: Jordan River Basin – disputes over allocation of limited flows.
• Co‑operation example: Indus Water Treaty (1960) between India and Pakistan – survived multiple wars, allocates river flows and provides a joint‑management framework.
• Key syllabus point – water security includes the ability to manage trans‑boundary resources peacefully and sustainably.

Implications of Water Stress

• Reduced agricultural yields → heightened food insecurity.
• Sectoral competition → potential for intra‑national or international conflict.
• Higher water tariffs → disproportionate burden on low‑income households.
• Ecological degradation: loss of wetlands, reduced riverine biodiversity, altered sediment transport.

Mitigation and Management Strategies (Evaluation)

1. Demand‑side Management
   • Water‑saving appliances, drip irrigation, leak detection.
   • Pricing reforms (tiered tariffs) encourage conservation.
   • Evaluation: Low‑cost and quick to implement, but effectiveness depends on public acceptance and enforcement.
2. Supply‑side Augmentation
   • Desalination – reliable but energy‑intensive and costly; best for high‑income coastal regions.
   • Rainwater harvesting – cheap, community‑based; limited by climate variability.
   • Waste‑water reuse – reduces freshwater demand; requires treatment infrastructure and public trust.
   • Evaluation: Provides additional water but can create environmental impacts (e.g., brine disposal) and may exacerbate inequality if not equitably distributed.
3. Improved Governance (IWRM)
   • Integrated Water Resources Management coordinates planning across sectors and borders.
   • Stakeholder participation improves legitimacy and compliance.
   • Evaluation: Institutional reforms are essential for long‑term sustainability but often face political resistance and need capacity‑building.
4. Agricultural Efficiency
   • Drip and sprinkler systems cut water use by 30‑50 %.
   • Crop switching to less water‑intensive varieties (e.g., millets instead of rice).
   • Evaluation: High water‑saving potential; adoption hindered by upfront costs and farmer knowledge gaps.
5. Climate‑adaptation Measures
   • Optimised reservoir operation to capture extreme flood events.
   • Restoration of floodplains and wetlands to enhance natural storage.
   • Evaluation: Enhances resilience but may conflict with existing land‑use (e.g., agriculture) and requires long‑term monitoring.

Summary – Key Points to Remember

• WSI = D/A; a value ≥ 0.6 signals severe stress (physical scarcity).
• Physical scarcity = insufficient renewable supply; economic scarcity = lack of access despite adequate supply.
• Water security integrates availability, accessibility, quality and sustainability, and includes trans‑boundary governance.
• Agriculture dominates global water use, especially in developing regions; urbanisation shifts demand toward domestic and industrial sectors.
• Drivers of demand: population (+1 % yr⁻¹), urbanisation, rising incomes, diet, and climate‑induced supply changes.
• Effective management combines demand reduction, supply augmentation, robust institutions and conflict‑avoidance mechanisms.

Suggested Exam Questions (AO1‑AO3)

1. Define physical water scarcity and economic water scarcity. Using the Jordan River Basin, explain how a region can experience both types of scarcity.
2. Calculate the Water Stress Index for a basin with a demand of 0.9 km³ yr⁻¹ and a renewable supply of 1.2 km³ yr⁻¹. State the stress level according to the syllabus thresholds.
3. Using the table of sectoral water use, analyse why Sub‑Saharan Africa shows a higher WSI than Europe. Include at least two drivers of water demand in your answer.
4. Evaluate the effectiveness of two mitigation strategies (one demand‑side, one supply‑side) for reducing water stress in a rapidly urbanising megacity such as Delhi.
5. Discuss how trans‑boundary water agreements can enhance water security, using the Indus Water Treaty as an example.

Quick‑scan of the Lecture‑Note Packet against the 9696 Syllabus (Topic 5 – Water Resources & Management)