Lecture 3: Water and Water Pressure

Question 1

Municipal water use

Answer 1

Water used for household and public service needs.

Though visible and important (drinking, hygiene), it comprises only a small share of total global withdrawals.

Strongly correlates with wealth: low-income households use 2–10 liters/day/capita; high-income exceed 250+ liters/day/capita.

Lack of safe water causes ~1.2 million deaths per year, mostly in the Global South (e.g., India, Pakistan, Sub-Saharan Africa).

Question 2

Industrial water use

Answer 2

Includes water for processing, cooling, and energy generation (excluding hydropower).

Large share of withdrawals in Global North; negligible in most of the Global South.

Question 3

Agricultural water use

Answer 3

Dominates global withdrawals (around 70%).

Up to 90% in low-income countries vs. ~43% in high-income countries.

Water demand stems from evapotranspiration: 3000 liters/day needed per person to produce food.

Producing 1 kg of yield requires ~1000–2000 liters of water.

Consumption varies by crop: lettuce (~250 l/kg) vs. beef (~21,000 l/kg).

Water required for crops can come from:
* Rainfall (effective rainfall).
* Irrigation (requires access to freshwater sources).

Question 4

Water availability

Answer 4

Total global water: ~1.39 billion km³.
* Only 2.5% is freshwater.
* Just 0.3% of total is easily accessible.

Annually renewable resources: ~42,000 km³.

Current use: ~7,500 km³/year.

Theoretically enough for 25 billion people under 1,700 m³/person/year.

But availability varies regionally:
* Africa: ~3,200 m³/person/year.
* Europe: ~6,500

Intra-country variation is also large.

Question 5

Water stress

Answer 5

Water stress = withdrawals / renewable resources.

Temporal stress due to seasonal rainfall and crop needs.
* Short growing seasons with high variability (esp. Sub-Saharan Africa). (ET<rainfall)
* Climate change increases uncertainty and stress.

Yield gap: irrigation needed to close it.
* Irrigated land = 17% of cropland but provides 33% of food.
* Limited by infrastructure and river/lake access.

Question 6

Physical vs economical water scarcity

Answer 6

Physical scarcity: demand > available resources.

Economic scarcity: water available, but inaccessible due to lack of infrastructure.

~50% of global population faces economic water scarcity.

Global South disproportionately affected.

Land degradation link:

• Land degradation reduces infiltration, increases runoff and erosion.
• Flash floods and sedimentation reduce reservoir capacity.
• Sediment affects water quality and irrigation infrastructure.
• Poor irrigation practices can worsen degradation (e.g. salinization).

Question 7

Better develop water infrastructure

Answer 7

Build new reservoirs.

Many dams planned/under construction, especially in Africa.

Concerns:
* Ecological: disrupt river ecosystems.
* Social: displacement, access disputes.
* Geopolitical: e.g. Nile Basin, Ethiopian Highlands (Tekeze, GERD).

Sediment threats shorten dam lifespan.

Question 8

Use Groundwater Reserves

Answer 8

Africa has large reserves (100x renewable freshwater), esp. in N. Africa.

Not sustainable long-term due to salinization and depletion.

Question 9

Soil and water conservation measures

Answer 9

Reduces erosion and increases infiltration.

Enhances green water availability.

Question 10

Increase Water Use Efficiency

Answer 10

WP = yield / water used (ET + losses).

Improve by:
* Drought-tolerant crops.
* Good agronomic conditions (soil fertility, density, weed control).
* Better irrigation (drip, sprinkler, mulch).
* Deficit irrigation (e.g. quinoa in Bolivia).