Lecture 7: Climate change impacts and their human footprint on the Global South

Question 1

Climate change attribution

Answer 1

What is it?

Studies how human-induced climate change influences weather patterns and extremes
Why important?

Separates natural variability from human influence
Used in policy, adaptation, and loss & damage debates
Two types:

Trend attribution – long-term changes
Event attribution – chance of a specific extreme due to climate change
→ e.g. heatwave in Europe, rainfall in East Africa

Question 2

Attribution: global findings

Answer 2

Human influence already affects all inhabited regions
Contributes to heat, drought, heavy rainfall
Attribution studies mainly in Global North → large gaps in Global South
Reasons for gap (Otto et al., 2020):

Few long-term observations
Poor model performance for tropics
Expertise & funding gap
Climate models tuned to Global North

Solutions:

Use reanalysis data, rescue old data
Capacity building in Global South
Include vulnerability and exposure

Health example

Human-induced climate change caused more heat-related deaths (1991–2018)
Highest in parts of Latin America, South Asia, Middle East
Defining events clearly is important

Definition affects attribution outcome
Hazards should match impacts (e.g. for heatwaves: use temperature and duration/scale)

Question 3

Case Study – Lake Victoria (East Africa)

Answer 3

2020 flood event
Very heavy rainfall (late 2019–early 2020) → record lake levels
700,000–2 million people affected by flooding
Attribution analysis
Studied lake level increase from Nov 2019 to May 2020
1.21 m rise = 63-year event in current climate
Simulated using water balance model (precipitation, evaporation, inflow, outflow)
Attribution result:

Event is 1.8× more likely now than in pre-industrial climate
Lake rose ~7 cm more than without climate change (6% of rise)
→ One of first attribution studies in East Africa

Question 4

Lake Victoria - future projections

Answer 4

Rainfall ↓, evaporation ↑ (RCP8.5)
Lake level change depends on outflow management:
Constant hydropower = large variation (±12m)
Current outflow policy = smaller variation (±3.9m)
Climate models have large uncertainty
Night-time storms projected to worsen
→ More intense storms at night by end of century

Question 5

Intergenerational water inequality

Answer 5

Young people will face more water scarcity than older generations
How?
Uses “lifetime exposure” concept
Shows how many people will live with unmet water demand
Example:

3.7 billion people aged 0–60 in 2020 will not have half their lifetime water demand met
→ 55% of this population

Question 6

Water scarcity

Answer 6

1. Falkenmark indicator – <500 m³/cap/yr = absolute scarcity
2. Water scarcity index (WSI) – water use / water availability > 0.4 = scarcity

Water deficit = total water needed but not available, integrated over a lifetime

Disadvantages:
- Only exposure
- Choice of thresholds (literature)
- Saturation effects (once water scarce, will remain)

Question 7

Lifetime water deficit

Answer 7

Lifetime water deficit higher for youth and Global South
Gap grows across generations (especially in Africa, Middle East, South Asia)
Top 15 countries with worst water scarcity: Egypt, Yemen, Sudan, Eritrea, etc.
Driven by:
Irrigation
Domestic
Industrial use
Biggest rise in irrigation demand

Question 8

Policy message

Answer 8

Emission scenarios have limited effect on lifetime water scarcity
→ Main driver = population increase
Urgent need for adaptation, especially in countries with low capacity
A new vulnerable group is emerging: people with ≥70% unmet water need