Global trends in hazards and disasters

Trends in hydro-meteorological hazards

Evidence comes from records of floods, droughts and cyclones (Skill (5): use line graphs to describe trends over time; describe the overall trend, give start and end values, and point out fluctuations and anomalies).

Explanations:

• Physical: changing weather patterns and climate change; a warmer atmosphere and ocean can supply more energy and moisture to storms and heavy rain.
• Human: deforestation increases runoff and landslides; desertification and overgrazing worsen drought impacts; urbanisation adds impermeable surfaces.

Disaster trends 1970 to 2019 (WMO, 2021)

• More than 11,000 weather, climate and water disasters, just over 2 million deaths and US$3.64 trillion of losses.
• The number of disasters increased fivefold over 50 years.
• Deaths fell almost threefold, from about 50,000 a year in the 1970s to fewer than 20,000 a year in the 2010s.
• Losses rose sevenfold, from about US$49 million a day in the 1970s to US$383 million a day in the 2010s.
• More than 91% of deaths were in developing countries. Droughts (650,000 deaths) and storms (577,232) were the deadliest types.

Explaining the trends

• More recorded disasters: better reporting and communications; more people and assets in exposed places (coasts, floodplains, cities); possibly more extreme events.
• Rising economic losses: more valuable property and infrastructure exposed, especially in developed and emerging economies; insurance records losses better.
• Falling deaths: early warnings, forecasting, evacuation, shelters and better disaster management.
• More people affected: population growth and urbanisation in hazard zones.

Skill (6): bar charts and chi-squared

Use bar charts or histograms to compare disaster types or regions. The chi-squared test checks whether an observed distribution differs significantly from what would be expected by chance:

chi-squared = sum of (O - E) squared / E

• O = observed frequency, E = expected frequency (often total / number of categories).
• Degrees of freedom = number of categories - 1.
• If chi-squared is larger than the critical value (for example 7.81 for 3 degrees of freedom at the 0.05 level), reject the null hypothesis of no difference.

Worked example

Practice data (invented): flood disasters in four regions were 30, 18, 12 and 20. Test whether they differ from an even distribution.

1. Total = 80, so E = 20 in each region.
2. (30-20)2/20 + (18-20)2/20 + (12-20)2/20 + (20-20)2/20
3. = 5 + 0.2 + 3.2 + 0
4. Degrees of freedom = 3; critical value at 0.05 = 7.81.

Answer: chi-squared = 8.4, larger than 7.81, so the difference is significant at the 0.05 level.

Check yourself

1. WMO: economic losses rose from US$49 million a day (1970s) to US$383 million a day (2010s). By what factor did they rise? Give your answer to 1 decimal place.
   Show answer

   7.8. 383 / 49 = 7.8 (WMO describes this as sevenfold).

2. WMO: annual deaths fell from about 50,000 (1970s) to fewer than 20,000 (2010s). Using 20,000, calculate the minimum percentage fall.
   Show answer

   60 %. (50,000 - 20,000) / 50,000 x 100 = 60%.

3. Practice data (invented): observed cyclone landfalls in three regions are 25, 10 and 15. Using an even expected distribution, calculate chi-squared.
   Show answer

   7.0. E = 50/3 = 16.67; chi-squared = 7.0.

4. Which best explains why disaster deaths have fallen while the number of recorded disasters has risen?
   • Fewer people now live in hazard zones
   • Hazards have become weaker everywhere
   • Better forecasting, early warnings and evacuation
   • Disasters are no longer recorded in developing countries
   Show answer

   Better forecasting, early warnings and evacuation. Warnings and preparedness save lives even as exposure rises.

5. Why have economic losses from disasters risen so much since 1970?
   • More valuable property and infrastructure are located in exposed areas
   • Deaths have increased
   • Insurance has disappeared
   • Hazards now only strike rural areas
   Show answer

   More valuable property and infrastructure are located in exposed areas. Wealth and assets in exposed places have grown.

6. According to the WMO, what share of deaths from weather, climate and water disasters (1970 to 2019) occurred in developing countries?
   • About 50%
   • About 25%
   • More than 91%
   • Less than 10%
   Show answer

   More than 91%. Vulnerability and lower capacity are concentrated in developing countries.

7. Suggest why part of the increase in recorded disasters since 1970 may not be a real increase in hazards.
   Show answer

   Reporting and communications have improved, so more events are recorded; also more people now live in exposed areas, so events that were once hazards now count as disasters.. Better reporting and greater exposure increase the count without more hazards.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• WMO press release: Weather-related disasters increase over past 50 years (1 September 2021)

Last updated 8 November 2026. Spotted a mistake? Tell us.