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Heat wave followed by flooding in a subsiding coastal city

A conditional statement under stated assumptions, never a prediction.

2 min read0 figures0 tables4 notesNR-SECTOR-CITIES-GLOBAL-2026-BASELINE

Contents
  1. ·Edition home
  2. ·Executive summary
  3. 1Cities are where the systems meet
  4. 2Key findings
  5. 3Systems and sectors at baseline
  6. 4Risks and capability
  7. 5Heat wave followed by flooding in a subsiding coastal city
    1. 5.1 Assumptions
    2. 5.2 The cascade, step by step
    3. 5.3 The scenario as a table of steps
  8. 6Readings from the other desks
  9. 7The 2027 agenda
  10. 8Systems in depth
  11. AMethodology
  12. BData appendix
  13. CReferences and record
  14. ·Complete edition, for print

5.1Assumptions

Scenario SCN-GS10-HTF-01: what is assumed, and what is held constant.

Baseline
the 2026 reference state in this edition
Drivers
a multi-day heat wave in a dense coastal city, followed within weeks by intense rainfall or storm surge on land that is subsiding
Analogues
Europe 2022 heat10; urban heat exposure record14; coastal subsidence evidence1626
Interventions
none modelled: the specification describes the unmitigated case
Run state
narrative specification; quantified run scheduled for 2027

5.2The cascade, step by step

  1. 1

    CLI → HLT

    heat raises illness and deaths among older and poorer residents

    2022

  2. 2

    CLI → ENE

    cooling load peaks and local power is stressed

    2022

  3. 3

    CLI → WAT

    heavy rain or surge meets drains and low ground weakened by subsidence

    2022 to 2026

  4. 4

    WAT → INF

    flood reaches roads, clinics, drainage and power

    2022

  5. 5

    WAT → HLT

    water-borne illness and injury rise in informal settlements

    2022

  6. 6

    INF → FIN

    repair bills and lost output strain municipal budgets

    2022

5.3The scenario as a table of steps

How the shock in scenario SCN-GS10-HTF-01 would travel through Global Cities and Urban Systems‘s coupled systems, step by step, under the assumptions the edition states.

StepWhat happensSource
01 Climate to healthHeat raises illness and deaths among older and poorer residents. Analogue or source: 2022.Edition GS-10, scenario SCN-GS10-HTF-01, step 1
02 Climate to energyCooling load peaks and local power is stressed. Analogue or source: 2022.Edition GS-10, scenario SCN-GS10-HTF-01, step 2
03 Climate to waterHeavy rain or surge meets drains and low ground weakened by subsidence. Analogue or source: 2022 to 2026.Edition GS-10, scenario SCN-GS10-HTF-01, step 3
04 Water to infrastructureFlood reaches roads, clinics, drainage and power. Analogue or source: 2022.Edition GS-10, scenario SCN-GS10-HTF-01, step 4
05 Water to healthWater-borne illness and injury rise in informal settlements. Analogue or source: 2022.Edition GS-10, scenario SCN-GS10-HTF-01, step 5
06 Infrastructure to financeRepair bills and lost output strain municipal budgets. Analogue or source: 2022.Edition GS-10, scenario SCN-GS10-HTF-01, step 6

A teaching model of a conditional scenario under the edition’s stated assumptions: not a forecast, not a prediction and not a warning. Sources: Global Cities 2026, scenario SCN-GS10-HTF-01 (2026); Global Cities 2026, references (NR-CIT-1) (2026).

Notes

Numbers are the edition’s reference numbers, so a note reads the same in every chapter. The full list, with every source and its licence, is in Annex C. Annex C, references

  1. 10WHO (ed.), Climate change, heat and health, fact sheet (about 489,000 heat-related deaths a year, 2000 to 2019; Europe summer 2022). World Health Organization, Geneva. Observation year 2019. Accessed 2026-11-03.back
  2. 14Tuholske, C. et al., Global urban population exposure to extreme heat, Proceedings of the National Academy of Sciences 118(41), e2024792118 (open access full text, PMC). National Academy of Sciences, Washington, 2021. Observation year 2016 (series 1983 to 2016). Accessed 2026-11-03.back
  3. 16Global subsidence of river deltas, Nature (2026), open access full text, PMC. Springer Nature, London. Observation year 2026 (40 deltas, satellite radar). Accessed 2026-11-03.back
  4. 26Sinking cities, rising seas, Communications Engineering (2022), commentary on a Nature Sustainability study of relative land subsidence in 48 major coastal cities (open access full text, PMC). Springer Nature, London. Observation year 2022. Accessed 2026-11-03.back

Cite this chapter

Valadbaygi, S. (Ed.). (2026). Chapter 5: Heat wave followed by flooding in a subsiding coastal city. In Global Cities Risk and Resilience Report 2026: Baseline Edition, The State of the World’s Cities and Urban Systems. (Baseline Edition 2026, Report No. NR-SECTOR-CITIES-GLOBAL-2026-BASELINE) [Draft under review]. The Global Centre for Risk and Innovation (GCRI).

Every citation form of the whole report, BibTeX and RIS included, is on the edition home. Cite this report

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Sector signature

The sectors behind Global Cities and Urban Systems.

A reading aid: the sectors the findings run through and how strongly they depend on each other.

Select corners · hover lines6 / 15 relations

Context

Heatwave

Cooling demand peaks the grid while rivers warm; heat stress fills hospitals and wilts crops.

W · E · I · F · H · B

Sectors
4 of 6
Relations
6 of 15
Coupling
0.43 share of total

Strongest relations in play

  • Water → Energy · cooling water and hydropower0.6
  • Water → Food · irrigation0.8
  • Food → Health · nutrition0.7
  • Water → Health · drinking water and sanitation0.7
Teaching values for a typical city-region, not measurements for any place. Coupling is the summed strength of the relations in play, as a share of all fifteen.
The Global Centre for Risk and Innovation

Science · evidence · measurement

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