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Cities are where the systems meet

Part I describes systems and their couplings. It ranks no country or operator and assesses no authority.

7 min read2 figures1 table16 notesNR-SECTOR-CITIES-GLOBAL-2026-BASELINE

Contents
  1. ·Edition home
  2. ·Executive summary
  3. 1Cities are where the systems meet
    1. 1.1 The questions this part answers
    2. 1.2 The argument
    3. 1.3 Twenty couplings between five systems
  4. 2Key findings
  5. 3Systems and sectors at baseline
  6. 4Risks and capability
  7. 5Heat wave followed by flooding in a subsiding coastal city
  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

1.1The questions this part answers

Key questions

  • Where is cities risk concentrated?
  • Which couplings carry cities shocks into other systems?
  • Which cities capabilities hold under compound stress?
  • What must 2027 evidence measure first?

In this part

  • Narrative
  • Headline finding
  • Lead figure
  • Five coupling chapters
  • Twelve-domain reading
  • Sector screens
  • Dependency matrix
  • Risk objects
  • Capability ladder
  • Scenario
  • Three lenses
  • Portfolio

1.2The argument

Cities are usually described by size. The 2026 evidence reads them as the places where housing, services, finance and hazards meet. A person in a city depends on drinking supply, power, transport, food markets and a clinic within a few kilometres, and a single hazard can reach all of them237.

The definition matters. On the UN grid-based method 45% of people live in cities, and on national definitions 57.8% are urban12. The first method counts more than 12,000 cities and shows that most are small1. Policy designed for megacities reaches a minority of urban residents.

Risk is rising with exposure. Urban extreme heat exposure nearly tripled between 1983 and 2016, 1.81 billion people live in flood-exposed areas, and deltas and coastal cities are subsiding14131626. Informal settlements, home to about 1.12 billion people, are often excluded from adaptation plans512.

Cities are also where action can scale. Urban emissions were about 29 GtCO2-eq in 2020, yet per capita urban emissions are lower than national per capita emissions in most regions, and trees already offset part of the heat island615. Finance lags the need: cities receive less than 20% of the finance needed for climate action12.

Figure 1.1How large is the housing gap? Urban population in slums or informal settlements (million)

The share held near 25% while the urban population grew, so the number rose. The 2015 value is derived from the published increase of 130 million and is a derivation, not a reported figure5.

ItemBar, scaled to the largest valueValue
20221120
2015, implied by 130 million fewer990

Source: as cited in the note to this figure. Year 2022.

Figure ID FIG-SECTOR-CITIES-GLOBAL-2026-BASELINE-01-003

130million

more people in slums than in 20155

360million

added in Sub-Saharan Africa by 2030, expected5

31.0%

average housing cost burden, 124 countries, 20234

43.5%

housing cost burden in Sub-Saharan Africa, 20234

1.3Twenty couplings between five systems

The cities-centred matrix types the twenty couplings between the five core systems, read for their cities content. Strengths are Nexus estimates (ESTIMATED) from the cited evidence and analogue events; they set the graph that 2027 evidence will test.

Figure 1.2Couplings between the five systems

Each line is one coupling from one system to another, drawn by the strength the edition assigns. Strengths are Nexus estimates from the cited evidence and analogue events.

  • Strong
  • Moderate
  • Weak

Source: this edition’s coupling matrix (Table 1.1); status Estimated.

Table 1.1Coupling matrix: from the row system to the column system
From, toWATENEFOOHLTBIO
WAT Water·MODERATE
hydro · cooling water for urban power		MODERATE
irrigation for city food supply		STRONG
drinking supply · sanitation · flood		MODERATE
urban rivers and floodplains
ENE EnergySTRONG
pumping · treatment · drainage load		·MODERATE
cold chains · markets		STRONG
cooling · clinics · clean cooking		WEAK
land for supply · light
FOO FoodWEAK
peri-urban runoff		WEAK
food waste to energy		·STRONG
urban diets · food access		MODERATE
peri-urban land conversion
HLT HealthWEAK
workforce		WEAK
workforce		WEAK
labour		·WEAK
pollution load
BIO BiodiversityMODERATE
green and blue infrastructure buffers flood		MODERATE
canopy cuts cooling demand		WEAK
urban agriculture		MODERATE
green space · heat · child survival		·
Strength: strong, moderate or weak; a Nexus estimate (status Estimated) from cited evidence and analogue events. The scale is defined in Annex A.

Transmission paths

  1. 01

    CLI → INF → HLT

    A heat wave raises cooling demand while services fail; older and poorer residents are hit first.

    Reported urban heat exposure up 199% 1983 to 201614; 61,672 excess deaths in Europe in 202210

  2. 02

    CLI → WAT → INF

    Flood and storm surge reach drainage, power and transport at once in low-lying cities.

    Reported 1 billion in low-lying cities at risk by 20507; 1.81 billion flood-exposed13

  3. 03

    WAT → BIO → INF

    Subsiding land raises relative sea level beneath coastal cities.

    Reported delta subsidence study16; 48 coastal cities26

  4. 04

    FIN → INF → HLT

    Under-funded municipalities defer service upgrading, and informal settlements stay uncovered.

    Inferred cities receive under 20% of climate finance need12

  5. 05

    BIO → HLT

    Tree cover and canopy continuity are associated with lower heat harm and child mortality.

    Reported canopy and child mortality in 57 countries19; greenness and heat mortality18

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. 2DATA VINTAGE AFTER CLOSE: World Bank (ed.), World Development Indicators, API extract of urban population, total population, urban agglomerations, urban access to electricity, clean cooking, safely managed drinking water and sanitation, slum share (database updated 8 October 2026). World Bank, Washington. Observation year 2025 (population) and 2024 (access). Accessed 2026-11-03.back
  2. 3UN Statistics Division (ed.), Global SDG Indicators Database, API extract of series EN_LND_SLUM, EN_ATM_PM25, EN_ACS_URB_OPENSP, SP_TRN_PUBL, EN_REF_WASCOL and SD_CPA_UPRDP (release 2026.Q3.G.01). United Nations, New York. Observation year 2024 (slums), 2023 (PM2.5) and 2020 (transport, open space). Accessed 2026-11-03.back
  3. 7IPCC (ed.), Cities, settlements and key infrastructure, chapter 6 in Climate Change 2022: Impacts, Adaptation and Vulnerability, Contribution of Working Group II to the Sixth Assessment Report of the IPCC (downloaded chapter, executive summary read). IPCC, Geneva, 2022. Observation year 2020. Accessed 2026-11-03.back
  4. 1UN DESA Population Division (ed.), World Urbanization Prospects 2025: Summary of Results (publication page and press release; 45% of 8.2 billion people in cities, 33 megacities, more than 12,000 cities, Degree of Urbanisation). United Nations, New York, November 2025. Observation year 2025. Accessed 2026-11-03.back
  5. 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
  6. 13Rentschler, J., Salhab, M. and Jafino, B.A., Flood exposure and poverty in 188 countries, Nature Communications 13, 3527 (open access full text, PMC). Springer Nature, London, 2022. Observation year 2020 (population grid). Accessed 2026-11-03.back
  7. 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
  8. 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
  9. 5UN DESA (ed.), Sustainable Development Goal 11: make cities and human settlements inclusive, safe, resilient and sustainable (Goal page; slum population, land consumption rate, targets). United Nations, New York. Observation year 2022 (slums) and 2025 (land consumption). Accessed 2026-11-03.back
  10. 12UN-Habitat (ed.), World Cities Report 2024: Cities and Climate Action, key messages (report page; cities receive less than 20% of climate finance needed). United Nations Human Settlements Programme, Nairobi. Observation year 2024. Accessed 2026-11-03.back
  11. 6IPCC (ed.), Urban systems and other settlements, chapter 8 in Climate Change 2022: Mitigation of Climate Change, Contribution of Working Group III to the Sixth Assessment Report of the IPCC (downloaded chapter, executive summary read). IPCC, Geneva, 2022. Observation year 2020. Accessed 2026-11-03.back
  12. 15Trees halve the urban heat island effect globally but unequal benefits only modestly mitigate climate-change warming, Nature Communications (2026), open access full text, PMC. Springer Nature, London. Observation year 2026 (analysis of 8,919 large urban areas). Accessed 2026-11-03.back
  13. 4United Nations (ed.), The Sustainable Development Goals Report 2025, Goal 11 (housing, flood, local risk reduction strategies, waste collection, national urban policies). United Nations, New York. Observation year 2024 (indicator data 2010 to 2024). Accessed 2026-11-03.back
  14. 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
  15. 19Urban tree canopy fragmentation and child mortality in low- and middle-income countries, Proceedings of the National Academy of Sciences (2026), open access full text, PMC. National Academy of Sciences, Washington. Observation year 2026 (420,000 children, 57 countries). Accessed 2026-11-03.back
  16. 18The role of greenness in heat-related mortality: a systematic review and meta-analysis, Annals of Global Health (2026), open access full text, PMC. Ubiquity Press, London. Observation year 2026 (11 studies). Accessed 2026-11-03.back

Cite this chapter

Valadbaygi, S. (Ed.). (2026). Chapter 1: Cities are where the systems meet. 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

Infrastructure and its partners

Infrastructure gives pipes, dams and treatment works to water (0.6), transmission and fuel logistics to energy (0.6) and access to care to health (0.5).

W · E · I · F · H · B

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

Strongest relations in play

  • Energy → Infrastructure · power for transport and telecoms0.8
  • Water → Energy · cooling water and hydropower0.6
  • Infrastructure → Water · pipes, dams and treatment works0.6
  • 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.
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