The warming of Brussels: a city heating faster than it adapts

1. What we observe

The Brussels urban heat island. The VITO study carried out for Brussels Environment (commissioned 2017, published 2018, UrbClim model at 100 m resolution, period 1987-2016) documents the city-countryside gap in detail. In summer, the air in the centre is on average 3 °C warmer than surrounding rural areas during the day. At 11 pm, the time when the island is most pronounced, the average gap reaches 4.5 °C. In extreme conditions (clear sky, low wind, high mineralisation), the nocturnal gap can locally exceed up to 10 °C: that is an absolute maximum, stated for cities in general, not a Brussels average. The same model reveals that there are on average 3 times more intense heat periods in the centre of Brussels than in rural areas over the same period.

Spatial heterogeneity. The gap is not uniform. Highly mineralised and poorly vegetated areas (certain neighbourhoods of the pentagon, economic activity zones, surroundings of transit axes) accumulate aggravating factors: dark surfaces, absence of trees, heat rejected by buildings and engines. Forested areas (Sonian Forest, Bois de la Cambre) constitute cool islands. This mapping has been refined by Brussels Environment to identify priority intervention zones.

Tropical nights. IRM records at Uccle a progression of warm nights (minimum nocturnal temperature equal to or above 15 °C): +3.71 additional nights per decade between 1981 and 2022. These nights without recovery constitute the main factor of excess mortality during heatwaves.

Heatwaves at Uccle (long series). The official IRM definition of a heatwave requires at least 5 consecutive days with a maximum temperature equal to or above 25 °C, of which at least 3 days at 30 °C or above. Between 1901 and 2023, Uccle recorded 48 heatwaves. The 2010s are the most loaded with 10 waves. The upward trend has accelerated since the 1990s: no heatwave had been recorded between 1960 and 1975. In September 2023, the first autumn heatwave was recorded.

The June 2026 heatwave. At the time of writing this dossier, Brussels is experiencing an exceptionally early heatwave, which began on 17 June 2026, with maxima exceeding 36-37 °C and nocturnal minima not dropping below 25-27 °C in major cities. IRM placed Belgium under orange code.

2. What the studies say

Long term at Uccle. Since measurements began in 1833, Uccle has recorded a warming of +2 °C. Since 1981, the rate is +0.38 °C per decade. The years 2020, 2022, 2023 and 2024 are among the six warmest years since measurements began (Brussels Environment, state of the environment data). The maximum summer temperature increased by +0.86 °C per decade between 1981 and 2022. Confidence: official.

Excess mortality (Sciensano). Summer 2022 produced excess mortality of +5.7%, or 2,291 additional deaths: the heaviest toll in twenty years. The heatwave alert phase was activated 4 times that summer. Summer 2020 was also deadly: +1,460 additional deaths between 5 and 20 August, with a peak of 488 deaths in a single day (13 August), combining heat and ozone pollution. Confidence: official.

Combined heat and pollution. During the August 2020 heatwave, 9 days over the reference period exceeded the ozone threshold of 100 µg/m³. The official plan explicitly bears the title "intense heat AND ozone peaks": the two risks are managed jointly because they affect the same populations and reinforce each other. Confidence: official.

IPCC/AR6. A decadal heatwave (occurring on average once every 10 years in a climate without human influence) now occurs 9.4 times more often in a world at +3 °C of global warming. In Europe, deaths attributable to extreme heat could reach approximately 30,000 per year at +1.5 °C, a figure that could almost triple at +3 °C. Confidence: official.

Projections to 2070-2100 (RCP8.5 scenario). According to the CORDEX.be projections (IRM, ALARO model), reproduced in the Brussels Environment Climate sheet (January 2021), the number of days exceeding 30 °C at Uccle would increase from 4.5 per year today to nearly 20 per year by 2070-2100, under the high-emissions RCP8.5 scenario. This scenario is the most pessimistic of the four considered. Confidence: official (provided RCP8.5 and the 2070-2100 horizon are explicitly cited).

Climate analogue at 2050 (RCP4.5 scenario). The Bastin et al. study (Understanding climate change from a global analysis of city analogues, PLOS ONE 14(7): e0217592, 2019, DOI 10.1371/journal.pone.0217592) compares the future climate of 520 major cities (2050 horizon, RCP4.5 scenario) with the current climate of cities located further south. According to the study's interactive map, Canberra (Australia) is the closest designated climate analogue for Brussels. The exact pair comes from the study's map, not from a data table read line by line. Confidence: estimated.

3. What this implies

These data outline a twofold challenge. First, an immediate health risk: the increase in nights without recovery, combined with ozone pollution, affects elderly people, infants, people with cardiovascular or respiratory conditions, and homeless people. The toll of 2,291 additional deaths in 2022 is not a statistical anomaly: it is the underlying trend, confirmed over twenty years of data.

Second, a structural risk over a ten-year horizon. If the RCP8.5 scenario materialises, Brussels would shift from a rate of 4.5 heatwave days per year to around twenty by 2070-2100. This is not a distant scenario: the infrastructure, buildings and public spaces being built today will have to function in this context. The climate analogue (Canberra) illustrates the scale of change to anticipate, beyond precise figures.

4. What remains debated

Several points of uncertainty remain. The VITO 2018 mapping remains the official reference for the Brussels urban heat island: no post-2018 update has been confirmed in the sources consulted, which limits the ability to observe recent developments. The "Brussels-Canberra" pair from the Bastin et al. study comes from the interactive map and media relays: it has not been read in the primary data table of the study. Finally, the Sciensano excess mortality figures are national: a specifically Brussels breakdown has not been identified in the press releases consulted.

Sources: Brussels Environment, "Urban heat island" (VITO study 2018, UrbClim 1987-2016), https://environnement.brussels/citoyen/documentation-et-outils/etat-des-lieux-de-lenvironnement/ilot-de-chaleur, accessed 25/06/2026. IBSA / IRM, long series Uccle 1901-2023, https://ibsa.brussels/actualites/vagues-de-chaleur-a-uccle-entre-1901-et-2023-les-annees-2010-et-2020-affichent-des-records, accessed 25/06/2026. Brussels Environment, "Climate in the Brussels Region", https://environnement.brussels/citoyen/documentation-et-outils/etat-des-lieux-de-lenvironnement/le-climat-en-region-bruxelloise, accessed 25/06/2026. Sciensano, excess mortality summer 2022, https://www.sciensano.be/fr/coin-presse/la-surmortalite-durant-lete-2022, accessed 25/06/2026. Sciensano, August 2020 heatwave, https://www.sciensano.be/fr/coin-presse/une-surmortalite-importante-durant-la-canicule-du-mois-daout-2020, accessed 25/06/2026. IPCC AR6, summary WG1 and WG2 Chapter 13 (Europe), https://www.ipcc.ch/report/ar6/, accessed 25/06/2026. Brussels Environment, Climate sheet n°6 (Ronsmans, January 2021, CORDEX.be/IRM projections, RCP8.5, 2070-2100), https://environnement.brussels/media/5275/download?inline=, accessed 25/06/2026. Bastin et al., PLOS ONE 14(7): e0217592, 2019, DOI 10.1371/journal.pone.0217592, interactive climate analogue map, accessed 25/06/2026. IRM, June 2026 heatwave, https://www.meteo.be/fr/meteo/avertissements/avertissement-chaleur, accessed 25/06/2026.

1. What we observe

56% of Brussels households without a car: a counter-intuitive figure. The Region concentrates the highest non-motorisation rates in the country. According to the Statbel survey "Car ownership by household" (2024), 56.4% of Brussels households own no car, twice the Belgian average (28%), twice that of Flanders (23.6%) and more than twice that of Wallonia (24.7%). In the densest municipalities, Saint-Gilles and Saint-Josse each reach 72% of households without a car, with an average of 0.33 cars per household compared to 1.06 for the country as a whole. The Brussels average is 0.54 cars per household, down 1.8% between 2023 and 2024. Confidence: official (Statbel).

These figures do not mean that Brussels is free of car traffic. They mean that the cars present on Brussels roads are mostly those of commuters and transit traffic, not residents. Incoming flows from the periphery constitute the main lever for reducing transport-related emissions at city scale. The LEZ and Good Move dossiers document the measures underway and their results.

30% of housing from before 1919. The 2021 census (Census 2021, Statbel) indicates that 30% of Brussels housing was built before 1919, compared to 11% in Flanders and 21% for Belgium as a whole. Only Wallonia fares worse (37%). Conversely, only 5% of the Brussels stock dates from after 2011: the region has built little recently relative to its population. This old building stock, often without adequate thermal insulation, presents a double vulnerability: it overheats in summer and retains little nocturnal coolness. Confidence: official (Statbel, Census 2021).

Sealing: 53% of territory, 40% residential. Approximately 53% of regional territory is sealed (Brussels Environment estimate, state of the environment). The cadastral register (Statbel, early 2024) indicates that residential land represents 40% of Brussels cadastral territory, the highest proportion among the regions (9% national average). The built surface area grew by approximately 30 ha per year over the last decade. Confidence: estimated for the overall sealing rate (Brussels Environment); official for the cadastral residential share (Statbel).

Anthropogenic heat: air conditioning and data centres. Air conditioning, which is growing in homes and offices, has a perverse effect: it cools the interior by rejecting heat outside, into streets that are already overheated. Digital infrastructure (data centres) generates continuous thermal flows. These anthropogenic heat sources have not yet been precisely quantified at Brussels scale. Confidence: estimated (international scientific literature, not measured locally). See data centres, AI and energy.

2. What the sources say

Distinction between global and local heat. The IPCC (AR6) clearly establishes that greenhouse gas emissions contribute to global climate change. Brussels's share of this global warming is marginal: a city of 1.25 million inhabitants represents a tiny fraction of global emissions. However, the urban structure (mineralisation, density, lack of vegetation) is the main cause of the local amplification of heat, measurable in the city-countryside gap of 3 °C during the day and 4.5 °C at 11 pm (VITO/Brussels Environment, see previous chapter). These two phenomena follow distinct logics and levers. Confidence: official (IPCC AR6; VITO study for Brussels Environment).

The Air-Climate-Energy Plan (PACE) sets mitigation targets. Finally adopted in May 2023, the PACE aims for a 47% reduction in greenhouse gas emissions by 2030 (compared to 2005) and carbon neutrality by 2050. It identifies transport and buildings as the two main intervention sectors. The adaptation component (resilience against inevitable heat) is present but its objectives remain qualitative in the documents consulted: no budget dedicated to adaptation has been identified in the plan's public communications. Confidence: official for mitigation targets; estimated for the absence of a dedicated adaptation budget (absence noted, not stated as definitive).

Old building stock and territorial inequality. The 2021 Census confirms that Brussels's housing stock is structurally older than that of Flanders, with a proportion of pre-1919 buildings almost three times higher. Energy performance certificates (EPC), which fall under Brussels Environment rather than Statbel, allow identification of which buildings perform worst: the sources consulted do not provide an EPC breakdown by construction period at regional scale. Confidence: official for Census 2021; EPC data by construction period not found in sources consulted.

Traffic and LEZ: a documented correlation, a causality to clarify. The low-emission zone (LEZ) in force since 2018 aims to reduce pollutant emissions and thermal output from older vehicles. LEZ monitoring data (emission trends, transit traffic changes) are published by Brussels Environment and Brussels Mobility, and analysed in the dedicated LEZ dossier. The share of transit traffic in total kilometres travelled in the Brussels Capital Region has not been found in the sources consulted for this dossier. Confidence: official for the existence and objectives of the LEZ.

3. What this implies

The distinction between the two scales is not merely an academic precaution: it directly guides public policy. Acting on Brussels's greenhouse gas emissions (transport, heating, industry) is useful for the global climate objective, but will not reduce the local heat island in the short term. On the other hand, greening school courtyards, making soils permeable, planting trees along roads, covering dark surfaces with high-albedo coatings: these actions directly reduce the heat felt in the city, in the years that follow, independently of what happens to global emissions.

The structure of Brussels's car fleet (high proportion of households without cars) also implies that traffic reduction policies must target peripheral mobility, not only residents' practices. This is a regional-federal governance issue and a matter of cooperation with neighbouring Flemish and Walloon municipalities.

4. What remains debated

Three structural areas of uncertainty. First, the precise share of transit traffic in the volume of cars in circulation in the Brussels Capital Region: no consolidated figure was found in the sources consulted for this research pass. Second, the quantification of thermal flows from air conditioning and data centres at Brussels scale: international sources document the phenomenon but no local measurement was found. Third, the link between building age and summer thermal performance: the Census provides building age, but the precise correlation with indoor summer temperatures remains to be established through in-situ measurements in Brussels.

Sources: Statbel, "Car ownership by household", https://statbel.fgov.be/fr/themes/mobilite/circulation/possession-de-voitures-par-menage, accessed 25/06/2026. Statbel, "Construction period" (Census 2021), https://statbel.fgov.be/fr/themes/census/logement/epoque-de-construction, accessed 25/06/2026. Statbel, "Land use according to the cadastral register", https://statbel.fgov.be/fr/themes/construction-logement/occupation-du-sol-selon-le-registre-cadastral, accessed 25/06/2026. Brussels Environment, Air-Climate-Energy Plan (PACE), https://environnement.brussels/citoyen/politique-regionale/plans-strategiques-regionaux/bruxelles-reunit-air-climat-et-energie-dans-une-vision-integree, accessed 25/06/2026. IPCC AR6, https://www.ipcc.ch/report/ar6/, accessed 25/06/2026. Brussels Environment, VITO study 2018, urban heat island, https://environnement.brussels/citoyen/documentation-et-outils/etat-des-lieux-de-lenvironnement/ilot-de-chaleur, accessed 25/06/2026.

1. What we observe

Four emblematic cases illustrate the tension between public development and adaptation to heat.

The table above does not cover all Brussels construction projects; it targets those for which a documented link to urban heat or the tree canopy has been signalled in multi-confirmed sources.

At regional scale, Help4Trees and IEB report that more than sixty-two thousand standard trees were authorised for felling between 2010 and 2022, excluding the Sonian Forest, compared to approximately three thousand two hundred and fifty-four replanted. This ratio is advanced by citizen collectives and relayed by several media; it does not come from an official register. The figure of twenty-four thousand trees lost over the last five years is mentioned in other sources for the same period, with formulations varying by article. Despite the regional and municipal canopy plans (objective of no net loss by 2030 compared to 2024), tree cover is declining according to these collectives.

2. What the sources say

Schuman roundabout. Project owners: Beliris (federal) and Brussels Mobility (Region). Initial budget of thirty million euros, actual cost of approximately forty-two million euros according to the press, with a breakdown: plus five million euros for public space, plus three point four million euros for the vegetation canopy, plus four point seven million euros for security. The giant canopy/shelter, estimated at three million euros in 2021 then thirteen million euros in 2025, was abandoned by Beliris in summer 2025 to meet the June 2026 European funding deadline. On 6 November 2025, urban.brussels issued a formal notice to Beliris and Brussels Mobility: without the canopy, the construction site is in breach of planning permission. The municipality must either modify the permit (new public inquiry) or build the canopy. Confidence: estimated for costs (multi-source press); official for the formal notice (administrative act by urban.brussels).

Josaphat wasteland. On 3 November 2025, the French-speaking Brussels court of first instance ordered the Brussels Region to suspend the urbanisation and sealing of undeveloped plots of more than 0.5 hectares until the new regional land-use plan (PRAS) enters into force, at the latest by 31 December 2026. If the consortium's urbanisation project is halted, the Urban Development Company (SAU) would lose approximately thirty-one point seven million euros in revenue from the sale of phase 1 land. On 9 February 2026, the Brussels Parliament's Territorial Development committee rejected a moratorium proposal covering nine wastelands. Confidence: official (court ruling, parliamentary act).

Mediapark/Reyers. The PAD (directional development plan) Mediapark was validated by the regional government in April 2024: media hub (VRT/RTBF), approximately one thousand four hundred homes, shops and facilities. Greenpeace and IEB reported the felling of approximately one thousand trees in the Georgin wood (eight hectares), some already cut for a site access road, and contest the claim that the "eight hectares of park" announced include mineralised surfaces and perimeter entrances. The overall cost of the real estate project was not found in the sources consulted. Confidence: unconfirmed (figure of one thousand trees advanced by Greenpeace/IEB, not confirmed by an official assessment).

Avenue de la Toison d'Or. Announced envelope of sixteen million euros, described as "not guaranteed" in the sources consulted: the Region must find the budget. Permit obtained in 2022; no construction started four years later. A retailers' appeal constitutes the last identified obstacle. Thirty-eight new trees are planned in the plan, but this is a project figure not yet realised. Confidence: estimated (envelope and tree figure from Brussels Mobility documents and press).

De-mineralisation counter-examples. Flagey square (Ixelles) was greened at approximately one million euros, with about one hundred trees planted, aiming to de-seal a historically very mineral space. The Ré-création Operation (Brussels Environment) targets forty-three thousand and ninety-two square metres of school courtyards to be de-sealed in nineteen Brussels establishments, for an envelope of approximately five million euros (approximately three hundred thousand euros per school). Four projects were completed by summer 2025, eleven launched in the second half of 2025. Confidence: estimated (regional data and multi-source press, surface figures not yet verified against final assessment).

3. What this implies

The documented cases outline a recurring cycle: public spaces were concreted or kept mineral during earlier works, and new public funds today finance their greening in response to heatwaves. The sources consulted do not consolidate a total figure for this "double expenditure" at regional scale; figures remain case by case.

The tension between climate adaptation and other public objectives is clear in two cases. At Josaphat, the court arbitrated between sealing and protection of natural spaces, at the potential cost of thirty-one point seven million euros for the SAU. At Schuman, the decision to abandon the canopy to meet a European funding deadline leaves a forty-two million euro construction site without shade, with an ongoing planning infringement procedure.

The felling question points to a data deficit. No single regional tree register (felled, planted, maintained) currently exists: this is precisely what Help4Trees and IEB are requesting in their petition. Without a consolidated register, it is impossible to verify whether the regulatory objective of "no net loss of tree cover by 2030" is on track to be met.

4. What remains debated

Several points remain open. First, the exact status of the felling permits: the sixty-two thousand trees mentioned by Help4Trees/IEB are authorisations granted, not necessarily fellings carried out, and the gap between the two is not quantified in the available sources. Second, the outcome of the Schuman roundabout permit: urban.brussels has issued Beliris a formal notice, but the concrete follow-up (permit modification, canopy construction, or filing without further action) is not documented at the time of writing. Third, the actual nature of the green spaces announced at Mediapark: the share that is effectively non-mineralised within the "eight hectares of park" is not established by an official document.

Sources: bx1.be (fellings, Toison d'Or, Ré-création); lavenir.net (Schuman canopy, Toison d'Or, Mediapark, Flagey); bruxellestoday.be (Schuman costs, canopy); dhnet.be and lavenir.net (urban.brussels issues formal notice to Beliris, 6 November 2025); lalibre.be and lavenir.net (Josaphat, ruling of 3 November 2025 and SAU loss of 31.7 M€); dhnet.be and bx1.be (moratorium on 9 wastelands rejected, 9 February 2026); rtbf.be (Mediapark, Greenpeace, one thousand trees); ieb.be (Mediapark, fellings); lavenir.net and moustique.be (Flagey, greening); rtbf.be and bx1.be (Ré-création Operation, nineteen schools, 43,092 m²); be.brussels (no net loss objective 2030). Date of access: 25 June 2026. Confidence: official for the urban.brussels formal notice and the Josaphat ruling; estimated for Schuman, Toison d'Or and Ré-création costs; unconfirmed for felling figures (permits vs. actual, source: citizen collectives) and the Mediapark one-thousand-trees figure.

1. What we observe

The PACE adopted in 2023, but its adaptation axis remains underdeveloped. The Brussels government definitively adopted the Air-Climate-Energy Plan (PACE) on 27 April 2023, after three readings. Anchored in the COBRACE (Brussels Code on Air, Climate and Energy Management), it constitutes the regional climate policy framework document: mitigation (target of -47% in greenhouse gas emissions by 2030 compared to 2005, carbon neutrality by 2050) and adaptation. Axis 6 of the PACE groups the adaptation measures against inevitable heat: improving territorial resilience through soil permeability, integrated rainwater management, greening of dense neighbourhoods and creation of cool zones against urban heat islands. This axis is the least developed in the plan in the public documents consulted, with qualitative, non-quantified objectives. No budget dedicated to adaptation has been identified in official communications. Confidence: official for the plan's adoption and mitigation targets; estimated for the absence of a dedicated adaptation budget (as noted by Inter-Environnement Bruxelles, not contradicted by an official source).

The heatwave plan: 3 phases, fragmented management, voluntary in nature. The regional "heat and ozone peaks" plan is the health device facing heatwaves. It operates in 3 phases: vigilance (from 15 May to 30 September, by default), warning (triggered by Cocom when the cumulative temperature exceeds a threshold over 5 days), alert (decided by the federal Risk Management Group, chaired by the SPF Public Health). Raising awareness among vulnerable groups (elderly people, infants, chronically ill people, dependent and isolated individuals) falls to Cocom and its partners. This plan has been in force since 2006, created in the wake of the August 2003 heatwave. Its non-binding nature distinguishes it from the winter Plan Grand Froid, which provides more structured obligations. Confidence: official (Cocom/Vivalis, Brussels Environment, IRCEL-CELINE).

Urban planning framework tools: Good Living RRU and Water Management Plan. The Good Living regional urban planning regulation introduces the biotope surface coefficient (CBS+) to measure the biodiversity and permeability of projects, and imposes provisions on permeable surfaces, green roofs, rainwater collection tanks and high-albedo materials (light colours, low heat absorption) to limit heat islands. The 2022-2027 Water Management Plan follows the "sponge city" logic: infiltrate and store water where it falls, complementing the blue network (regional programme for restoring watercourses and wetlands, active since 1999). These mechanisms are active and produce effects, but they are sectoral: they act on new buildings and renovations, not on the existing stock. Confidence: official.

PACE/Canopy Plan distinction. The Canopy Plan 2020-2030 is a municipal greening plan (City of Brussels), comprising objectives for garden-forests, urban forests and a Tree Charter. It must not be confused with the regional greening policy carried by Brussels Environment. These two levels act on distinct territories with separate budgets. Confidence: official.

2. What the sources say

The urban heat island data deficit. The official mapping of the Brussels urban heat island rests on the study commissioned from VITO by Brussels Environment (UrbClim model, 100 m resolution, reference period 1987-2016, published 2018). No update to this mapping has been confirmed in the sources consulted as of 25 June 2026. The press reported in July 2025 that this data was described as "relatively old". This absence of update limits the ability to measure recent changes in the heat island, to target priority intervention zones, and to evaluate the effectiveness of measures already taken. Confidence: estimated (absence noted in sources, not a definitive assertion).

The tree register: a documented request, without confirmed official follow-up. Help4Trees and Inter-Environnement Bruxelles (IEB) have formally requested the creation of an open regional tree register. At the time of writing, no such register is publicly accessible at regional scale. Without a consolidated register, data on tree cover remains fragmented between felling permits granted (urban.brussels), trees planted by Brussels Environment and trees managed by municipalities. Confidence: estimated (absence of register noted in sources consulted).

Brulocalis and the unpreparedness finding. The Brussels municipal federation (Brulocalis) has estimated that Brussels is not ready to face climate change. This position, advanced by the representative association of the 19 municipalities, points in particular to the lack of resources for municipalities to fulfil adaptation missions (cooling of public spaces, reception of vulnerable populations, heat island management in dense areas). Confidence: estimated (position of a representative association, not contradicted by an official source in the sources consulted).

The 2016 Nature Plan: biodiversity, not direct adaptation. The Nature Plan, adopted by the government on 14 April 2016, includes 7 major objectives and 27 measures to the 2050 horizon. Its central objective is that every Brussels resident has access to a green space of more than 1 ha within 400 m, or less than 1 ha within 200 m of their home. This plan contributes indirectly to the fight against heat islands through greening, but it is not a climate adaptation plan in the strict sense. Confidence: official.

3. What this implies

The overall picture is that of an institutional response that exists but remains fragmented, under-budgeted in its adaptation component, and blind to some of its results for lack of up-to-date data.

Three shortcomings reinforce each other. First, the absence of an identified adaptation budget: without a dedicated budget line, coordination between Brussels Environment, Cocom, safe.brussels and the municipalities rests on sectoral mechanisms that are not articulated. Second, the voluntary nature of the heatwave plan: recommendations to nursing homes, schools and health operators are not enforceable, creating unequal implementation across municipalities and operators. Third, the data deficit: without an update to the heat island mapping and without a tree register, it is impossible to verify whether the measures undertaken (planting, de-mineralisation, CBS+) are effectively reducing heat in the most exposed neighbourhoods.

The fragmented coordination described in this chapter is addressed in more detail in the next chapter ("Who decides, who pays, who passes the buck").

4. What remains debated

Several points of uncertainty merit follow-up.

The adaptation budget: the absence of an identified dedicated budget line does not mean the absence of expenditure. It is possible that resources are committed within the Brussels Environment, Nature Plan or Water Management Plan envelopes without being explicitly labelled as "adaptation". A budgetary reconstruction would exceed the scope of this dossier.

The binding nature of the heatwave plan: the question of revising the plan to introduce obligations (closure of non-air-conditioned nursing homes from the warning stage, mandatory school protocols) is advanced by public health actors but has not resulted in any change to date. The precise positions of the levels of government have not been found in official acts.

The update of the VITO mapping: Brussels Environment regularly commissions state of the environment studies. The question of an update to the UrbClim study is raised but no confirmed commission was found in the sources consulted.

Sources: Brussels Environment, Air-Climate-Energy Plan (PACE), adopted 27 April 2023, https://environnement.brussels/citoyen/politique-regionale/plans-strategiques-regionaux/bruxelles-reunit-air-climat-et-energie-dans-une-vision-integree, accessed 25/06/2026. Full PACE PDF, https://document.environnement.brussels/opac_css/elecfile/PACE_FR.pdf, accessed 25/06/2026. Maron-Trachte.brussels, final adoption of PACE, 03/05/2023, https://maron-trachte.brussels/2023/05/03/climat-le-gouvernement-bruxellois-adopte-definitivement-son-plan-air-climat-energie-et-confirme-ses-hautes-ambitions/, accessed 25/06/2026. Cocom/Vivalis, heat and ozone peaks plan, https://www.vivalis.brussels/fr/prevenir-et-agir/sante-et-environnement/plan-forte-chaleur-et-pics-dozone, accessed 25/06/2026. Brussels Environment, heat and ozone peaks plan, https://environnement.brussels/citoyen/politique-regionale/plans-strategiques-regionaux/plan-forte-chaleur-et-pics-dozone, accessed 25/06/2026. IRCEL-CELINE, FAQ heat plan, https://www.irceline.be/fr/documentation/faq/quest-ce-que-le-plan-forte-chaleur-et-pics-dozone-et-quelles-sont-les-differentes-phases, accessed 25/06/2026. Brussels Environment, Nature Plan, https://environnement.brussels/citoyen/nos-actions/plans-et-politiques-regionales/le-plan-nature, accessed 25/06/2026. Brussels Environment, Water Management Plan 2022-2027, https://environnement.brussels/sites/default/files/user_files/resume_non_technique_pge_fr.pdf, accessed 25/06/2026. Brussels Environment, blue network, https://environnement.brussels/citoyen/politique-regionale/rapports-des-projets-environnementaux/gestion-du-maillage-bleu-bruxellois, accessed 25/06/2026. Brussels Environment, VITO study 2018 (urban heat island mapping, data 1987-2016), https://environnement.brussels/citoyen/documentation-et-outils/etat-des-lieux-de-lenvironnement/ilot-de-chaleur, accessed 25/06/2026. City of Brussels, Canopy Plan 2020-2030, https://www.bruxelles.be/plan-canopee-2020-2030, accessed 25/06/2026. Sustainable Building Guide (CBS+, Good Living RRU), https://guidebatimentdurable.brussels/favoriser-biodiversite/reglementation, accessed 25/06/2026.

1. What we observe

Climate competence in Brussels reads like a grid: eight themes, five levels of government. The matrix below summarises who is competent for what.

No line is filled by a single level. Even the heatwave plan, which appears sanitary, mobilises the federal (alert), Cocom (awareness-raising and nursing homes), the Region (coordination of adaptation via Brussels Environment) and municipalities (schools, public welfare centres, drinking water points). This dispersion is the starting point: it is not an anomaly, it is the Belgian institutional structure applied to a cross-cutting risk.

2. What the sources say

Several situations of responsibility-passing are documented in the press and institutional sources.

• Interfederal heatwave plan. The federal level advocates for a coordinated heatwave plan between levels of government, but this project runs into community reluctance: the economic press summarised the episode by noting that "heatwave management awakens old community demons", with Flanders not seeking an interfederal framework. Confidence: unconfirmed (press reading, no official act published).
• School heatwave. Asked about school closures or adaptations in the event of extreme heat, the Minister of Education of the Federation Wallonia-Brussels referred the decision to "organising authorities", that is the operators managing each establishment (municipalities, networks, institutions). Competence over school buildings and the school calendar remains with the communities, execution at local level. Confidence: unconfirmed (declaration relayed by the press).
• Cars. The Region manages the low-emission zone and the mobility plan, but vehicle taxation and registration remain federal: a regional lever on emissions coexists with a non-aligned federal fiscal lever. Confidence: official (competence distribution).
• Homeless people and public welfare centres (CPAS). The federal unemployment reform is shifting people excluded from benefits towards the social integration income, hence towards municipal public welfare centres (CPAS), without compensation deemed sufficient by CPAS federations. The on-the-ground burden rises to municipal level during heat episodes. Detail in the Brussels CPAS dossier. Confidence: official (reform in force).

3. What this implies

The funding thread mirrors the competence thread.

On the regional side, adaptation falls within an austerity budget framework announced for 2025-2029, and the adaptation component of the regional plan (axis 6 of the Air-Climate-Energy Plan, the PACE) has no clearly identified dedicated budget in the sources consulted: coordination is shared between Cocom (health), Brussels Environment (adaptation) and safe.brussels (crisis), without an isolated "adaptation" budget line. Confidence: estimated (absence of a dedicated figure noted, not an absence of expenditure).

On the European side, a lever exists but remains blocked upstream. The European Union's Social Climate Fund provides 1.659 billion euros for Belgium over 2026-2032, of which approximately 226.5 million euros directed towards Brussels. This payment is delayed, not lost: it is conditional on the submission of a national social climate plan, and the European deadline is set at 30 June 2026. As long as the national plan is not submitted, the funds are not released. Confidence: official (EU amounts and deadline); the "delayed" characterisation is factual and distinct from a loss.

On return on investment, the international literature advocates for investment in adaptation and urban greening: the World Resources Institute (WRI) estimates the return on investment of adaptation and urban trees at more than three dollars per dollar invested, at international scale. This ratio is not a Brussels measurement and does not translate mechanically into local euros: it serves as an order-of-magnitude benchmark, not a regional figure. Confidence: estimated (international study, not transposed to Brussels).

4. What remains debated

Three areas of uncertainty remain.

First, the exact status of the interfederal heatwave plan project: no official act published allows us to say whether it has been abandoned, suspended or is under negotiation, beyond press readings. Second, the real adaptation budget: the absence of an identified dedicated line does not mean an absence of expenditure, and the share of adaptation within existing envelopes (Brussels Environment, water plan, nature plan) remains to be reconstructed. Third, the fate of the Social Climate Fund: the deadline of 30 June 2026 is approaching, and the effective submission of the national plan, a condition for releasing the Brussels share, is not confirmed at the time of writing.

Sources: Trends-Tendances (interfederal heatwave plan episode, press reading); declarations relayed by the press (school heatwave, Minister of Education of the FWB); Brussels Environment, Air-Climate-Energy Plan (PACE), adaptation component; European Commission documents on the Social Climate Fund (Belgium and Brussels amounts, 30 June 2026 deadline); World Resources Institute (adaptation ratio, international scale). Date of access: 25 June 2026. Confidence: official for competence distribution, Social Climate Fund amounts and the unemployment reform; estimated for the absence of a dedicated adaptation budget and the WRI ratio as transposed; unconfirmed for responsibility-passing episodes relayed by the press.

1. What we observe

The overlap of density, poverty and heat. Statbel data (density 2026, fiscal income 2023) make it possible to map social vulnerability to heat. Saint-Josse-ten-Noode has the highest density in Belgium (23,266 inhabitants/km²) and the lowest average income per inhabitant (11,082 euros/inhabitant). Koekelberg (19,103 inhabitants/km²), Molenbeek-Saint-Jean (16,359 inhabitants/km²) and Schaerbeek (16,362 inhabitants/km²) combine high density, heavy mineralisation and below-average national incomes. Conversely, the least dense municipalities (Watermael-Boitsfort: 1,949 inhabitants/km²) are also those with the most extensive tree canopy and green spaces. Confidence: official (Statbel).

Homeless people: 9,777, up 24.5%. The 7th Bruss'help census (night of 6 November 2024, results published April 2025) counted 9,777 homeless people in the Brussels Region, of whom approximately 1,000 living on the street in the strict sense, 1,991 women and 1,678 minors. The increase is +24.5% since 2022 (7,134 people). Confidence: official (Bruss'help, primary source).

Deaths of homeless people. The Collectif Les Morts de la Rue (Diogenes association) counted at least 81 homeless people who died in Brussels in 2024 (68 men, 13 women, of whom 48 were living on the street at the time of death). This figure is considered a floor: the collective itself acknowledges probable under-counting. Confidence: unconfirmed (associative census, probable under-counting).

Seniors: confirmed excess mortality in Brussels. Sciensano (Be-MOMO surveillance) documented for summer 2025 (12 May to 5 October 2025) Brussels excess mortality of +3.3%, or 98 additional deaths compared to the expected period: Brussels was the most affected region in Belgium. Three heatwaves produced marked peaks: +7.6% (105 deaths) from 18 to 22 June 2025, +4.0% (86 deaths) from 25 June to 2 July 2025, and +12.9% (175 deaths) from 7 to 15 August 2025. At Belgian scale, the 65-84 age group is the most affected (+1.5%, or 253 additional deaths over the 2025 summer season). Confidence: official (Sciensano, national surveillance).

Children in dilapidated schools. The Federation Wallonia-Brussels (FWB), competent for education, does not impose a binding protocol for school closure in the event of a heatwave. The circular issued by the FWB Minister of Education for the June 2026 episode was described as "dangerous" by the CGSP and CSC unions, who describe "inhuman temperatures in classrooms". The municipality of Etterbeek chose to suspend classes in its municipal establishments every afternoon from 22 to 26 June 2026 (examinations maintained in the mornings). The Ligue des familles denounced an "impossible equation" for parents, 44% of whom have only the legal 20 days of annual leave. Confidence: official for documented union positions and the Etterbeek municipal decision; unconfirmed for the FWB circular (relayed by the press).

One in five Brussels residents without nearby green space. IBSA (Focus n°56, March 2023), in collaboration with Brussels Environment, calculated that approximately 264,000 inhabitants of the Region, or 22% of the population, live in an area lacking nearby green space (public green space within 400 m, or within 200 m if under 1 ha). This deficit is not uniformly distributed: it concentrates in the densest municipalities of the poverty crescent. Confidence: official (IBSA/Brussels Environment).

2. What the sources say

The winter/summer asymmetry denounced by field actors. The Infirmiers de rue (street nurses) have documented and formalised the finding: "Winter 'plans' are put in place every year, but few measures are taken in heatwave contexts." The organisation advocates for housing as the structural response to climate risks for homeless people, access to care remaining complicated by the administrative requirement of an address. Medecins du Monde highlights the same obstacles: complicated access to care, need for permanent nursing posts. L'Ilot reports that day centres are saturated in summer, with no notable extension of summer hours or capacities. Confidence: official (organisational positions, primary sources).

The 2026 summer response mechanism: reinforced but limited. Samusocial has been operating since 2 February 2026 a shelter at WTC4 (100 places increased to 130 from 5 May 2026 and extended to end September 2026), for isolated men. The City of Brussels activated its heat plan on 23 June 2026: free helpline 0800/35.550 for elderly and isolated people, distribution of 500 water bottles, mobilisation of Bruciteam, Herscham team, community wardens and Samusocial. Samusocial patrols include distribution of water and maps of public fountains. These measures represent progress compared to previous years, but no specific budget figure for the 2026 homeless heat plan is available. Confidence: official (Samusocial, City of Brussels via press).

Nursing homes: regulatory obligation, compliance not publicly verified. Iriscare (bicommunal public interest body, competent for the 113 accredited nursing homes in Brussels) launched in June 2026 a telephone outreach campaign to establishments to verify the implementation of measures. The regulatory obligation in force requires an air-conditioned living area large enough to accommodate all residents, with a maximum difference of 8 °C between outdoor and indoor temperature (risk of thermal shock). However, the number of establishments actually compliant is not the subject of an official publication accessible in the sources consulted. Confidence: official for the obligation and the Iriscare campaign; estimated for actual compliance (documented gap).

3. What this implies

Vulnerability to heat in Brussels is not random: it follows the map of poverty and density. The most exposed municipalities are also those whose public welfare centres (CPAS) are the most in demand and whose resources are the most limited. The Brussels CPAS dossier details the triple financial shock affecting these structures. The Brussels BIM dossier explores the links between health coverage, incomes and affected neighbourhoods.

The asymmetry between the robustness of winter plans (emergency shelter, sleepless night, protocols) and the fragility of summer mechanisms reveals an implicit trade-off: heat has killed more than cold in Brussels since the 2000s, but institutional responses remain less structured for summer. This gap has been documented by field organisations for several years without plans having evolved towards a binding character.

4. What remains debated

Several gaps persist. The number of nursing homes actually equipped with a compliant air-conditioned space is not made public: the obligation exists, but its compliance is not the subject of a consolidated accessible report. The mechanism for identifying vulnerable people remains fragmented between public welfare centres, municipalities, Vivalis/Iriscare and the City's helpline: no centralised regional register (analogous to the French heatwave register) has been identified in the sources consulted. Finally, the precise health impact of the June 2026 heatwave on Brussels populations will not be known until Sciensano data are published, probably in autumn 2026.

Sources: Bruss'help, 7th census, preliminary report (night of 6 November 2024, published April 2025), https://brusshelp.org/images/Rapport_Preliminaire_denombrement_FR.pdf, accessed 25/06/2026. Diogenes / Collectif Les Morts de la Rue, 2024 assessment, https://www.diogenes.brussels/fr/pages/23-collectif-les-morts-de-la-rue, accessed 25/06/2026. RTBF, "81 homeless people died in Brussels in 2024", https://www.rtbf.be/article/morts-de-la-rue-une-ceremonie-pour-les-81-personnes-sans-abri-decedees-a-bruxelles-en-2024-11554135, accessed 25/06/2026. Sciensano, Be-MOMO surveillance summer 2025, https://www.sciensano.be/en/biblio/surveillance-de-la-mortalite-toutes-causes-confondues-en-belgique-flandre-wallonie-et-bruxelles-10, accessed 25/06/2026. Iriscare, "Extreme heat: Iriscare protects vulnerable elderly people", 23/06/2026, https://www.iriscare.brussels/fr/2026/06/23/fortes-chaleurs-iriscare-protege-les-aines-vulnerables/, accessed 25/06/2026. IBSA, Focus n°56, "The challenge of green spaces in the city", March 2023, https://ibsa.brussels/sites/default/files/publication/documents/Focus-56v5_FR_0.pdf, accessed 25/06/2026. Statbel, population density (01/01/2026), https://statbel.fgov.be/fr/themes/population/structure-de-la-population/densite-de-la-population, accessed 25/06/2026. Statbel, fiscal statistics 2023 (average income Saint-Josse-ten-Noode), https://statbel.fgov.be/en/news/fiscal-statistics-2023-total-net-taxable-income-all-inhabitants-nearly-eu275-billion, accessed 25/06/2026. Infirmiers de rue, "Heatwave and homelessness: watch out for heat stroke", https://www.infirmiersderue.be/fr/actualites/canicule-et-sans-abrisme-attention-au-coup-de-chaud, accessed 25/06/2026. Samusocial, "Emergency shelter: extension of the WTC device", 27/04/2026, https://samusocial.be/hebergement-durgence-prolongation-du-dispositif-wtc-et-evolution-du-projet-daccueil-pour-les-hommes-isoles/, accessed 25/06/2026. RTBF, "Heatwave: Brussels reinforces its assistance", 23/06/2026, https://www.rtbf.be/article/canicule-bruxelles-renforce-son-aide-l-ilot-alerte-sur-le-sans-abrisme-11745980, accessed 25/06/2026. BX1, "Heatwave: the City of Brussels reinforces its assistance", 23/06/2026, https://bx1.be/categories/news/canicule-la-ville-de-bruxelles-renforce-son-aide/, accessed 25/06/2026. BX1, school heatwave circular, https://bx1.be/categories/news/chaleur-dans-les-ecoles-une-circulaire-dangereuse-selon-deux-syndicats-bruxellois/, accessed 25/06/2026. BX1, Etterbeek suspends classes, https://bx1.be/categories/news/canicule-etterbeek-suspend-les-cours-lapres-midi-dans-ses-ecoles-communales/, accessed 25/06/2026. L'Avenir, Ligue des familles (44%), 24/06/2026, https://www.lavenir.net/actu/societe/2026/06/24/la-fin-dannee-est-plus-tendue-que-jamais-pour-les-parents-un-conge-de-conciliation-OLBVMLZSVZAAXBJSJGHPTNKFLI/, accessed 25/06/2026.