Burned area
satellite only4,238ha
Perimeter published by GWIS (Copernicus).
- Source
- GWIS (Copernicus)
- Date
- 18 Sept 2021 – 28 Sept 2021
+− cross-check
No official record is matched to this page to compare it with.
BR · Brazil · –
Unaí fire, 18 September 2021 Unaí
Out · last detection 28 Sept 2021, 16:30 UTC
The fire started on 18 September 2021 in Unaí, Brazil, and satellites saw it burning for 11 days. Copernicus’s global GWIS system rebuilt a burnt perimeter of 4,238 hectares from heat detections, spread across a single municipality.
It is the 98th largest in Minas Gerais since 2016 (of 210 with a page). Number 502 in Brazil in 2021, of 814.
The power measured by the satellite is low (21.2 MW in the strongest hotspot), more typical of grass or stubble burning, or a slow surface fire, than of a large crown fire.
Use this data
Compare with…
Suggestions: Niquelândia · 2025Unaí · 2024Unaí · 2016Unaí · 2025
Use this data
Fire page data · version 2026-10-25matches the official recordwith caveatssatellite onlymodel
When copying, the sentence is
Tick the figures you want: they make up the lede and the CSV.
Duration by satellite
satellite only11days
18 Sept 2021 to 28 Sept 2021: first and last day with fire on the page.
- Source
- GWIS (Copernicus) · NASA FIRMS · VIIRS
- Date
- last detection: 28 Sept 2021, 16:30 UTC
+− cross-check
Satellites pass a few times a day and cloud or smoke can hide the fire: a lack of detections is not an official extinction. Each country’s emergency service declares a fire contained or out.
Start
satellite only18 Sept 2021
First day with fire seen by the satellites or the perimeter.
- Source
- GWIS (Copernicus) · NASA FIRMS · VIIRS
- Date
- 18 Sept 2021
+− cross-check
No official record is matched to this page, so the alert time and the cause are not known here.
Hotspots
satellite only168
VIIRS detections at 375 m. Most intense hotspot: 21 MW.
- Source
- NASA FIRMS · VIIRS (Suomi NPP)
- Date
- 18 Sept 2021 – 28 Sept 2021
+− cross-check
There is no official record to compare with. Each hotspot is a pixel detected in one satellite pass, not a separate fire.
The worst day
satellite only194MW
Total radiative power on 19 September 2021; hotspots that day: 28.
- Source
- NASA FIRMS · VIIRS (FRP)
- Date
- 19 Sept 2021
+− cross-check
Fire radiative power (FRP) measures the energy the fire gives off when the satellite passes. Added up by day, it compares intensity, not area.
Danger at the start
model51.5FWI · extreme
Fire Weather Index (Canadian system) computed by WorldFires for the day the fire started. Consecutive days without rain before: 60.
- Source
- WorldFires calculation (Canadian FWI system)
- Date
- 18 Sept 2021, local noon
- Model
- ERA5 0,25° (ECMWF · Copernicus C3S) · Open-Meteo.com
+− cross-check
This is an index computed from weather model data, not a measurement of the fire nor an official warning. Danger warnings are issued by each country’s authority. Emergency number and official warnings
Weather during the fire
model36.7°C · 17% RH
High of 36.7 °C and minimum humidity of 17% on 22 September 2021; gusts of 36 km/h on 18 September 2021.
- Source
- weather model at the fire’s grid cell
- Date
- 18 Sept 2021 – 28 Sept 2021
- Model
- ERA5 0,25° (ECMWF · Copernicus C3S) · Open-Meteo.com
+− cross-check
These are model values for a cell of about 25 km, not from a weather station: they may differ from what was measured on the ground.
This page’s change log has been kept since 24 October 2026: every night what it publishes is compared and the difference is logged. Anything earlier is reconstructed from each source’s date and marked as reconstructed.
Show
-
· reconstructed weatherWeather and FWI computed from the ERA5 reanalysis
-
logLast day with fire: 24 September 2021 → 28 September 2021.
-
· reconstructed GHSLPopulation and built-up area computed
What was saved on 25 October 2026
Every night a snapshot of what the page shows is saved. If anything changes, it appears in the list as a log entry.
- Area
- 4,238 ha
- Dates
- 18 Sept 2021 – 28 Sept 2021
- Name
- Unaí
- Official record
- —
Versioned permanent link
https://worldfires.org/en/fire/unai-2021-09-2?v=2026-10-25A version keeps the area, dates, name and official record; the area as it was logged (changes under 2% are not logged). The map, hotspots and weather always show today’s data.
Citation
A lede of about 60 words figures only, no adjectives
CSV for this fire unai-2021-09-2.csv · daily, no individual hotspots
| fecha | focos_viirs | frp_mw | tmax_c | tmin_c | hr_min_pct | viento_max_kmh | racha_max_kmh | precip_mm | fwi | clase_fwi | dentro_del_incendio |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2021-09-18 | 1 | 4 | 31.1 | 14.8 | 18 | 15.8 | 36.4 | 0 | 51.5 | extremo | 1 |
| 2021-09-19 | 28 | 194 | 34 | 14.3 | 15 | 11.4 | 27.4 | 0 | 54.5 | extremo | 1 |
| 2021-09-20 | 34 | 85 | 34.8 | 21 | 19 | 12 | 29.5 | 0 | 57.9 | extremo | 1 |
| 2021-09-21 | 36 | 92 | 35.9 | 20.8 | 19 | 11 | 27 | 0 | 50.4 | extremo | 1 |
| 2021-09-22 | 28 | 81 | 36.7 | 20.8 | 17 | 11.2 | 25.9 | 0 | 47.2 | muy_alto | 1 |
| 2021-09-23 | 20 | 93 | 32.7 | 22.3 | 33 | 15.5 | 36 | 0 | 45.4 | muy_alto | 1 |
| 2021-09-24 | 6 | 22 | 32.4 | 20.5 | 31 | 13.3 | 29.2 | 0 | 37.7 | alto | 1 |
| 2021-09-25 | 0 | 0 | 30.5 | 18.9 | 34 | 7.5 | 23 | 0 | 28.4 | alto | 1 |
| 2021-09-26 | 0 | 0 | 29.5 | 20.1 | 39 | 9 | 28.1 | 0 | 32 | alto | 1 |
| 2021-09-27 | 11 | 48 | 31.9 | 19.2 | 26 | 9.6 | 27.7 | 0 | 40.8 | muy_alto | 1 |
| 2021-09-28 | 4 | 21 | 32.2 | 17.7 | 28 | 12.1 | 31.3 | 0 | 38.7 | muy_alto | 1 |
| 2021-09-29 | 0 | 0 | 33.1 | 22.1 | 25 | 12.2 | 28.8 | 0 | 40.2 | muy_alto | 0 |
| 2021-09-30 | 0 | 0 | 33.5 | 18.4 | 29 | 8.9 | 20.5 | 0 | 35.7 | alto | 0 |
| 2021-10-01 | 0 | 0 | 33.2 | 20.9 | 32 | 13.4 | 21.2 | 0 | 38.8 | muy_alto | 0 |
| 2021-10-02 | 0 | 0 | 31.1 | 18.7 | 33 | 11.1 | 30.6 | 0 | 37.6 | alto | 0 |
| 2021-10-03 | 0 | 0 | 33.4 | 18.6 | 31 | 9.2 | 26.3 | 0 | 35.8 | alto | 0 |
| 2021-10-04 | 0 | 0 | 34.4 | 21.8 | 26 | 8.2 | 23 | 0 | 37.9 | alto | 0 |
| 2021-10-05 | 0 | 0 | 34.9 | 19.9 | 23 | 11.8 | 31 | 0 | 40.8 | muy_alto | 0 |
| 2021-10-06 | 0 | 0 | 34.2 | 22.2 | 22 | 16.6 | 39.6 | 0 | 56.2 | extremo | 0 |
| 2021-10-07 | 0 | 0 | 34.5 | 21.7 | 28 | 14.9 | 33.8 | 0 | 49.5 | muy_alto | 0 |
| 2021-10-08 | 0 | 0 | 34.1 | 21.7 | 27 | 15.2 | 37.1 | 0 | 46.9 | muy_alto | 0 |
It is generated in your browser from this page’s data: one file per fire, aggregated by day and without individual hotspots.
Live widget for your story
It updates itself while the fire is still active and links to this page. Free, with the attribution shown at the bottom.
Sources for this page: GWIS (Copernicus), NASA FIRMS (VIIRS), ERA5 (ECMWF/Copernicus C3S) · Open-Meteo.com (CC BY 4.0), GHSL (JRC). Open-Meteo.com · How we build fire pages: methodology
- Burnt area
- 4,238ha
- GWIS perimeter (Copernicus)
- Duration
- 11days
- 18 Sept 2021 – 28 Sept 2021
- Municipalities hit
- 1
- municipalities
- Started on
- 18 Sept
- 2021
- Heat detections
- 168
- in a single hotspot: 21 MW
- Danger at start
- 52
- Extreme · FWI index
- Average daily power
- 71MW
- detected power per day, on average
Where it burned
HOTSPOTS BY DAY
18 Sept28 Sept
28 Sept 2021
How it evolved, day by day
19 Sept
22 Sept
24 Sept
28 Sept
Fire radiative power detected each day, in megawatts, and number of hotspots. The magenta bar marks the peak day.
The weather it burned in
37°high
36km/h · peak gust
15%lowest humidity
It had gone more than two months without rain (1 mm or more) when it started.
This area had burned before
71% of the perimeter overlaps earlier fires recorded since 2016: 3,008 ha in 2016, 42 ha in 2020.
How big is it?
London boundary: geoBoundaries · Office for National Statistics (Open Government Licence v3.0).
Paris boundary: geoBoundaries · Institut national de l'information géographique et forestière (IGN-F) (Etalab Open License 2.0).
Madrid boundary: geoBoundaries · Open Data ESRI, IGN Central Registry of Cartography Area (CC BY 4.0).
Berlin boundary: geoBoundaries · Federal Agency for Cartography and Geodesy (dl-de/by-2-0).
This compares size, not location: both shapes are at the same scale, north up, centred on each other.
What happened to each town
-
4,262 ha reached on 18 Sept0.5 %
Burnt area inside each municipality, from crossing the GWIS perimeter with administrative boundaries. The distance runs from the point marking the centre of each area to the nearest fire: staying a kilometre away does not mean it reached the houses.
People and buildings inside the perimeter
GHSL 2020Built-up area0.20 ha
Residents< 20
Inside the perimeter there were about 0.20 hectares of built-up land and almost nobody lived there (GHSL 2020, satellite-based estimate).
This is an estimate on 100 m cells, made from satellite imagery and census data: it does not mean that homes burned or that anyone was harmed. The perimeter also contains land that never burned.
Source: Global Human Settlement Layer (GHS-BUILT-S and GHS-POP R2023A), European Commission Joint Research Centre (JRC), © European Union, CC BY 4.0. Sum inside the perimeter computed by WorldFires. human-settlement.emergency.copernicus.eu
The weather day by day
ECMWF ERA5 reanalysis at the fire location, the standard reference for past weather, and the Canadian Fire Weather Index (the same system Copernicus uses), computed by WorldFires from that data. Days after the fire run until the first rain.
Open-Meteo.com (CC BY 4.0) · Copernicus Climate Change Service (ERA5)
Started with 60 days without rain: 55 % of the area in Brazil
| Day | High | Min. humidity | Peak gust | Rain | Danger (FWI) |
|---|---|---|---|---|---|
| 18 Sept | 31.1 °C | 18 % | 36 km/h | 0.0 mm | Extreme 52 |
| 19 Sept | 34.0 °C | 15 % | 27 km/h | 0.0 mm | Extreme 54 |
| 20 Sept | 34.8 °C | 19 % | 30 km/h | 0.0 mm | Extreme 58 |
| 21 Sept | 35.9 °C | 19 % | 27 km/h | 0.0 mm | Extreme 50 |
| 22 Sept | 36.7 °C | 17 % | 26 km/h | 0.0 mm | Very high 47 |
| 23 Sept | 32.7 °C | 33 % | 36 km/h | 0.0 mm | Very high 45 |
| 24 Sept | 32.4 °C | 31 % | 29 km/h | 0.0 mm | High 38 |
| 25 Sept | 30.5 °C | 34 % | 23 km/h | 0.0 mm | High 28 |
| 26 Sept | 29.5 °C | 39 % | 28 km/h | 0.0 mm | High 32 |
| 27 Sept | 31.9 °C | 26 % | 28 km/h | 0.0 mm | Very high 41 |
| 28 Sept | 32.2 °C | 28 % | 31 km/h | 0.0 mm | Very high 39 |
| 29 Sept after | 33.1 °C | 25 % | 29 km/h | 0.0 mm | Very high 40 |
| 30 Sept after | 33.5 °C | 29 % | 20 km/h | 0.0 mm | High 36 |
| 1 Oct after | 33.2 °C | 32 % | 21 km/h | 0.0 mm | Very high 39 |
| 2 Oct after | 31.1 °C | 33 % | 31 km/h | 0.0 mm | High 38 |
| 3 Oct after | 33.4 °C | 31 % | 26 km/h | 0.0 mm | High 36 |
| 4 Oct after | 34.4 °C | 26 % | 23 km/h | 0.0 mm | High 38 |
| 5 Oct after | 34.9 °C | 23 % | 31 km/h | 0.0 mm | Very high 41 |
| 6 Oct after | 34.2 °C | 22 % | 40 km/h | 0.0 mm | Extreme 56 |
| 7 Oct after | 34.5 °C | 28 % | 34 km/h | 0.0 mm | Very high 50 |
| 8 Oct after | 34.1 °C | 27 % | 37 km/h | 0.0 mm | Very high 47 |
Its twins: fires that started in the same weather
It started with an FWI of 51.5, a minimum humidity of 18% and more than two months without rain. Fires in the area that started in weather like this since 2016: 16.
FWI at the start
51.5
Minimum humidity
18 %
Days without rain
60+
this fire
chosen twins
rest of the area
Almost identicalSimilar
Outlines of the closest twins
This fire · Unaí fire, 18 September 2021
4,238 ha
11 days
FWI 51.5
Min. humidity 18 %
Niquelândia fire, August 2025
8,504 ha
18 days
FWI 51.3
Min. humidity 19 %
209 km away, in 2025
First rain (1 mm or more) after it ended: 2.3 mm on 22 Sept.
Unaí fire, September 2024
5,606 ha
9 days
FWI 49.8
Min. humidity 21 %
23 km away, in 2024
First rain (1 mm or more) after it ended: 2.9 mm on 8 Oct.
Mimoso de Goiás fire, August 2025
4,174 ha
20 days
FWI 50.0
Min. humidity 19 %
181 km away, in 2025
First rain (1 mm or more) after it ended: 2.5 mm on 22 Sept.
Mimoso de Goiás fire, September 2019
8,410 ha
9 days
FWI 50.3
Min. humidity 17 %
213 km away, in 2019
First rain (1 mm or more) after it ended: 1.0 mm on 6 Oct.
Planaltina fire, September 2019
6,431 ha
7 days
FWI 48.7
Min. humidity 19 %
135 km away, in 2019
First rain (1 mm or more) after it ended: 1.0 mm on 27 Sept.
What happened to them
- 9 days
- median duration
- 5,021 ha
- median area
- 0 %
- went past 10,000 ha
- 2.3 mm
- rain at the end (median; 13 of 16 had it)
It burned an area similar to its twins (4,238 ha against a median of 5,021 ha) and lasted 11 days, against 9 days.
In 3 of 16, not even 1 mm fell in the ten days after the end: they went out without rain. In the rest, the first rainy day brought a median of 2.3 mm.
This is a bank of analogues: it shows what usually happens, not what will happen. With fewer than 15 twins we give no figures. How we calculate it
How it ended
—first rain
—no rain in ten days
36km/h · max. gust
It was considered over on 28 Sept, and not even 1 mm fell in the following ten days: it went out without rain. Twins with rain when they ended: 13 of 16, with a median of 2.3 mm.
Weather on this page: Open-Meteo.com (CC BY 4.0) · Copernicus Climate Change Service (ERA5)
How a twin is chosen
- Same area: fires that have already ended, less than 250 km from this one, since 2016.
- Same start: we compare the FWI on the first day, the minimum humidity that day and the run of days without rain before it. The slider sets how much they may differ.
- Only pages with final weather data (ERA5 reanalysis) calculated in the same way as this fire’s; agricultural and grass burns and pages with data under review are left out.
- Fires burning at the same time as this one (a week before or after) are left out: they share the same spell of weather and do not count as a precedent.
- They are sorted by similarity, and the outlines of the first five are drawn.
Before and after, from space
Drag the line to compare the same ground before the fire and after it.
↔
Before · 11 Sept 2021
After · 5 Oct 2021
Sentinel-2 did not pass over on that day. Try another date, or use false colour, which is daily.
If the day is cloudy, change the date: each satellite passes once a day. In false colour the burnt ground looks brown or red.
Detections table · 168Every satellite heat detection, one by one, with time, satellite, power and coordinates.
⬇ Download CSV
Times in UTC. Each detection is a 375 m pixel: a large fire yields hundreds per pass.
| Date and time | Satellite | FRP (MW) | Lat | Lon |
|---|
Other fires nearby
Frequently asked questions
- How long did the Unaí fire last?
- According to the heat detections seen by satellite inside the perimeter, it burned from 18 September 2021 to 28 September 2021 (11 days). The perimeter dates it from 18 September 2021 to 24 September 2021.
- How much area did it burn?
- The perimeter GWIS (Copernicus) rebuilt from heat detections is 4,238 hectares (42.4 km²). It is an estimate: official national figures may differ.
- Which municipalities burned?
- The fire only entered Unaí (4,262 ha, 0.5 %).
- What was the weather like?
- During the fire the temperature reached 36.7 °C, humidity dropped to 15 % and gusts hit 36 km/h. The fire danger index (FWI) reached 58, class Extreme.
- Where does this data come from?
- From the GWIS (Copernicus) burnt perimeter, NASA FIRMS VIIRS hotspots and the administrative boundaries of Brazil (geoBoundaries). It is not an official report.
- How did the fires that started in similar weather in this area end?
- Fires less than 250 km away that started since 2016 with a similar FWI, humidity and dry spell: 16. Their median duration was 9 days and their median area 5,021 ha; 0 % went past 10,000 ha. In 3 of 16, not even 1 mm fell in the ten days after the end: they went out without rain. In the rest, the first rainy day brought a median of 2.3 mm.
Where to verify it
A satellite detection is not an official report. Final figures and the fire’s status are published by each country’s emergency service.
Emergency number: 193 · Emergency number and official warnings
Satellite cross-check
History of this page · 1 Changes in area, dates, name, official record or merged pages, compared every night since 24 October 2026.
- Last day with fire: 24 September 2021 → 28 September 2021.
RSS Changes to this page With cross-checks and a citable version
Does something look wrong on this page?
This page is built from satellite data and official records, and it sometimes gets things wrong: the wrong dates, the wrong town, two fires merged into one, or something that was not a wildfire at all. If you know this fire first-hand (you live nearby, saw it, fought it or reported on it), tell us what really happened and we will check it.
Report an error
How we know this
- Perimeter: GWIS (Copernicus), rebuilt from heat detections rather than mapped on imagery.
- Dates adjusted with the VIIRS detections inside the perimeter, which said 18 September 2021 to 24 September 2021. 168 Suomi-NPP VIIRS detections on those dates.
- We have not matched this page with any official record.
- Weather: Copernicus ERA5 reanalysis at the fire location, in cells of about 25 km.
- Built-up area and population come from the JRC Global Human Settlement Layer (epoch 2020, 100 m cells), summed inside the perimeter: an estimate of what was there, not a damage count.
Where this data comes from
The perimeter comes from the Copernicus Global Wildfire Information System (GWIS), which rebuilds it from MODIS and VIIRS heat detections and publishes it under CC BY 4.0. It is not measured on imagery as in Europe, so it is an estimate. Heat detections come from the VIIRS sensors aboard Suomi-NPP and NOAA-20, distributed by NASA FIRMS at 375 m resolution. Municipal boundaries come from geoBoundaries ADM2 (Creative Commons Attribution 3.0 Intergovernmental Organisations (CC BY 3.0 IGO)). The area per municipality is computed by WorldFires by crossing the perimeter with those boundaries, so it may differ from each country’s official figure.