San Alejo fire, March 2017 San Alejo
The fire started on 4 March 2017 in San Alejo, El Salvador, and satellites saw it burning for 10 days. Copernicus’s global GWIS system rebuilt a burnt perimeter of 1,073 hectares from heat detections, spread across a single municipality.
It is the 16th largest in Departamento de La Unión since 2016 (of 16 with a page). Number 12 in El Salvador in 2017, of 17.
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- Burnt area
- 1,073ha
- GWIS perimeter (Copernicus)
- Duration
- 10days
- 4 Mar 2017 – 13 Mar 2017
- Municipalities hit
- 1
- municipalities
- Started on
- 4 Mar
- 2017
- Heat detections
- 53
- in a single hotspot: 40 MW
- Danger at start
- 51
- Extreme · FWI index
- Average daily power
- 63MW
- detected power per day, on average
Where it burned
How it evolved, day by day
Fire radiative power detected each day, in megawatts, and number of hotspots. The magenta bar marks the peak day.
The weather it burned in
It had gone more than two months without rain (1 mm or more) when it started. Rain came after the fire: 10.8 mm on 14 Mar.
This area had burned before
No earlier perimeters overlap this fire since 2016, when the satellite record begins.
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
-
San Alejo where it started1,079 ha reached on 4 Mar4.6 %
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 2015Inside the perimeter there were about 0.90 hectares of built-up land and about 60 residents (GHSL 2015, 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)
| Day | High | Min. humidity | Peak gust | Rain | Danger (FWI) |
|---|---|---|---|---|---|
| 4 Mar | 37.4 °C | 21 % | 56 km/h | 0.0 mm | Extreme 51 |
| 5 Mar | 38.6 °C | 14 % | 47 km/h | 0.0 mm | Extreme 54 |
| 6 Mar | 38.5 °C | 21 % | 40 km/h | 0.0 mm | Extreme 50 |
| 7 Mar | 38.9 °C | 25 % | 42 km/h | 0.0 mm | Very high 49 |
| 8 Mar | 37.6 °C | 25 % | 50 km/h | 0.0 mm | Extreme 56 |
| 9 Mar | 37.0 °C | 27 % | 45 km/h | 0.0 mm | Very high 48 |
| 10 Mar | 36.5 °C | 31 % | 38 km/h | 0.0 mm | Very high 41 |
| 11 Mar | 37.5 °C | 23 % | 35 km/h | 0.0 mm | Very high 41 |
| 12 Mar | 38.2 °C | 27 % | 31 km/h | 0.0 mm | Very high 39 |
| 13 Mar | 37.1 °C | 34 % | 30 km/h | 0.0 mm | High 38 |
| 14 Mar after | 37.6 °C | 29 % | 37 km/h | 10.8 mm | Low 7 |
Before and after, from space
Drag the line to compare the same ground before the fire and after it.
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 · 53Every satellite heat detection, one by one, with time, satellite, power and coordinates.
| Date and time | Satellite | FRP (MW) | Lat | Lon |
|---|
Other fires nearby
- 2,269 haConchagua3 March 2017 · 10 days · 15 km away
- 4,821 haIntipucaMarch 2019 · 19 days · 23 km away
- 2,101 haNullFebruary 2026 · 19 days · 23 km away
- 2,866 haIntipucaMarch 2026 · 12 days · 24 km away
- 4,087 haIntipuca17 March 2017 · 11 days · 27 km away
- 2,097 haSan MiguelMarch 2026 · 15 days · 30 km away
Frequently asked questions
- How long did the San Alejo fire last?
- According to the heat detections seen by satellite inside the perimeter, it burned from 4 March 2017 to 13 March 2017 (10 days). The perimeter dates it from 4 March 2017 to 11 March 2017.
- How much area did it burn?
- The perimeter GWIS (Copernicus) rebuilt from heat detections is 1,073 hectares (10.7 km²). It is an estimate: official national figures may differ.
- Which municipalities burned?
- The fire only entered San Alejo (1,079 ha, 4.6 %).
- What was the weather like?
- During the fire the temperature reached 38.9 °C, humidity dropped to 14 % and gusts hit 56 km/h. The fire danger index (FWI) reached 56, class Extreme.
- Where does this data come from?
- From the GWIS (Copernicus) burnt perimeter, NASA FIRMS VIIRS hotspots and the administrative boundaries of El Salvador (geoBoundaries). It is not an official report.
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: 911 · Emergency number and official warnings ›
Satellite cross-check
History of this page Changes in area, dates, name, official record or merged pages, compared every night since 24 October 2026.
No changes since 24 October 2026.
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.
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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 4 March 2017 to 11 March 2017. 53 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 2015, 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 (Public Domain). 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.