A map of the land that flooded, the flooded area in square kilometres, and how many people live there, with a low and high figure. You also get a one-page PDF and the figures as a spreadsheet.

Which dates should I choose?

Choose a day on or just after the flood. The Sentinel-1 satellite passes most places every 6 to 12 days, so looking back 12 days usually catches at least one pass. We compare it with the driest month of a normal year, or with a month you choose.

Is the people figure the number affected?

It is the number of people who live where we saw water, from the GHSL 2025 population map. Use it to see where to look first and roughly how many people may need help.

What if my district is very big?

We map big districts with larger squares (20, 40, 80 or 160 metres). Districts more than about 277 km across are split into parts, and you choose one. For a whole large district or a series of dates, talk to us about your project.

Can I use the map in a situation report?

Yes. Keep the line "Generated at TechnicalGIS.com" and the data credits. Each answer has its own link and is kept for 90 days. In a major disaster, the Copernicus Emergency Management Service and UNOSAT produce checked flood maps for national authorities and UN agencies; use theirs where they exist.

Flood impact

Choose your district and a date, and we'll map the land that flooded and count how many people live there. Radar sees through cloud, so it works in the middle of the rains. You get a map, the numbers and a one-page sheet, usually in one to three minutes.

1. Choose your district

Country

2. Choose the dates

Up to Days to look back

We compare the latest radar image in these dates with a dry month, so only new water counts.

Compare with

Choose a country and a district first.

Usually ready in one to three minutes. Free, up to 15 new questions a day each; answers we've already worked out are instant and don't count. Privacy.

Choose a country to see its districts, then tap one to pick it.

District boundaries from geoBoundaries, simplified for the web.

Also try Season condition, or Farm check for one farm.

How it works

Radar. We take the latest Sentinel-1 radar images in your dates and compare them with images from a dry month, from the same satellite track where we can.
Water. Calm water shows up dark on radar. Land that has turned clearly darker since the dry month is marked as flooded.
New water only. Rivers, lakes and reservoirs that hold water most years (from the JRC Global Surface Water record) are taken out.
People. We add up the GHSL 2025 population map over the flooded land. A stricter and a looser water rule give the low and high figures.

Each answer ends with one line on how much weight it can bear. Radar misses water under thick forest, tall crops and between buildings, and it shows one moment, so a flood that came and went between passes may not appear.

We use only data whose licence allows anyone to reuse the results, and we credit every source with every answer. No personal or household data is used.

Data and credits

Licences checked on each provider's own page, last on 29 October 2026.

Source	Licence	Credit
Sentinel-1 radiometrically terrain corrected backscatter	CC BY 4.0	Contains modified Copernicus Sentinel-1 data, processed to RTC by Catalyst and provided by Microsoft Planetary Computer under CC BY 4.0.
JRC Global Surface Water occurrence	Free of charge, without restriction of use (Copernicus programme)	Source: EC JRC/Google. Pekel, J.-F. et al. (2016), Nature 540, 418–422. https://doi.org/10.1038/nature20584.
GHSL GHS-POP R2023A population grid (2025)	CC BY 4.0	European Commission, Joint Research Centre: GHS-POP R2023A. Pesaresi, M. et al. (2024), Int. J. Digital Earth 17(1). https://doi.org/10.1080/17538947.2024.2390454. CC BY 4.0. Resampled and summed over the flooded area by TechnicalGIS.
geoBoundaries administrative boundaries	Per country (CC BY, ODbL or open government licence)	Runfola, D. et al. (2020) geoBoundaries: A global database of political administrative boundaries. PLoS ONE 15(4): e0231866.

Questions

What will I get?: A map of the land that flooded, the flooded area in square kilometres, and how many people live there, with a low and high figure. You also get a one-page PDF and the figures as a spreadsheet.
Which dates should I choose?: Choose a day on or just after the flood. The Sentinel-1 satellite passes most places every 6 to 12 days, so looking back 12 days usually catches at least one pass. We compare it with the driest month of a normal year, or with a month you choose.
Is the people figure the number affected?: It is the number of people who live where we saw water, from the GHSL 2025 population map. Use it to see where to look first and roughly how many people may need help.
What if my district is very big?: We map big districts with larger squares (20, 40, 80 or 160 metres). Districts more than about 277 km across are split into parts, and you choose one. For a whole large district or a series of dates, talk to us about your project.
Can I use the map in a situation report?: Yes. Keep the line "Generated at TechnicalGIS.com" and the data credits. Each answer has its own link and is kept for 90 days. In a major disaster, the Copernicus Emergency Management Service and UNOSAT produce checked flood maps for national authorities and UN agencies; use theirs where they exist.

See two worked examples, read what we're for, or talk to us about your project. For major disasters, see the checked maps from Copernicus EMS and UNOSAT.