Watch where the rain goes, on any place in Tamil Nadu
Tap your land and watch the next three days of forecast rain, or a storm you choose, fall on a 3D satellite map, run downhill and gather in the low ground. Then read which roads go under, the worst hour, and how deep the water gets at your plot and when it drains.
Free. Sign in once with your phone to run it.
- Rain that falls through a real storm curve and runs downhill by the physics of shallow water
- Which named roads take more than a foot of water, and for how far
- The depth at your pin hour by hour, when it peaks and when it drains
- Full screen, a timeline you can scrub, and heights stretched to see the ground
Freeevery run
What the simulation does
Rain water that collects on low ground faster than it can drain away, flooding streets and plots until it runs off or soaks in.
- The ground
- 30 m
Heights from a satellite radar survey of the whole state, read every 30 metres over a 6.6 km box around your pin.
- The water
- Real physics
Rain falls through a storm that builds, peaks and eases, then runs downhill, speeds up on slopes, fills dips and spills on, by the physics of shallow water.
- The roads and your pin
- Over a foot
A road counts as under water where more than 30 cm stands on it in a real pool; bridges, flyovers and tunnels are left out. Your pin gets its depth hour by hour, when it peaks and when it drains.
How to see where rain floods near a plot
- 1
Pick the place
Sign in with your phone, then type a place name, tap your land on the map, paste a Google Maps link, or use your location.
- 2
Pick the rain
The forecast for the next three days, or a storm: heavy, very heavy or extremely heavy, over 3, 12 or 24 hours.
- 3
Let it rain
Watch the storm, then scrub the timeline, tap any spot for its depth, or go full screen.
When it helps with land
Before buying a plot
See whether the land sits in the low ground the water runs to, and how deep it could get.
Choosing a street
Compare the roads around a house you are looking at: which go under first and which stay dry.
Planning a building
Decide how high to raise the plinth and where the water will try to run on your site.
This shows where rain goes on the shape of the ground when the drains cannot keep up. It does not know about drains, canals, lake releases, the tide or how much the soil soaks up, and the satellite survey reads rooftops and trees as ground. Use it to understand the land, and check the mapped flood zone and the water bodies for the plot before you rely on it.
Questions people ask
Is this a flood forecast?
No. It shows where a given amount of rain goes on the shape of the ground when the drains cannot keep up. Real flooding also depends on drains, canals, lake releases and the tide, which it does not model.
Where do the ground heights come from?
From the Copernicus 30 m surface model, a satellite radar survey of the whole earth. It reads rooftops and tree canopy as ground, so a street between tall buildings can look like a channel.
How big an area does it cover?
A box about 6.6 km across around your pin. Rain that would run in from outside the box is not counted, and water that reaches the edge runs out of it.
Why do lakes start full?
Late in a wet monsoon the lakes and tanks are full, so new rain spills over them instead of being stored. Starting them full shows that worst case. A pin on a lake says so.
What do heavy, very heavy and extremely heavy mean?
They are the India Meteorological Department's bands for a day of rain: heavy is 64.5 to 115.5 mm, very heavy 115.6 to 204.4 mm, extremely heavy 204.5 mm or more. You pick whether it falls over 3, 12 or 24 hours.
When does a road count as under water?
When more than 30 cm, about a foot, stands on it in a pool of at least about 0.7 hectares. Smaller puddles are mostly survey noise. Bridges, flyovers and tunnels are left out.
Does it cover all of Tamil Nadu?
Yes, every place on land in the state. A pin outside Tamil Nadu or out at sea says so.
Where does the forecast come from?
From MET Norway, whose global weather model gives the rain for any place hour by hour for about two and a half days and in six hour steps after that. The mini lets the next three days of it fall on your place. A forecast can be wrong, so read it as one likely outcome.
Does it use my location?
Only if your browser already allows this site to see it, or when you press the location button. The map then opens on your spot. When you are signed in, the last location your browser gave is saved to your account so maps can open there next time; a place you tap or a link you paste is never saved.
What does Count working drains do?
It lets drains take away 20 mm of water an hour wherever water stands on land, the low end of what Greater Chennai Corporation gives for its existing drains (new drains are built for 68 mm an hour). Off, the default, shows the worst case: drains blocked or overwhelmed.
Is it free?
Yes. Sign in once with your phone number and run it as often as you like. Before you sign in, the map plays a demo storm on Pallikaranai.