Watershed

Rewrite the Earth's water and time, then see whether people could live and travel there.

An educational sandbox for real terrain. Draw an area anywhere on Earth, pick a storm, and watch real elevation data fill its valleys, carve rivers and run to the sea. Then drain the oceans back to the Ice Age, roll the atlas back to the Bronze Age, and send a caravan across what remains.

Get Watershed on itch.io → Will it run on my PC?

Version 0.2.4Windows 10 / 11 · 64-bitAbout 25 MBNo account, no telemetry

Rain shafts and cloud shadows over Alpine terrain, water gathering in the valleys — A desert cloudburst dropped on the Alps: 60 mm/h. Torrents in every valley, and the ground stays readable under the storm.

Weather

Rain that has to go somewhere.

Six storm presets with their real order of magnitude, from a desert cloudburst to a monsoon week, or set every number yourself. A GPU shallow-water solver runs the physics live: water races down steep faces, ponds in basins, drains to real sinks, and recedes after the rain stops through infiltration and evaporation.

Cloud shadows, rain and lightning play over the terrain, and you can switch them off.
A quiet procedural soundscape follows the millimetres and, as you zoom in, the speed of the rivers. Off by default.
Pause at any moment and probe depth and flow at any point.

The floor of the Persian Gulf exposed with the sea lowered by 500 metres — The Persian Gulf drained to −500 m: a valley where the sea is today, the Strait of Hormuz still water.

Ocean

Move the sea.

Lower or raise the world's sea level from −500 m to +80 m on real bathymetry. The Gulf drains into a river valley, Dover joins Calais, deltas drown. Presets for today, the last Ice Age at −120 m, and a world with no ice at all, or type the exact metre you want.

A walking route from Dover to Calais across the dry Channel floor at Ice Age sea level — Dover to Calais on foot, 49 km of land bridge at the Ice Age sea level.

Time

Roll the atlas back.

A year slider from 3000 BC to today: historical city names, ancient peoples, trade routes and empire borders. Discoveries shows every mapped historic site in view, plus curated atlases of Arabian stone monuments and world rock art. Era scenes set the sea level, the year and a matching storm in one click.

At the Ice Age sea level a camel caravan crosses from Arabia to Egypt over the Strait of Tiran and the dry Gulf of Suez — Ice Age, −120 m: the caravan crosses from Arabia to Egypt over Tiran and the dry Gulf of Suez, camps marked each night.

Journey

Send a caravan across what remains.

Place two flags, choose a camel or an ox, a party and a cargo. The route threads the valleys, walks around lakes and the sea, crosses rivers only where it must, and hops between the oases, wells and cities of the chosen year. Watch the caravan travel day by day, with camps, fords, thirst warnings and a survivability verdict. Lower the sea and it takes the land bridge.

Share links reproduce an entire scenario for someone else, storm, sea, year and journey included.

Era scenes

One click, one world.

Scene	Sea level	Atlas year	Suggested storm
Today	0 m	2026	none, you choose
Last Ice Age	−120 m	20 000 BC	Steady soaking rain, 12 mm/h for 24 h
Green Arabia	−10 m	7000 BC	Wet season, 10 mm/h for four weeks
Bronze Age	0 m	1500 BC	Monsoon week, 30 mm/h for seven days
Roman world	0 m	AD 100	none, you choose
No ice left	+70 m	2026	none, you choose

Requirements

What it needs.

Windows 10 or 11, 64-bit.
A graphics card or laptop chip with WebGPU support. Any card from the last six years or so. The app locks the highest detail on small chips and lets you unlock it at your own risk.
An internet connection for map and terrain data. Areas you revisit are cached on disk.
About 25 MB of disk space plus the terrain cache.

Honesty

What it isn't.

Every layer is real data with its source shown. Every number has a reason. Nothing is a calibrated engineering model, and the app says so. Do not use it to decide whether your house will flood.

Windows may show "Windows protected your PC" on first run because the installer is not yet code-signed. Choose More info, then Run anyway. The app installs per user and needs no administrator rights.