Reservoir water intelligence
The level of every reservoir we can see, with its age.
Satellite altimetry, filtered by a frozen specification, judged without a gauge, and published with its error budget. Every number carries how old it is, how it was made and how wrong it can be.
The catalogue, the method and the licence register are open to anyone. Levels, series and forecasts need an api key.
- Kept observation, and the newest is the observed level
- Discarded by the filter, and still shown
- Carried forward to today
- Forecast, with its 80 percent band
A schematic. It carries no measurement and describes no reservoir.
Coverage
- Registered
35,295
reservoirs in the Global Dam Watch registry
- Observable
31,112
geometrically observable by SWOT, holding 99.5% of registered capacity
- Usable
27,641
with a filtered series good enough to report a level
What a record holds
Three values, each with its own provenance
A level shown without its age is wrong by construction, because the displayed value's age is the current value's error. So every value here travels with the fields that make it readable.
01
Observed
The newest kept observation
Carries its observation time, its age at display, its status, and an 80 percent band.
02
Estimated
The observed value advanced to today
Carries its method, which is carry-forward, and its age.
03
Forecast
The level three to four weeks ahead
Carries its eligibility, its origin, and quantiles at each lead.
What is not published elsewhere
The judgment layer is the part that is hard to reproduce
Every input this product reads is free. Coverage is reproducible in weeks by anyone, so coverage is not the claim. These three were checked against eight free products and one commercial competitor.
A per-reservoir error budget
Free products publish a per-observation uncertainty and one pooled validation figure. None publishes a budget stratified by climate, size and latitude, or a calibrated probability that a series meets a stated accuracy rule.
A calibrated forecast
A forecast on a reservoir level series, with an 80 percent band and the coverage that band was measured to hold, was not found anywhere.
Validation below 1 km²
Nadir altimetry validates at large lakes. The held-out set here spans the size classes and reports the pass rate by class, 0.53 under 1 km² against 0.75 above 100 km².
Survey of 7 September 2026. One clause that failed is recorded with the others: a filtered, validated elevation series is published elsewhere, at 243 lakes.
Measured, not asserted
Accuracy and freshness, as figures
Uncertainty is a range here rather than an adjective, and the awkward half of each claim travels with the flattering half.
- 65 of 95
- held-out reservoirs meet 0.5 m RMSE, across four Köppen climate classes and six countries
- 0.16 m
- median RMSE against gauges at the satellite passes
- 4.06 days
- median from satellite pass to published level, 5.06 days at the 90th percentile
- 14 days
- median age of the newest displayed value on a random day
- 15 days
- median interval between kept observations at the median usable reservoir
- 13%
- of reservoir-days where the newest value is more than 30 days old
- 178
- gauge-judged reservoirs in the label registry, re-scored every month
- nine
- countries the validation rests on, with nothing yet in Africa, China or Southeast Asia
If the mission ends
No number here rests on one spacecraft
SWOT is past its nominal life and its only wide-swath successor is planned for 2034. Every usable reservoir carries what it would keep without it, measured on published ground tracks rather than assumed.
- 1,155
- reservoirs at or above 20 km² keep a level from a Sentinel-3 or Sentinel-6 track, holding 81.1% of usable capacity
- 2,600
- reservoirs have a nadir track crossing them, holding 84.2% of usable capacity
What this does not claim
The limits, stated first
These are in the product definition rather than in a footnote, because an auditor who finds a limit you did not mention discounts the page it was missing from.
Not real time
No height sensor passes over a reservoir daily. Every level carries its age, and the age is the error.
Not a gauge replacement where a gauge exists
A gauge is a centimetre daily against the satellite’s 15 cm every two weeks. Where an operator publishes, the value here is independence and audit rather than precision.
Not validated everywhere
A reservoir in a country with no public truth gets a transferred error budget, never a validated one, and its record says which.
Silent where it should be
Below its published trust floor the product states no level and says so, keeping the row, the trust figure and the reason. An absent level is never drawn as zero.
Start with one reservoir and one day.
The catalogue is open. Every row links to a record that shows what the product knows, what it does not, and where each figure came from.