FullBasin on MERIT Hydro · 90 m

The three tiers

What is in the release

Tier 1Where does a pixel drain to?

Delineating a basin means recovering the complete catchment that drains to an outlet: every upstream pixel, bounded by the drainage divide. Tier 1 does this for the whole land surface at once. The basin-ID raster covers every land pixel, and the attribute table holds one row for each of the 24,587,290 outlets, from the Amazon down to single coastal pixels. 340,991 of these outlets have a drainage area of at least 1 km²; they are the basins of this release and together cover more than 99.5% of the land. Raster and table share one addressing rule: basin_id = table_index + 1. Going from a pixel to its record is therefore an array offset: no join, no dictionary, no lookup table.

Tier 2What drains into a pixel?

Each pixel stores a depth-first interval. Whether one pixel lies upstream of another is then a single interval-containment comparison, independent of the size of the catchment, though listing the pixels the test returns still takes time in proportion to their number. The index is derived from the D8 network and carries its terms: dfs_in and dfs_out are released under MERIT Hydro’s ODbL 1.0 terms. The MERIT Hydro layers themselves are not redistributed.

Tier 3What is upstream of a pixel like?

Tier 3 provides sixteen upstream attributes — eight terrain statistics and eight basin-shape metrics — for every pixel with at least 10 km² of upstream drainage area. Each shape metric needs that pixel’s own catchment divide, which is why attributes like these are normally published for a fixed list of basins. Tier 2 makes the divide fall out of two stored numbers, and that is what makes doing it at every pixel affordable.

Layer forms

The basin layers come in two forms: bsn, the 90 m raster in which every land pixel carries the ID of its basin; and bnd, the boundaries of those basins as simplified vector lines, on this site now and in the next Zenodo archive. The upstream index and the sixteen attributes are 90 m rasters. The MERIT Hydro layers underneath are not redistributed; they come from the MERIT Hydro team under their own terms.

Walk-through

A recorded walk-through

A recorded talk on YouTube, covering how the three tiers are built and what each one is for. The talk plays here in the page; nothing loads from YouTube until you press play.

A note on the narration: the talk is Lulu Jiang’s throughout, but the voice you hear is synthetic, made with MiniMax. If you speak English well and would like to volunteer to record it, we would welcome that. Please write to lulu_jiang@pku.edu.cn. The content will not change when the voice does.

Cost and validation

What it cost to build, and how it was checked

Fine-resolution hydrography underpins flood prediction, large-sample hydrology and machine-learning streamflow models. Computing basin identity, upstream topology and morphometry together at pixel resolution is hard because of scale and connectivity at once: computing per-pixel attributes across a 75.17-billion-pixel grid, 22.26 billion of them land, exceeds the memory of standard GIS software, and the naive fix — tiling — breaks the very basins being measured.

The complete pipeline ran in about 21 hours on one 13-thread node with terabyte-scale memory. It processed regions that keep every basin whole, so no drainage basin is cut across an arbitrary raster tile. Each tier was checked on its own terms:

Tier	What was checked	Against what
1 · basin masks	the pixel count of every basin	exact agreement with the flow-accumulation raster
2 · upstream index	the interval index checked pixel by pixel against the D8 network it was built from	consistent for every pixel
3 · attributes	catchment perimeter, the most error-sensitive of the sixteen, on about 150,000 upstream-catchment masks	three independent perimeter implementations

Perimeter is the one benchmarked because a single misplaced boundary pixel changes it by about 4/P, while it changes the area by about 1/A, where A and P are the pixel counts of the catchment and its boundary. The manuscript gives the full validation.

Download version 1.0 100 files, 142.2 GB · licence by layer · 10.5281/zenodo.20344113. The version 1.1 archive is being prepared. Until it is out, start from the basin and region mask.

Before you fetch 142 GB: every layer and column is defined in the glossary, the file list and the per-region sizes are in the Zenodo record, and the walk-through above runs the three questions on one real basin.

The manuscript is in open discussion at Earth System Science Data; the discussion paper is open for comment there.