MERIT Hydro: Global Hydrography Datasets

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dem elevation flow-direction hand hydrography hydrosheds merit river-width upstream-drainage-area


MERIT Hydro is a new global flow direction map at 3 arc-second resolution (~90 m at the equator) derived from the version 1.0.3 of the MERIT DEM elevation data and water body datasets (G1WBM, GSWO and OpenStreetMap).

MERIT Hydro contains the output of a new algorithm that extracts river networks near-automatically by separating actual inland basins from noise caused by the errors in input elevation data. After a minimum amount of hand-editing, the constructed hydrography map shows good agreement with existing quality-controlled river network datasets in terms of flow accumulation area and river basin shape (see Figure 9a in the paper). The location of river streamlines was realistically aligned with existing satellite-based global river channel data (see Figure 10a in the paper). Relative error in the drainage area was smaller than 0.05 for 90% of GRDC gauges, confirming the accuracy of the delineated global river networks. Discrepancies in flow accumulation area were found mostly in arid river basins containing depressions that are occasionally connected at high water levels and thus resulting in uncertain watershed boundaries.

MERIT Hydro improves on existing global hydrography datasets in terms of spatial coverage (between 90N and 60S) and representation of small streams, mainly due to increased availability of high-quality baseline geospatial datasets.

You can use this web app to visualize MERIT Hydro data. The app's source code is available.

Known Problems:

  • River width (Update from GWD-LR v1): Width algorithm was updated to consider sub-pixel water fraction. Now, 30 m water map is used for width calculation at 90 m resolution. Currently river width is calculated for each channel separately in braided/anabranching sections. Merged river width should be calculated.
  • Water body map: There are some inconsistencies between the DEM land sea mask and wate body data (such as new islands along the coast). The quality of OpenStreeetMap water body layer is not uniform in all areas.
  • Channel bifurcations: Channel bifurcation is not well represented in the current version. Each pixel is assumed to have only one downstream direction. Secondary (or multiple) downstream direction should be considered, to represent complex river networks in the delta regions, floodplains, and braided rivers.
  • Underground rivers/tunnels: Major underground rivers/tunnels should be implemented to improve large-scale water balance.
  • River/lake separation: Rivers and lakes need to be separated better for some applications.
  • Below-sea-level areas: The areas below sea level in coastal regions are not well represented in adjusted elevation data.
  • Flow direction over glaciers: Flow direction over glaciers is not well represented, because the elevation of glacier centerline is higher than glacier edge.
  • Supplementary data: It would be better to add location of GRDC gauging stations, water falls, reservoirs, etc.

Data Sources:


92.77 meters


Name Units Description
elv m



Flow Direction (Local Drainage Direction)

  • 1: east
  • 2: southeast
  • 4: south
  • 8: southwest
  • 16: west
  • 32: northwest
  • 64: north
  • 128: northeast
  • 0: river mouth
  • -1: inland depression

River channel width at the channel centerlines. River channel width is calculated by the method described in [Yamazaki et al. 2012, WRR], with some improvements/changes on the algorithm.


Land and permanent water

  • 0: Land
  • 1: permanent water
upa km^2

Upstream drainage area (flow accumulation area)

upg Number of upstream pixels

Upstream drainage pixel (flow accumulation grid).

hnd m

Hydrologically adjusted elevations, also know as "hand" (height above the nearest drainage). The elevations are adjusted to satisfy the condition "downstream is not higher than its upstream" while minimizing the required modifications from the original DEM. The elevation above EGM96 geoid is represented in meters, and the vertical increment is set to 10cm. For detailed method, see [Yamazaki et al., 2012, WRR].


Visualization of the river channel width.

Terms of Use

Terms of Use

Citation to the paper is adequate if you simply use MERIT Hydro. If you asked for help for additional handling/editing of the dataset, or if your research outcome highly depends on the product, the developer would request co-authorship.

MERIT Hydro is licensed under a Creative Commons "CC-BY-NC 4.0" or Open Data Commons "Open Database License (ODbL 1.0)". With a dual license, you can choose an appropriate license for you.

To view a copy of these license, please visit:

  • CC-BY-NC 4.0 license: Non-Commercial Use with less restriction.
  • ODbL 1.0 license: Commectial Use is OK, but the derived data based on MERIT Hydro should be made publicly available under the same ODbL license. For example, if you create a flood hazard map using MERIT Hydro and you would like to provide a COMMERCIAL service based on that, you have to make the hazard map PUBLICLY AVAILABLE under OdBL license.

Note that the above license terms are applied to the "derived data" based on MERIT Hydro, while they are not applied to "produced work / artwork" created with MERIT Hydro (such as figures in a journal paper). The users may have a copyright of the artwork and may assign any license, when the produced work is not considered as "derived data".

By downloading and using the data the user agrees to the terms and conditions of the license. Notwithstanding this free license, we ask users to refrain from redistributing the data in whole in its original format on other websites without the explicit written permission from the authors.

The copyright of MERIT Hydro is held by the developers, 2019, all rights reserved.


  • Yamazaki D., D. Ikeshima, J. Sosa, P.D. Bates, G.H. Allen, T.M. Pavelsky. MERIT Hydro: A high-resolution global hydrography map based on latest topography datasets Water Resources Research, vol.55, pp.5053-5073, 2019, doi:10.1029/2019WR024873

Explore with Earth Engine

Code Editor (JavaScript)

var dataset = ee.Image('MERIT/Hydro/v1_0_1');

var visualization = {
  bands: ['viswth'],

Map.setCenter(90.301, 23.052, 10);

Map.addLayer(dataset, visualization, 'River width');
Open in Code Editor