MERIT-Plus Dataset: Delineation of endorheic basins in 5 and 15 min upscaled river networks
Description
The MERIT-Plus river network datasets in 5 and 15 arc minute resolution add value to the original upscaled IHU MERIT data with the main purpose of this work to identify the endorheic and exorheic basin types that are missing in the source datasets. Merging (cleanup) of small endorheic basins introduced few local changes in flow direction and basin identification data but made the datasets more suitable for a broader range of hydrological modeling applications that simulate water balance and accumulation in the endorheic lakes or land depressions.
Abstract
Endorheic drainage basins, those inland basins not connected directly to ocean, are essential for hydrological modeling of global and regional water balances, land surface water storage, gravity anomalies, sea level rise, etc. Within many hydrological model frameworks, river basins are defined by digital river networks through their flow direction and connectivity datasets. Here we present an improvement to gridded flow direction data and its derivatives produced from upscaled global 5 and 15 arc minute MERIT networks. We explicitly label endorheic and exorheic drainage basins and alter the delineation of endorheic basins by merging small inland watersheds to the adjacent host basins. The resulting datasets have a significantly reduced number of endorheic basins while preserving the total land portion of those basins since most of the merged catchments were inside other larger endorheic areas. We developed and present here the endorheic basin delineation method. This method performs an analysis of the contributing river and basin geometry relative to the location of the flow end point (i.e. potential endorheic lake), proximity of the latter to the drainage basin boundary and the elevation difference between the basin's lowest point and potential spillover location at the basin boundary. The new digital river network was validated using the University of New Hampshire Water Balance Model by comparing the water balance of endorheic inland depressions with modeled accumulation of water in their inland lakes based on the observed historical climate drivers used by WBM.
Methods
Description of methods used for collection/generation of data:
We used the endorheic basin delineation method that we have developed specifically to address the issue of erroneous basins. This method performs an analysis of the contributing river and basin geometry relative to the location of the flow end point (i.e. potential endorheic lake), proximity of the latter to the drainage basin boundary and the elevation difference between the basin's lowest point and potential spillover location at the basin boundary.
Erroneous coastal endorheic basins are re-connected to the ocean directly through fjord-like passages found from high resolution (30 m) coastline vector dataset (OpenStreetMap, 2022) or merged as a tributary to a larger river running to the ocean.
Methods for processing the data:
The following source data processing steps are used:
1. Create initial list of all mouth outlets and assign first classification:
This is done by filtering out all outlets and checking them for the absence of nodata values in the adjacent grid cells. This results in a list of exorheic mouth points, and the list of potentially endorheic outlets to be further processed in the next steps.
2. Coastal segmentation of mouth outlet clusters:
Both the original 3 arc second MERIT network (Yamazaki et al., 2019) and the set of upscaled MERIT river network datasets (Eilander et al., 2021) allow a grid cell to have a flow direction value. Entirely fresh water grid cells in the estuary of large rivers, such as the Amazon, also have zero values for the flow direction making it potentially endorheic in Step 1. However, these "mouth" grid cells do not accumulate water over time as endorheic lakes and, therefore, cannot be included as endorheic basins. In this step we change the classification of these false endorheic outlets by checking whether these are adjacent to a coastal exorheic outlet grid cell or can be connected to it through the chain of other such false outlets. If a potentially endorheic outlet (all cells adjacent have no nodata values) can be connected to the coast through a continuous chain of other exorheic outlets, then it is identified as exorheic. The rationale of this step is checking adjacency and/or chain adjacency conditions which does not require the use of any additional dataset, such as high resolution ocean coastline vector or ocean high resolution grid mask, making this step self-sufficient and solely based on the flow direction source data itself.
3. Use ocean or land mask:
In this step, we apply a high resolution vector or grid land mask to check whether the mouth outlet grid cell has an ocean on its sub-cell level or located at a minimal distance from the ocean. The minimal distance is an input parameter with default value set to zero which means no checking by distance. This step is optional because it involves the use of an additional high resolution land mask dataset which may not be available to the user. In this work we used land vector polygons at 30 m segments from OpenStreetMap (OpenStreetMap, 2022).
- 4. Merging of small inland endorheic drainage basins to neighboring drainage basins:
Because endorheic basins are partly defined by the ambient climate so that the water balance and potential endorheic lake accumulation does not spill over the low "pour points". Those that are currently endorheic could reconnect to a larger adjoining basin. Thus, small size (e.g. up to 100 km2) endorheic basins inside a larger basin requires further assessment, especially if its mouth point is located at its own basin boundary. The location of an outlet point at its own basin boundary of a small endorheic basin can be the result of unresolved connectivity through a narrow canyon-like passage that is not reflected in the source DEM dataset used to produce the river flow data. We therefore implemented a routine to identify those small basins and to reconnect them to their larger adjacent basins by the analysis of the contributing river and basin geometry relative to the location of the flow end point (i.e. potential endorheic lake), proximity of the latter to the drainage basin boundary and the elevation difference between the basin's lowest point and potential spillover location at the basin boundary.
The multi-option approach is implemented in the sequence of the following actions while processing each endorheic basin:
1) Filter out all endorheic basins by maximum drainage basin area size parameter. This is the most essential filter since we target for merging only small basins such that their removal will not significantly change the total global area of endorheic land. Most of those small basins merge into a host basin which is itself endorheic. These cases do not change the total endorheic area.
2) Locate all inside and outside basin boundary grid cells and record elevation of each. The MERIT dataset comes with the minimum river surface elevation in a grid cell which we use here and refer as "elevation".
- 3) For each inside boundary cell trace the flow path to the basin outlet cell, record it and its flow path length.
- 4) Identify and mark the pour point grid cell on the inside boundary by the lowest elevation or minimum flow path length criteria.
- 5) Check whether the difference in elevation between the pour point and outlet cell or the flow path length is equal to or less than the corresponding "Maximum flow path length" input parameter value. Skip this basin or continue to the next action items based on the elevation difference condition.
- 6) Trace the flow path from the pour point cell to the outlet and reverse the flow direction.
- 7) Connect the endorheic basin to the adjacent watershed using the lowest elevation or highest catchment area respectively in the outside boundary cells that are directly adjacent to the pour point. This is done by setting the flow direction on the pour point grid cell toward a cell in one of the adjacent basin's cells that meet the chosen criteria.
- 8) Set all basin ID grid cells of the merged watershed to the basin ID of the host watershed it is merged to.
Software-specific information needed to interpret the data:
All grid based water routing hydrological models are presently using byte (8-bit) encoding of river streamflow network that accepts multiple grid cell inflow and only one outflow direction.
Quality-assurance procedures performed on the data:
The new digital river network was validated using the University of New Hampshire Water Balance Model (WBM; Grogan et al., 2022) by comparing the water balance of endorheic inland depressions with modeled accumulation of water in their inland lakes based on the observed historical climate drivers used by WBM. The criteria was whether any given endorheic basin is likely to fill and overflow or will evapotranspiration rates exceed water accumulation rates and the basin remains hydrologically disconnected at the surface. The model was driven using MERRA2 historical climate drivers with a "pristine" land environment, i.e. all human components of the hydrological cycle were turned off (similar to the method employed by Karesdotter et al., 2022). WBM calculated endorheic lake water storage change using the difference between water inflow and evaporation from the lake surface where the latter is a function of storage and the lake geometry and bathymetry. If the lake storage and size exceeds the depression capacity then it is flagged as a false endorheic basin under historical (past 40 years) climate conditions. Checking all endorheic basins by this criteria we found only 12 (5 arc minute data) and 2 (15 arc minute data) such outliers before merging and after merging none were found.
We also checked the total/global endorheic land area and its location throughout the global land surface. Their endorheic basin land fraction (18.8 and 17.6 % for 5 and 15 arc minute resolution respectively), location and distribution match well with data from other sources (Vorosmarty et al., 2000; Wikipedia, 2022), and are almost identical to those from the source IHU MERIT data (Eilander et al., 2021).
Technical info
DATA & FILE OVERVIEW
File List:
Two zip files are provided for download, MERIT_plus_05min_v1.zip and MERIT_plus_15min_v1.zip The files are grouped by resolution. Each zip file contains 12 data files and one ReadMe file.
05 Arc Minute Data (MERIT_plus_05min_v1.zip)
1. MERIT_plus_05min_v1_flwdir.asc - Flow direction - Arc/Info ASCII Grid
2. MERIT_plus_05min_v1_flwdir.tif - Flow direction - GeoTIFF
3. MERIT_plus_05min_v1_IDs.asc - Basin IDs - Arc/Info ASCII Grid
4. MERIT_plus_05min_v1_IDs.tif - Basin IDs - GeoTIFF
5. MERIT_plus_05min_v1_IDs.csv - Basin attributes - Tab delimited text spreadsheet
6. MERIT_plus_05min_v1_IDsEnR.asc - Endorheic basin IDs only - Arc/Info ASCII Grid
7. MERIT_plus_05min_v1_IDsEnR.tif - Endorheic basin IDs only - GeoTIFF
8. MERIT_plus_05min_v1_IDsEnR.csv - Endorheic basin attributes - Tab delimited text spreadsheet
9. MERIT_plus_05min_v1_flwdirEnR.asc - Flow direction w/ EnR flag - Arc/Info ASCII Grid
10. MERIT_plus_05min_v1_flwdirEnR.tif - Flow direction w/ EnR flag - GeoTIFF
11. MERIT_plus_05min_v1_upstrArea.asc - Upstream area, km2 - Arc/Info ASCII Grid
12. MERIT_plus_05min_v1_upstrArea.tif - Upstream area, km2 - GeoTIFF
13. Readme_MERIT_plus_05min_v1.txt - List of files and notes - Plain Text
15 Arc Minute Data (MERIT_plus_15min_v1.zip)
1. MERIT_plus_15min_v1_flwdir.asc - Flow direction - Arc/Info ASCII Grid
2. MERIT_plus_15min_v1_flwdir.tif - Flow direction - GeoTIFF
3. MERIT_plus_15min_v1_IDs.asc - Basin IDs - Arc/Info ASCII Grid
4. MERIT_plus_15min_v1_IDs.tif - Basin IDs - GeoTIFF
5. MERIT_plus_15min_v1_IDs.csv - Basin attributes - Tab delimited text spreadsheet
6. MERIT_plus_15min_v1_IDsEnR.asc - Endorheic basin IDs only - Arc/Info ASCII Grid
7. MERIT_plus_15min_v1_IDsEnR.tif - Endorheic basin IDs only - GeoTIFF
8. MERIT_plus_15min_v1_IDsEnR.csv - Endorheic basin attributes - Tab delimited text spreadsheet
9. MERIT_plus_15min_v1_flwdir.asc - Flow direction w/ EnR flag - Arc/Info ASCII Grid
10. MERIT_plus_15min_v1_flwdir.tif - Flow direction w/ EnR flag - GeoTIFF
11. MERIT_plus_15min_v1_upstrArea.asc - Upstream area, km2 - Arc/Info ASCII Grid
12. MERIT_plus_15min_v1_upstrArea.tif - Upstream area, km2 - GeoTIFF
13. Readme_MERIT_plus_15min_v1.txt - List of files and notes - Plain Text
Notes:
- 1. These files were created by the UNH team
- 2. Original flow direction data source is from Eilander et al. (2021) and Yamazaki et al. (2019).
- 3. Changes to the original data include:
-
- a. Classification of all basins to endorheic (internal) and exorheic (flowing to the ocean) type using the following criteria:
Basin outlet point is not next to a nodata (ocean) grid cell except: -
- i. It is adjacent to another exorheic mouth point. This is done using a segmentation by 8-component labeling routine*.
- ii. It is on or within 25 km distance from high resolution (30 meter) land mask dataset (e.g. connected to the ocean by a narrow fjord-like passage).
- b. Elimination of small endorheic drainage basins by merging into a larger adjacent basin (applies only to those classified as endorheic basins in the source river network).
- c. Basin catchment area is less than 2500 km2 or 3000 km2 for 5 and 15 arc minute resolution grids. This is approximately 5x5 grid cells in the case of the 5 arc minute resolution data.
- d. Basin outlet/mouth point is at the boundary of the basin.
- a. Classification of all basins to endorheic (internal) and exorheic (flowing to the ocean) type using the following criteria:
Merging is done by changing flow direction of the mouth grid cell to the adjacent grid cell of the outside basin with the lowest elevation.
- 4. Projection is EPSG:3426
- Spatial resolution is 5 and 15 arc minutes.
*https://metacpan.org/pod/PDL::Image2D#cc8compt
Data records
MERIT-Plus v1 05 minute Data
File format: geotiff (.tif) and arc ascii (.asc)
File naming convention: MERIT_plus_05min_flwdir_v1_{Variable}.tif and MERIT_plus_05min_flwdir_v1_{Variable}.asc
Where {Variable} is one of: IDs, IDsEnR, flwdir, flwdirEnR or upstrArea.
Date Produced: Dec 2022.
Spatial Metadata:
Extent: X: −180 to +180
Extent Y: −60 to +85 Resolution: 0.083333 decimal degrees (5 minutes)
Coordinate reference system: longitude/latitude reference system: longitude/latitude /latitude (WGS84 datum)
Projection in PROJ.4 notation: "+proj = longlat + datum = WGS84"rows and columns: 1740, 4320
Units:
IDs: None
IDsEnR: None
flwdir: None
flwdirEnR: None
upstrArea: km2
No data value: Oceans, open-water, and Antarctica in the geotiff and ascii files have the no-data value of −9999. Exception, MERIT_plus_05min_v1_flwdir.tif has nodata value of 247.
File format: tab delimited (.csv)
File naming convention: MERIT_plus_05min_flwdir_v1_{Variable}.csv
Where {Variable} is one of: IDs or IDsEnR
Units:
IDs: None
IDsEnR: None
MERIT-Plus v1 15 minute Data
File format: geotiff (.tif) and arc ascii (.asc)
File naming convention: MERIT_plus_05min_flwdir_v1_{Variable}.tif and MERIT_plus_05min_flwdir_v1_{Variable}.asc
Where {Variable} is one of: IDs, IDsEnR, flwdir, flwdirEnR or upstrArea.
Date Produced: Dec 2022.
Spatial Metadata:
Extent: X: −180 to +180
Extent Y: −60 to +85 Resolution: 0.25 decimal degrees (15 minutes)
Coordinate reference system: longitude/latitude reference system: longitude/latitude /latitude (WGS84 datum)
Projection in PROJ.4 notation: "+proj = longlat + datum = WGS84"
rows and columns: 580, 1440
Units:
IDs: None
IDsEnR: None
flwdir: None
flwdirEnR: None
upstrArea: km2
No data value: Oceans, open-water, and Antarctica in the geotiff and ascii files have the no-data value of −9999. Exception, MERIT_plus_05min_v1_flwdir.tif, has nodata value of 247.
File format: tab delimited (.csv)
File naming convention: MERIT_plus_05min_flwdir_v1_{Variable}.csv
Where {Variable} is one of: IDs or IDsEnR
Units:
IDs: None
IDsEnR: None
Repository: MSD-LIVE, Project: Program on Coupled Human and Earth Systems (PCHES) https://msdlive.org/projects/pches
Missing data codes:
Nodata values are -9999 except for
byte type
flow direction datasets in GeoTIFF format which have values of 243.
Other
Date of data collection: Data created 0n December 17, 2021
Geographic location of data collection: This data is global.
Information about funding sources that supported the collection of the data:
This material was based upon work supported by the U.S. Department of Energy, Office of Science, Biological and Environmental Research Program, Earth and Environmental Systems Modeling, MultiSector Dynamics under Cooperative Agreement DE-SC0022141 and DE-SC0022141.; the National Aeronautical and Space Administration, Earth Science Division's High Mountain Asia program (grant no. 80NSSC20K1595), and the Earth Science Division's Sea Level Change program (grant no. 80NSSC20K1296); and the Swedish funding agency Formas (grant no. 2017-00,608).
Recommended citation for this dataset:
Prusevich, A.A., Lammers, R.B. , (2022) MERIT-Plus Dataset, version 1 (DOI:10.57931/1904379)
Relationship between files:
Each set of files, named with the spatial resolution of the data, (5 or 15 arc minutes), has one master file, the flow direction, and all other files are derivatives of this flow direction grid such as basin IDs and upstream area. Attribute files are also included for each of the grid cell resolutions which include attributes for all basins and for endorheic basins only.
Basin ID values are derived from sorted (largest to smallest) basin area (e.g. the largest basin is the Amazon with an ID=1, followed by the Congo with an ID=2, etc. The endorheic basin ID subset retains ID values from the complete basin ID data.
People involved with sample collection, processing, analysis and/or submission:
Stanley Glidden assisted with data submission into this database and writing this document.
Specialized formats or other abbreviations used:
WBM - Water Balance Model
EnR - Suffix in the filenames which stands for "endorheic".
Future plans for this database:
Depending on the needs of specific research projects, we may be required to alter the flow direction of some river lines and additional MERIT-Plus data in Global or regional geographical extents and resolutions may be added to the repository. We will consider requests by users of this data.
References
Eilander, D., van Verseveld, W., Yamazaki, D., Weerts, A., Winsemius, H. C., & Ward, P. J. (2021). A hydrography upscaling method for scale-invariant parametrization of distributed hydrological models. Hydrol. Earth Syst. Sci., 25(9), 5287-5313. doi:10.5194/hess-25-5287,2021
Grogan, D. S., Zuidema, S., Prusevich, A., Wollheim, W. M., Glidden, S., & Lammers, R. B. (2022). Water balance model (WBM) v.1.0.0: a scalable gridded global hydrologic model with water-tracking functionality. Geosci. Model Dev., 15(19), 7287-7323. doi:10.5194/gmd-15-7287-2022
KÃ¥resdotter, E., Destouni, G., Ghajarnia, N., Lammers, R. B., & Kalantari, Z. (2022). Distinguishing Direct Human-Driven Effects on the Global Terrestrial Water Cycle. Earth's Future, 10(8). doi:ARTN e2022EF002848 / 10.1029/2022EF002848
OpenStreetMap, C. (2022). OpenStreetMap database [PostgreSQL via API]. Retrieved December 2022, from OpenStreetMap Foundation, Cambridge, UK
Wikipedia, C. (2022). Endorheic basin. The Free Encyclopedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Endorheic_basin&oldid=1125640616
Yamazaki, D., Ikeshima, D., Sosa, J., Bates, P. D., Allen, G. H., & Pavelsky, T. M. (2019). MERIT Hydro: A High-Resolution Global Hydrography Map Based on Latest Topography Dataset. Water Resources Research, 55(6), 5053-5073. doi:https://doi.org/10.1029/2019WR024873
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