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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Sciences Discussions Earth System and . in area, contain 98.64% of the ◦ 2 1930 1929 from the Hydrosheds Shuttle Radar Topography digital elevation model 2 The Hydrosheds project (Lehner et al., 2008a, b) created a hole-filled version of Geomorphometry performs quantitative land-surface analysis (Pike et al., 2009), This discussion paper is/has beenSystem under Sciences review for (HESS). the Please journal refer to Hydrology the and corresponding Earth final paper in HESS if available. and the SRTM dataGuth provides (2006) a looked data at set 12 at key an geomorphometric appropriate parameters scale from for SRTM global to analyses. compare the SRTM DEM, conditioneddrainage network the and dataset basins outlines for fromset hydrologic a includes 15 applications, 3.46 arc million and second stream version segments releasedsmall of in and SRTM. a 2.48 This million contain data basins; at most mosta of one the node stream basins being are segment. eitherlargest A the 1.06% segment terminus of connects the of two basins, asegments. nodes, those segment with over 100 or km the junction of two segments. The voids in mountainous terrainbest and freely sandy available desert dataset regions,et and the al., several projects SRTM 2008; have DEM Lehnercoverage worked remains for et to Antarctica the al., fill and the latitudes 2008a, north voids b). of (Jarvis 60 The SRTM’s greatest weakness is the lack of basin, and the scaledrainage of basins the display digital the elevationtend typical model to be used longitudinal more for stream convex the than profiles, computations. the but smaller the These basins. major basins 1 Introduction The Shuttle Radar Topography Missionmodel (SRTM) (DEM) created with a 3 near arc global second digital spacing, elevation about 90 m (Farr et al., 2007). Despite some A suite of 42than geomorphometric 100 parameters km for eachshows of the 26 272 global drainage distributionlargest basins basins of larger are Strahler order order 9. for Many common parameters and depend drainage both basins; on the the size of the Abstract Hydrol. Earth Syst. Sci.www.hydrol-earth-syst-sci-discuss.net/8/1929/2011/ Discuss., 8, 1929–1949, 2011 doi:10.5194/hessd-8-1929-2011 © Author(s) 2011. CC Attribution 3.0 License. Geomorphometry of drainage basins: a global view from theTopography Shuttle Mission Radar P. L. Guth Department of Oceanography, US Naval Academy, Annapolis, MD, USA Received: 3 January 2011 – Accepted:Correspondence 30 to: January 2011 P. L. – Guth Published: ([email protected]) 16 FebruaryPublished 2011 by Copernicus Publications on behalf of the European Geosciences Union. 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ff erent ff respec- removes 464 m at 2 2 × and 0.1 km 2 DEM used to compute the 00 461 m at the equator and 232 erent scales. erences in total basin relief (6211, 3955, × ff ff , clearly demonstrating a logarithmic decline . With the 15 2 1932 1931 2 and most of these have no segments. 2 ): a great many tiny basins along the coast with no stream seg- 2 contains 500–1000 elevation points. These basins 2 100 km < , the limit of the SRTM data. These represent about 0.2 km ◦ Figure 5 shows maps color-coded by 4 of the basin geomorphometric parameters Figure 2 compares the Hydrosheds drainage network with the medium resolution The scale of the DEM used to create the drainage network limits the scale of features Computed (the major channel in the basin) are based solely on landforms This study seeks to use the Hydrosheds drainage basins, natural sampling areas listed in Appendix B. Like Fig. 3, the map visually emphasizes the large basins. On Figure 3 shows the drainage basinson coded earth by Strahler (Amazon, order. The Congo,geomorphic three and largest regimes streams Volga) due haveand a to 1624 Strahler m significant respectively). order di Figure ofbasins 4 9, with shows an and a area histogram very greaterin of di than the Strahler 100 number order km of for basins themany with 26 small 272 increasing order order. 1 streams; Limitinglarger an basin streams. alternative size might to be 100 km to restrict analysis to order 2 and ments, and a much smallerbetween number the of outlets first of and the some larger second basins. order drainage networks 3 Results network from the US National HydrographyAt Dataset regional (NHD; scales Simley they and line Carswell, up 2009). generally very shows well, additional and because . thelandforms The NHD reflects number and a of the larger additional scale, resulting tributaries it that channel the varies Strahler patterns. with order 1 Brief streamsand in qualitative most this assessment commonly region suggests are range fromsmall order order basins 2 1 ( or to 4 3. in Figure the NHD 2 data, also shows the bimodal distribution of algorithm can be fooledproportional in to cases area; where thelowing climate Nile, the does highlighted Bahr not in el produceNile, Fig. Ghazal instead rainfall 1, and of and shows Bahr following runo the the al-Arabset water computed west precludes up a into the manual fol- Darfur, Blue search tributaries Nile. to of correct The the this number limitation. White of basins in the data upstream, at each junction taking the with the larger contributing area. This most always dry. Thehas the thalwegs largest start contributing from area and the no last downstream connections. segment I in trace the the thalweg basin, which Most of these small(Fig. basins 1). occur on the coastline, or large areasvisible of in interior the drainage drainagea networks. half kilometer, The and smallest willcomparing segments influence these will results parameters be with like a those , so from single di care pixel, must about bein taken the in SRTM data, and not on hydrology; some channels might be intermittent or al- 60 tively, so a 100 km are likely to have onlythis a size single limit channel, is and somewhat producedrosheds arbitrary, statistics have over of areas 85% limited less of validity. the While than drainage 1 km basins identified by Hy- rics of the drainagethalwegs. basin and channel networks, and characteristics of the2 channel Methods and limitations Appendix A listsbasins the with processing steps andrainage used area network, with less each the than pixel Hydrosheds is 100 km data. about 464 I excluded computed worldwide from SRTM (Guth,lar 2009). areas (0.5 Those million analyses inconsidered used the random small United sampling rectangu- States, areas. 7.4 million in the entireof world) varying which size, can and be computes both geomorphometric parameters from the DEM, met- results with the US National Elevation Dataset, and further described 30 parameters 5 5 25 20 10 15 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 00 data 00 RUGD, which is the data, appropriate for RELF (Fig. 5a) is the 00 scale by using the full resolution of the 00 1934 1933 RELF parameter, which considers only the geometry 0.90 mostly demonstrate that many of the parameters > erent ways of expressing slope; the one correlation that is not directly ff ASTER GDEM do not appear to be substantiated (Guth, 2010), and even the 1 Figure 8 shows a correlation matrix for the 42 parameters in Appendix B, for all 26 272 Figures 6 and 7 look at basin thalwegs, on a normalized plot of elevation and distance 00 for geomorphometry (Guth, 2006). applications. He emphasizedDEM that quality, and the its results scale.global of The analysis, using results but reported DEMs could here dependedSRTM rely be data. on on extended 15 both to The the coverage 3 most at significant high problem northernfor will latitudes, a be but global the the dataset holes1 SRTM for appears in the to the be immediate data,SRTM the future. data and best currently lack restricted candidate Initial of tofor claims the the for United continental States the United military States superiority and does of publicly not available provide the only much improvement over the 3 sures. 4 Discussion Wechsler (2007) looked at uncertainties in DEMs and how they impacted hydrologic thalwegs, such as the Indus, show several distinct convex segments. basins. Blue represents thelations. strength Positive of correlations positivereally correlations, reflect and di red negativerelated corre- to slope is aorder. high correlation The between the strongest log negativecorrelated of correlations with the are basin the area for slope and S2S3 the measures and Strahler because STRENGTH, they negatively are defined as inverse slope mea- are working on a satisfactorythalwegs. automatic filtering A algorithm that numberin will of work Fig. with the 6; all thalwegsheadwaters, 26 for 272 while in example, the Fig. Nelson both 7 haswell the as an lie much Amazon extremely lower outside abrupt and overall descent the relief Niger into compared common Hudson’s to (Fig. Bay, zones the as 7b) others seen in have this extremely group. Several steep of these noise in the measured elevations where the channel goes through deep ; we over 500 m relief along the thalweg, and Strahler order 8 or 9). The graphs exhibit so that profileshapes, shapes in can terms be ofless compared. the than percentage 1 Figure of are basin 65. not in contours shown, each Profiles the and percent the density tendheadwaters, on reflecting magenta of the to the includes graph. traditional thalweg be values gradedFig. very Densities profile. significantly 6a, The larger gentle tend small to than near have basins, a whichdownstream the much dominate more segment, mouth linear profile; steeper of the largerseen headwaters, the streams in tend Fig. and river, to 6b. have an and Figure a 7 flatter overall steep shows the more near thalwegs of concave the the profile 25 largest as basins (defined as having the huge range in values36 for for this small parameter, from steepstraight nearly basins. thalweg 0 and for Figure higher very 5d valuesthat large, shows for flat appears curved basin basins at channels. SINUOSITY, to with this Thedistance low most of scale 521 sinuous values is km. major for the river a Don, which curves 1896 km to travel a straight line Sea, and a thalweg whichSea. descends Figure comparatively 5b rapidly shows the nearof RATIO its the mouth thalweg at and thein in Black essence small computes steep itslargest basins average values which slope. are do The fromhigh not largest the into values show occur Mekong the up and centralratio well Yangtze, Asian of at which basin’s mountains. elevation have this range thalwegsalong Figure scale; to coasts that its 5c of and area, ascend shows interior and major BASIN basins this , in metric central rewards the Asia; small, steep coloring basins by the logarithm emphasizes Great Basin, Sahara, Arabianlack peninsula, large drainage central basins, Asia, in both andelevation-relief area ratio western and computed Australia) Strahler from order. tend the ELEV value to DEM. of The this Dnieper parameter, River due basinmiddle to has an of the elevation the largest distribution elevation with distribution almost all and the very points little in area the near the elevation of the Black all of these maps, several characteristics stand out. The desert belts (North American 5 5 25 20 10 15 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 00 Hydrosheds database. 00 from the 15 2 SRTM data created by decimating the 00 1936 1935 (about 0.5 km), appropriate for global studies. Because 00 DEM produces similar results). 00 , and provides a near-global, internally consistent data set to investigate 2 Hydrosheds void-filled data. This size allows in memory manipulation of the 00 Assign each drainage segment to ain basin the using small a point drainage in basins area are function; left segments unassigned. Create thalweg for each basinHydrosheds as DEM a 3-D (6 shapefile with the elevations fromCompute the 15 geomorphometric parameters listedbasin. in Appendix B for eachModify Hydrosheds drainage river files toorder, include and the whether basin it to lies which on the it thalweg belongs,Modify of its the the Strahler drainage Hydrosheds system. basinchannels in files the to basin, the include length Strahler of the order, thalweg, the and the total perimeter length of the of basin. Create a DEM for3 each basin, usinglargest 6 drainage basins for fastdrainage processing, basins. and is still higher resolution than the Extract nodes and createeach topology drainage segment, for and each compute basin its from Strahler order the nodes at the end of Manually identify significant basinsmaterial. by reference to atlases and other reference Remove basins with areas less thanThis 100 reduced km the 2.48 million basins in the original data set to 26 272. Create a basin identifierHydrosheds for with each a basin, two whichsets digit combines for code the each for basin basin the and number continent, looking from which at allows multiple linking continents simultaneously. the data Despite the limitations of scale and data quality, the SRTM drainage data provides a 6. 7. 9. 3. 4. 5. 8. 2. 1. 10. Appendix A cannot be readilyof compared the to drainage other basinprovides studies. as a fascinating well Parameters picture as of also the the depend resolution world’s drainage on of patterns. the the input size data, but the SRTM data 5 Conclusions The SRTM-derived Hydrosheds datathan set 100 contains km 26 272 basinsthe with gemorphological properties an of area both greater resolution the of basin this and the datamost thalweg is parameters profiles. 15 depend The on the scale of the data used for computations, these results real bonanza for quantitative . Thecomparisons, challenge which will be will to probably frame involve theor restricting correct Strahler analysis order, to and basins looking at withdata the similar from subbasins size SRTM within consists the globalallows of data manipulation about set. on 35 The common GB elevation desktop of computers. data, and cheap processing and storage Processing steps 5 5 10 15 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | DEM). 00 DEM). 00 DEM). 00 DEM). Slope computed with DEM). 00 DEM). 00 DEM). DEM). DEM). DEM). 00 DEM). Computed with equations in 00 00 00 DEM). DEM). 00 00 00 cient of dissection erence from each point to its nearest 00 DEM). Computed with the equations in ff ffi 00 DEM). DEM). 00 DEM). DEM). 00 1938 1937 DEM). 00 00 DEM). 00 00 Min Elevation]/RELIEF) − NESW: Nugget variance, northeast-southwest direction. EW: Nugget variance from the variogram (Curran, 1988), east-west di- NS: Nugget variance, north-south direction. AVG: average profile curvature (6 STD: standard deviation of profile curvature (6 SKW: skewness of profile curvature (6 KRT: kurtosis of profile curvature (6 MAX: maximum slope in percent (6 AVG: Steepness or Roughness, average slope (6 STD: standard deviation of slope (6 SKW: skewness of slope (6 KRT: kurtosis of slope (6 AVG: average plan curvature (6 STD: standard deviation of plan curvature (6 SKW: skewness of plan curvature (6 KRT: kurtosis of plan curvature (6 AVG RELF: Elevation- or coe AVG: average elevation (6 STD: standard deviation of elevation (6 SKW: skewness of elevation (6 KRT: kurtosis of elevation (6 MAX: maximum elevation (6 DEM) 00 GAMMA GAMMA rection. This measuresneighbor; the smaller elevation values reflect di (6 smooth , and high values rougher terrain SHAPE: alternate formulation for terrain(Fisher organization et al., 1987, p. 48, 159). PROFC PROFC PLANC Wood (1996) based on earlier suggestions fromPLANC Evans. PLANC PLANC GAMMA S2S3: terrain organization (Guth,dency for 2003). ridges and High valleys values to correlate align. STRENGTH: with alternate strong formulation ten- for flatness (Fisher et al., 1987, p. 48, 159). ROUGHNESS: strong correlation with slope (Mark, 1975;PROFC Etzelmuller, 2000). Wood (1996) based on earlier suggestions from Evans. PROFC NPTS: number of points in drainage basin (6 ELEV ELEV RELIEF: elevation range [MaxZ – MinZ] (6 ELEV ELEV ([ELEV (Pike and Wilson, 1971; Etzelmuller, 2000; Strahler, 1952). SLOPE Evans (1998) method, modified for DEM spacing in arc seconds. SLOPE SLOPE S1S2: flatness, or slope inverse (Guth, 2003). ELEV ELEV SLOPE SLOPE 1. 2. 7. 9. 3. 4. 5. 6. 8. 28. 29. 24. 25. 26. 27. 16. 17. 18. 19. 20. 22. 23. 15. 21. 11. 12. 13. 10. 14. Appendix B Geomorphometric parameters 5 5 20 15 10 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , DEM). DEM). drainage 00 00 00 ). http://srtm.csi.cgiar.org geomorph.htm , 2003. KM RUGD 1940 1939 SQKM er, S., Shimada, J., Umland, J., Werner, M., Oskin, drainage basin. ff 00 , 2007. TH (m)/THALWEG http://gisdata.usgs.gov/webappcontent/HydroSHEDS/downloads/ erence in elevation (m) along the basin thalweg. ff I thank the World Wildlife Foundation and United States Geological Sur- O: Strahler order (Strahler, 1957) computed from the 15 KM: length of the basin’s thalweg. KM: total length of channels in drainage basin. KM: perimeter of 15 NWSE: Nugget variance, northwest-southeast direction. 30: percentage of drainage basin with slope50: exceeding 30% percentage (6 of drainage basin with slope exceeding 50% (6 TH: di RUGD: RELIEF (m)/AREA REL: RELIEF SQKM: basin area. RUGD: log base 10 of BASIN OV OV http://www.terrapub.co.jp/e-library/ohmori/pdf/199.pdf PERIMTR RATIO STRAHLER network. Sometimes called the Strahler-Horten order. SINUOSITY: ratio of thalwegendpoints. length to straight line distance connecting thalweg SLP SLP AREA RELIEF BASIN LOG GAMMA THALWEG CHANNEL available from the CGIAR-CSI SRTM 90m Database, available at: cations, edited by: Hengl, T. andAmsterdam, Reuter, 351–366, H. 2009. I., Developments in Soil Science Series, Elsevier, Fall Specialty Conference, Orlando, FL, November 15–19, Conference CD-ROM, 2010. 2008. tion data, EOS, 89, 93–94, 2008a. sion 1.1, available at: 72, 269–277, 2006. University Press, 330 p, 1987. Modelling in Geomorphology: InternationalTokunaga, Perspectives, E., edited Ohmori, by: H., Evans,at: and I. Hirano, S., M., Dikau, Terrapub R., Publishers, Tokyo, 199–220, available doi:10.1029/2005RG000183 analysis, edited by: in Lane,119–138, S. 1998. N., Richards, K. S., and Chandler, J. H.,Rodriguez, J. Wiley, E., Chichester, Roth, L.,M., Seal, Burbank, D., D., and Sha Alsdorf, D.: The shuttle radar topography mission, Rev. Geophys., 45, els (DEMs), Transactions in GIS, 4, 129–143, 2000. 24, 493–507, 1988. 40. 41. 42. 38. 32. 33. 37. 39. 31. 34. 36. 30. 35. http://www.usna.edu/Users/oceano/pguth/srtm/hydrosheds Jarvis, A., Reuter, H. I., Nelson, A., and Guevara, E.: Hole-filled SRTM for the globe Version 4, Guth, P. L.: Geomorphometric comparison of ASTER GDEM and SRTM, ASPRS/CaGIS, 2010 Lehner, B., Verdin, K., and Jarvis, J.: HydroSHEDS Technical Documentation Ver- Lehner, B., Verdin, K., and Jarvis, J.: New global hydrography derived from spaceborne eleva- Guth, P. L.: Geomorphometry in MICRODEM, in: Geomorphometry: concepts, software, appli- Guth, P. L.: Geomorphometry from SRTM: Comparison to NED, Photogramm. Eng. Rem. S., Guth, P. L.: Terrain organization calculated from digital elevation models, in: Concepts and Fisher, N. L, Lewis, T., and Embleton, B. J. J.: Statistical analysis of spherical data, Cambridge Farr, T. G., Rosen, P. A., Caro, E., Crippen, R., Duren, R., Hensley, S., Kobrick, M., Paller, M., Evans, I. S.: What do terrain statistics really mean?, in: Landform monitoring, modelling and Etzelmuller, B.: On the quantification of surface changes using grid-base digital elevation mod- Curran, P. J.: The semivariogram in remote sensing: an introduction, Remote Sens. Environ., References Acknowledgements. vey for creatinghave and been done distributinglines without the and their Hydrosheds geomorphometric work. data( parameters, set; Shapefiles and for 3-D obviously the basin this river thalwegs work networks, can drainage could be basin not downloaded out- from 5 5 25 30 20 15 10 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , , jwo/phd/ ∼ , 2009. for Africa, with the thalwegs 2 doi:10.5194/hess-11-1481-2007 http://www.soi.city.ac.uk/ 1942 1941 http://pubs.usgs.gov/fs/2009/3054/ , 2008b. v11.pdf TechDoc Red symbols mark drainage basins smaller than 100 km Strahler order for the larger channels in Africa, down to order 4. Bull., 63, 1117–1142, 1952. can Geophysical Union, 8, 913–920, 1957. tions: a review, Hydrol. Earth Syst. Sci., 11, 1481–1500, PhD Thesis, University1996. of Leicester, UK, available at: Science Series, Elsevier, 1–30, 2009. Fact Sheet 2009–3054, p. 4, available at: 2007. HydroSHEDS altitude analysis, Geol. Soc. Am. Bull., 82, 1079–1084, 1971. concepts, software, applications, edited by: Hengl, T. and Reuter, H. I., Developments in Soil 57A, 165–177, 1975. ectively mark the coastline, with smaller numbers in interior drainage areas such as the ff Fig. 1. (a) of the larger drainage basinse shown in blue. TheSahara. Nile is The highlighted in(b) size black. of The small the basins symbols greatly exaggerates the importance of the small basins. Strahler, A. N.: Quantitative analysis of watershed geomorphology, TransactionsWechsler, of S. the P.: Ameri- Uncertainties associated with digital elevation models for hydrologic applica- Wood, J. D.: The geomorphological characterisation of digital elevation models: unpublished Simley, J. D. and Carswell Jr., W. J.: TheStrahler, National A. Map N.: – Hydrography, Hypsometric US Geological (area-altitude) Survey analysis of erosional topography, Geol. Soc. Am. Pike, R. J., Evans, I. S., and Hengl, T.: Geomorphometry: A brief guide, in: Geomorphometry: Pike, R. J. and Wilson, S. E.: Elevation-relief ratio, hypsometric integral and geomorphic area- Mark, D. M.: Geomorphometric parameters: A review and evaluation, Geografiska Annaler, 5 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1944 1943 Comparison of Hydrosheds and NHD drainage networks for part of the Chesapeake Strahler order for the largest segment in global drainage basins. Fig. 3. Fig. 2. Bay watershed. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | RELF, Basin area (log scale) (c) RATIO (b) RELF, ELEV (a) 1946 1945 Histogram of basin area. (b) SINUOSITY. (d) Histogram of Strahler order. RUGD, and Maps with drainage basin parameters. LOG Fig. 5. (c) Fig. 4. (a) versus Strahler order. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | DEM instead of the 500 m, Strahler order 00 > and those of Strahler order 4 (a) labeled thalwegs for 5 channels; (b) 1948 1947 DEM used to compute the drainage basins. 00 . Colors range from 1% (blue) to 5% or greater (violet). Note the displacement (b) normalized basin profiles for all 25 thalwegs; Normalized longitudinal thalweg profiles for all basins (a) Thalwegs for the 25 largest global drainage basins (thalweg relief 8): locations for the thalwegs. Elevation spikes result from using the 6 = Fig. 7. > (c) hydrologically conditioned 15 downward and to the right for the larger basins. and larger Fig. 6. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1949 . Correlation matrix for the parameters in Appendix B for all drainage basins larger than 2 Fig. 8. 100 km