The world’s rivers deliver 19 billion tonnes of sediment to the coastal zone annually1, with a considerable fraction being sequestered in large deltas, home to over 500 million people. Most (more than 70 per cent) large deltas are under threat from a combination of rising sea levels, ground surface subsidence and anthropogenic sediment trapping2,3, and a sustainable supply of fluvial sediment is therefore critical to prevent deltas being ‘drowned’ by rising relative sea levels2,3,4. Here we combine suspended sediment load data from the Mekong River with hydrological model simulations to isolate the role of tropical cyclones in transmitting suspended sediment to one of the world’s great deltas. We demonstrate that spatial variations in the Mekong’s suspended sediment load are correlated (r = 0.765, P < 0.1) with observed variations in tropical-cyclone climatology, and that a substantial portion (32 per cent) of the suspended sediment load reaching the delta is delivered by runoff generated by rainfall associated with tropical cyclones. Furthermore, we estimate that the suspended load to the delta has declined by 52.6 ± 10.2 megatonnes over recent years (1981–2005), of which 33.0 ± 7.1 megatonnes is due to a shift in tropical-cyclone climatology. Consequently, tropical cyclones have a key role in controlling the magnitude of, and variability in, transmission of suspended sediment to the coast. It is likely that anthropogenic sediment trapping in upstream reservoirs is a dominant factor in explaining past5,6,7, and anticipating future8,9, declines in suspended sediment loads reaching the world’s major deltas. However, our study shows that changes in tropical-cyclone climatology affect trends in fluvial suspended sediment loads and thus are also key to fully assessing the risk posed to vulnerable coastal systems.
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Milliman, J. D. & Farnsworth, K. L. River Discharge to the Coastal Ocean: A Global Synthesis (Cambridge Univ. Press, 2011)
Ericson, J. P., Vörösmarty, C. J., Dingman, S. L., Ward, L. G. & Meybeck, M. Effective sea-level rise and deltas: causes of change and human dimension implications. Global Planet. Change 50, 63–82 (2006)
Syvitski, J. P. M. et al. Sinking deltas due to human activities. Nat. Geosci. 2, 681–686 (2009)
Darby, S. E., Dunn, F. E., Nicholls, R. J., Rahman, M. & Riddy, L. A first look at the influence of anthropogenic climate change on the future delivery of fluvial sediment to the Ganges–Brahmaputra–Meghna delta. Environ. Sci. Process. Impacts 17, 1587–1600 (2015)
Vörösmarty, C. J. et al. Anthropogenic sediment retention: major global impact from registered river impoundments. Global Planet. Change 39, 169–190 (2003)
Walling, D. E. & Fang, D. Recent trends in the suspended sediment loads of the world’s rivers. Global Planet. Change 39, 111–126 (2003)
Wang, S. et al. Reduced sediment transport in the Yellow River due to anthropogenic changes. Nat. Geosci. 9, 38–41 (2016)
Kummu, M. J., Wang, J. J., Lu, X. X. & Varis, O. Basin-wide sediment trapping efficiency of emerging reservoirs along the Mekong. Geomorphology 119, 181–197 (2010)
Kondolf, G. M., Rubin, Z. K. & Minear, J. T. Dams on the Mekong: cumulative sediment starvation. Wat. Resour. Res. 50, 5158–5169 (2014)
Richey, J. E., Brock, J. T., Naiman, R. J., Wissmar, R. C. & Stallard, R. F. Organic carbon: oxidation and transport in the Amazon River. Science 207, 1348–1351 (1980)
Aufdenkampe, A. K. et al. Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere. Front. Ecol. Environ 9, 53–60 (2011)
Day, J. W. Jr et al. Restoration of the Mississippi Delta: lessons from hurricanes Katrina and Rita. Science 315, 1679–1684 (2007)
Duc, D. M., Nhuan, M. T. & Ngoi, C. V. An analysis of coastal erosion in the tropical rapid accretion delta of the Red River, Vietnam. J. Asian Earth Sci. 43, 98–109 (2012)
Milliman, J. D. & Kao, S. J. Hyperpycnal discharge of fluvial sediment to the ocean: impact of super-typhoon Herb (1996) on Taiwanese rivers. J. Geol. 113, 503–516 (2005)
Dadson, S. J. et al. Links between erosion, runoff variability and seismicity in the Taiwan orogen. Nature 426, 648–651 (2003)
Hilton, R. G. et al. Tropical-cyclone driven erosion of the terrestrial biosphere from mountains. Nat. Geosci. 1, 759–762 (2008)
Terry, J. P., Garimella, S. & Kostaschuk, R. A. Rates of floodplain accretion in a tropical island river system impacted by cyclones and large floods. Geomorphology 42, 171–182 (2002)
Amos, K. J. et al. Supply limited sediment transport in a high-discharge event of the tropical Burdekin River, North Queensland, Australia. Sedimentology 51, 145–162 (2004)
Aalto, R. et al. Episodic sediment accumulation on Amazonian flood plains influenced by El Niño/Southern Oscillation. Nature 425, 493–497 (2003)
Mekong River Commission. Overview of the Hydrology of the Mekong River Basin (Mekong River Commission, 2005)
Milliman, J. D. & Meade, R. H. World-wide delivery of river sediment to the oceans. J. Geol. 91, 1–21 (1983)
Anthony, E. J. et al. Linking rapid erosion of the Mekong River delta to human activities. Sci. Rep. 5, 14745 (2015)
Kummu, M. & Varis, O. Sediment-related impacts due to upstream reservoir trapping on the Lower Mekong River. Geomorphology 85, 275–293 (2007)
Lu, X. X., Kummu, M. & Oeurng, C. Reappraisal of sediment dynamics in the Lower Mekong River, Cambodia. Earth Surf. Process. Landf. 39, 1855–1865 (2014)
Wang, J. J., Lu, X. X. & Kummu, M. Sediment load estimates and variations in the lower Mekong River. River Res. Appl. 27, 33–46 (2011)
Darby, S. E., Leyland, J., Kummu, M., Räsänen, T. A. & Lauri, H. Decoding the drivers of bank erosion on the Mekong river: the roles of the Asian monsoon, tropical storms, and snowmelt. Wat. Resour. Res. 49, 2146–2163 (2013)
Manh, N. V., Dung, N. V., Hung, N. N., Merz, B. & Apel, H. Large-scale suspended sediment transport and sediment deposition in the Mekong delta. Hydrol. Earth Syst. Sci. 18, 3033–3053 (2014)
Kontgis, C., Schneider, A. & Ozdogan, M. Mapping rice paddy extent and intensification in the Vietnamese Mekong River Delta with dense time stacks of Landsat data. Remote Sens. Environ. 169, 255–269 (2015)
Brunier, G., Anthony, E. J., Goichot, M., Provansal, M. & Dussouillez, P. Recent morphological changes in the Mekong and Bassac river channels, Mekong Delta: the marked impact of river-bed mining and implications for delta destabilisation. Geomorphology 224, 177–191 (2014)
Redmond, G., Hodges, K. I., Mcsweeney, C., Jones, R. & Hein, D. Projected changes in tropical cyclones over Vietnam and the South China Sea using a 25 km regional climate model perturbed physics ensemble. Clim. Dyn. 45, 1983–2000 (2015)
Nittrouer, J. A. & Viparelli, E. Sand as a stable and sustainable resource for nourishing the Mississippi River delta. Nat. Geosci. 7, 350–354 (2014)
Koponen, J. H. et al. HBV and IWRM Watershed Modelling User Guide (MRC Information and Knowledge Management Programme, 2010)
Lauri, H. et al. Future changes in Mekong River hydrology: impact of climate change and reservoir operation on discharge. Hydrol. Earth Syst. Sci. 16, 4603–4619 (2012)
Lauri, H. VMod 5km Grid Hydrological Modeling Report (EIA Ltd.) (Aalto Univ., 2009)
Jarvis, A. H. et al. Hole-Filled Seamless SRTM Data Version 4 (The CGIAR Consortium for Spatial Information, 2008)
IES. Global Land Cover 2000 (IES, 2000)
Food and Agricultural Organization of the United Nations. WRB Map of World Soil Resources (FAO, 2003)
Mekong River Commission. Hydrometeorological Database of the Mekong River Commission (Mekong River Commission, 2011)
US National Climatic Data Center. Global Surface Summary of the Day (GSOD) (NCDC, 2010)
Nash, J. E. & Sutcliffe, J. V. River flow forecasting through conceptual models part I—a discussion of principles. J. Hydrol. (Amst.) 10, 282–290 (1970)
Henriksen, H. J. et al. Assessment of exploitable groundwater resources of Denmark by use of ensemble resource indicators and a numerical groundwater–surface water model. J. Hydrol. (Amst.) 348, 224–240 (2008)
Knapp, K. R. et al. The international best track archive for climate stewardship (IBTrACS): Unifying tropical cyclone best track data. Bull. Am. Meteorol. Soc. 91, 363–376 (2010)
Rodgers, E. B. et al. Contribution of tropical cyclones to the North Pacific climatological rainfall as observed from satellites. J. Appl. Meteorol. 39, 1658–1678 (2000)
Englehart, P. J. & Douglas, A. V. The role of eastern North Pacific tropical storms in the rainfall climatology of western Mexico. Int. J. Climatol. 21, 1357–1370 (2001)
Kubota, H. & Wang, B. How much do tropical cyclones affect seasonal and inter-annual rainfall variability over the Western North Pacific? J. Clim. 22, 5495–5510 (2009)
Bell, G. D. et al. Climate assessment for 1999. Bull. Am. Meteorol. Soc. 81, s1–s50 (2000)
Emanuel, K. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436, 686–688 (2005)
Webster, P. J., Holland, G. J., Curry, J. A. & Chang, H. R. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science 309, 1844–1846 (2005)
Ferguson, R. I. River loads underestimated by rating curves. Wat. Resour. Res. 22, 74–76 (1986)
Walling, D. E. Evaluation and Analysis of Sediment Data from the Lower Mekong River (Mekong River Commission, 2005)
Walling, D. E. The changing sediment load of the Mekong River. Ambio 37, 150–157 (2008)
Turowski, J. M., Rickenmann, D. & Dadson, S. J. The partitioning of the total sediment load of a river into suspended load and bedload: a review of empirical data. Sedimentology 57, 1126–1146 (2010)
Kostaschuk, R. J. et al. Measurement of flow velocity and sediment transport with an acoustic Doppler current profiler. Geomorphology 68, 25–37 (2005)
Szupiany, R. N. et al. Morphology, flow structure and suspended bed sediment transport at two large braid-bar confluences. Wat. Resour. Res. 45, W05415 (2009)
Shugar, D. et al. On the relationship between flow and suspended sediment transport over the crest of a sand dune, Rio Parana, Argentina. Sedimentology 57, 252–272 (2010)
Van Dorn, W. G. Large-volume water samplers. Eos Trans. AGU 37, 682–684 (1956)
Bravard, J.-P., Goichot, M. & Tronchère, H. An assessment of sediment-transport processes in the Lower Mekong River based on deposit grain sizes, the CM technique and flow-energy data. Geomorphology 207, 174–189 (2014)
Räsänen, T. & Kummu, M. Spatiotemporal influences of ENSO on precipitation and flood pulse in the Mekong River Basin. J. Hydrol. (Amst.) 476, 154–168 (2013)
Ward, P. J. et al. Annual flood sensitivity to El Niño Southern Oscillation at the global scale. Hydrol. Earth Syst. Sci. 18, 47–66 (2014)
Kendall, M. G. A new measure of rank correlation. Biometrika 30, 81–93 (1938)
This study was supported by awards NE/JO21970/1, NE/JO21571/1 and NE/JO21881/1 from the UK Natural Environmental Research Council (NERC) and the Academy of Finland funded project SCART (grant number 267463). We thank the Mekong River Commission for access to hydrological and suspended sediment data and the Department for Hydrology and Water Resources in Cambodia for aDcp data and their logistical support. J.L.B. was also in receipt of a University of Southampton Diamond Jubilee Fellowship and National Great Rivers Research and Education Centre Fellowship that aided completion of this work.
The authors declare no competing financial interests.
Reviewer Information Nature thanks L. Giosan and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
The numbers identify the basins listed in Extended Data Table 1. Note that the Ganges (basin 19) and Brahmaputra (basin 28) catchments are outlined as a single basin in the figure. Also shown is the density of all TC tracks from 1842 to 2015 as recorded in the IBTrACS42 database. Track density was calculated using the point density function in ArcGIS 10.1.
Extended Data Figure 2 Sediment rating curves for the five river gauging stations on the Lower Mekong River.
a, c, e, g, i, The relationship between flow discharge (Q) and suspended solids concentration (C) at: Luang Prabang (pre-dam: n = 187, r2 = 0.338; post-dam: n = 49, r2 = 0.648) (a); Mukdahan (n = 1,159, r2 = 0.497) (c); Pakse (n = 60, r2 = 0.591) (e); Stung Treng (n = 95, r2 = 0.870) (g); and Kratie (n = 140, r2 = 0.850) (i). b, d, f, h, j, These panels show how the relationships in a, c, e, h and i propagate through to give the relationship between flow discharge (Q) and instantaneous sediment load (Qs) at the same stations: Luang Prabang (pre-dam: n = 187, r2 = 0.791; post-dam: n = 49, r2 = 0.864) (b); Mukdahan (n = 1,159, r2 = 0.693) (d); Pakse (n = 60, r2 = 0.780) (f); Stung Treng (n = 95, r2 = 0.900) (h); and Kratie (n = 140, r2 = 0.931) (j). All the fits shown are significant at P < 0.00001. Note that the scales for a and b (Luang Prabang) differ from those for the other panels. We recognize that the fits for Q versus Qs in b, d, f, h and j are stronger than the fits between Q and C because of the auto-correlation arising when transforming C to Qs (Qs = C × Q/1,000). For the stations at Mukdahan, Pakse, Stung Treng and Kratie, a single rating curve is employed (black lines), as there is no evidence of hysteresis between the rising (filled circles) and falling (open circles) limbs of the hydrograph (see Methods). At Luang Prabang, there is likewise no evidence of hysteresis between the rising (coloured filled symbols) and falling (coloured open symbols) limbs. However, two rating functions are employed at this station, one for the pre-dam (orange coloured lines) and post-dam (green coloured lines) periods (see Methods). Source data
Extended Data Figure 3 Daily flow discharge and suspended solids load at selected Mekong River gauging stations from 1 January 1995 to 31 December 1999.
a, c, e, g, Daily simulated (Qsim) and observed (Qobs) water flows, along with the daily water flows attributable to tropical cyclones (Qsim_TC) at Luang Prabang (a), Mukdahan (c), Pakse (e) and Stung Treng (g). b, d, f, h, Daily total suspended solids load (Qs; in Mt per day) and daily suspended solids load attributable to TCs (Qs_TC; also in Mt per day) at Luang Prabang (b), Mukdahan (d), Pakse (f) and Stung Treng (h). Note that the period 1995 to 1999 encompasses the years during the 1981–2005 study period that are the most (1996) and least (1999) strongly affected by TCs. i, Goodness-of-fit measures comparing VMod simulated and observed water flows at five river gauging stations on the Lower Mekong River. Note that the goodness-of-fit metrics are all based on the mean daily flows for the full simulation period (1 May 1981 to 31 March 2005), with the exception of the mean discrepancy ratio for the annual flood peaks (Mep). The Mep metric is computed using the ratio of simulated maximum daily discharge to observed maximum daily discharge in each year of the record (1981–2004 inclusive) studied here. Source data
Extended Data Figure 4 Time series of annual suspended solids load at selected river gauging stations during 1982 to 2004.
a, Luang Prabang; b, Mukdahan; c, Pakse; d, Stung Treng. The symbols indicate the total suspended solids load (Qs; open circles) and suspended solids load attributable to TCs (Qs_TC; filled squares). Significant (P ≤ 0.05) trends as identified by Mann–Kendall analysis are indicated by the dashed lines, with the corresponding time rate of change of annual suspended solids load annotated on the plot. Source data
Extended Data Figure 5 Spatial distributions of mean annual rainfall contributed from TCs over the Mekong Basin.
a, 1981–1985; b, 1986–1990; c, 1991–1995; d, 1996–2000; e, 2001–2005. Note the pronounced declines in rainfall associated with TCs at Stung Treng and Kratie in particular.
The strike count data plotted are extracted from the IBTrACS42 database and normalized by the maximum count (199) observed in 1964. We employ strike count, rather than precipitation, data in this longer-term historical analysis because reliable precipitation data are not available outside of the 1981–2005 period that is the main focus of the study. Similarly, mean wind speed data, which in principle could be used to estimate variations in ACE as a proxy for precipitation, are available only sporadically outside of 1981–2005. In terms of strike counts, the data suggest that there is a periodicity in the long-term cyclone climatology, with the most recent data (2006–2013) having annual strike counts similar to the 1950–2013 mean of 87 ± 37. However, these data must be treated with caution since strike count data do not report the intensity or locations of cyclone tracks, both of which are important controls on the precipitation delivered to the basin by these TCs. Source data
Extended Data Figure 7 Procedures used to determine cross-section mean suspended solids concentration from acoustic Doppler current profiler data.
a, Calibration function (solid line; n = 54, r2 = 0.9306, P < 0.0001) linking the suspended solids concentration (SSC) to acoustic backscatter (ABS) for the 600 kHz (RD Instruments) acoustic Doppler current profiler (aDcp) instrument employed in this study (dashed lines indicate 95% prediction intervals). b, Example of quasi-synoptic ABS field obtained from the aDcp survey at the Kratie gauging station on 23 September 2013 (flow discharge, Q = 57,000 m3 s−1). Note that there is a small blanking distance close to the water surface and a zone of side-lobe interference near the bed (indicated by the dashed black lines) where no ABS values are returned, and the ABS values in these zones are therefore determined by interpolation. c, SSC field obtained on the basis of the ABS values in b and using the calibration function in a. Note how the locations of the nine point-based SSC estimates collected using the sampling procedure adopted at Luang Prabang and Pakse lead to a deviation of the cross-section mean SSC derived from the aDcp-estimated SSC field in c and the point-based sampling procedure. We compared 11 cross-section mean SSCs obtained using point-based versus aDcp sampling procedures at locations throughout the Mekong River south of Kratie to correct (by 26%) the consequent bias arising from cross-section averaging of point-based samples. Source data
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Darby, S., Hackney, C., Leyland, J. et al. Fluvial sediment supply to a mega-delta reduced by shifting tropical-cyclone activity. Nature 539, 276–279 (2016) doi:10.1038/nature19809
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