Research Article
Climate-induced trends in global riverine water discharge and suspended sediment dynamics in the 21st century

https://doi.org/10.1016/j.gloplacha.2020.103199Get rights and content

Highlights

  • Future climate change considerably impacts global river water and sediment fluxes.

  • Global warming increases the magnitudes and variability of discharge and sediment.

  • More rivers will experience extreme changes in both variables with climate warming.

  • Predicted trends in precipitation mainly drive changes in sediment and discharge.

Abstract

Anthropogenic climate change, particularly through increased greenhouse gas (GHG) emissions, is projected to impact 21st century precipitation distribution, altering fluvial processes such as riverine water discharge and sediment dynamics, worldwide. Changes in fluvial water and sediment discharges can have profound impacts on the functioning and connectivity of earth's natural systems. In this paper, we study the natural sensitivity of water discharge and suspended sediment fluxes in large global river systems to predicted climate change in the 21st century. A global-scale hydro-geomorphic model (WBMsed) was forced with precipitation and temperature projections generated by five General Circulation Models (GCMs), each driven by four Representative Concentration Pathways (RCPs). Anthropogenic drivers were excluded from the simulations in order to isolate the signal of 21st century climate change. The results, based on an ensemble of model outputs, revealed that global river discharge and sediment dynamics are highly sensitive to anthropogenic climate change in the 21st century. Increasing global warming will lead to more extreme changes and greater rates of changes (increasing or decreasing) in both variables. Despite substantial regional heterogeneity, a global net increase is projected for both natural river discharge and sediment flux toward the end of the 21st century under all climate change scenarios. These increases are larger with increasing levels of atmospheric warming. At the end of this century, projected climate changes under RCP 2.6, 4.5, 6.0 and 8.5 scenarios, will lead to 2%, 6%, 7.5% and 11% increases respectively in mean global river discharge relative to the 1950–2005 period, while mean global suspended sediment flux will show 11%, 15%, 14% and 16.4% increases under pristine conditions. In addition to magnitudes, inter-annual variability also increases with increasing warming. Changes in sediment flux closely follow the patterns predicted for discharge, and are mostly driven by climate warming-induced spatial and temporal variation in precipitation. However, the relationship between precipitation, discharge and sediment flux was found to be non-linear both in space and time, demonstrating the utility of explicit modeling of both hydrology and geomorphology.

Introduction

Human influence on the climate through anthropogenic greenhouse gas (GHG) emissions is leading to warming of the global climate system (IPCC, 2014). Climate warming has caused substantial changes in the hydrological cycle, altering the quantity and quality of available water resources in many regions worldwide (Bates et al., 2008). This has placed increased attention on the future of global rivers, especially how changes in climate will induce behavioral changes in fluvial systems (Bates et al., 2008; Syvitski et al., 2003; Walling, 2009). A comprehensive understanding of the response of fluvial systems to future changes in climate warrants detailed analysis of future riverine water discharge and sediment fluxes (Shrestha et al., 2016). Sediment transport by rivers plays an essential role in the functioning and connectivity of the earth's natural systems, by directly influencing ecohydrological, biogeochemical and geomorphological processes (Vörösmarty et al., 2003; Walling and Fang, 2003). It serves as an important sensitive indicator of changes in the Earth's processes (Fryirs, 2013; Walling, 2009), and is essential for studying nutrient cycles, contaminant pathways, biodiversity and habitat conditions in riverine, coastal and marine ecosystems (Mukundan et al., 2013; Syvitski and Milliman, 2007; Walling, 2009). Sediments are responsible for structuring landscape features such as deltas (Darby et al., 2015; Dunn et al., 2019) and controlling channel geometry and morphology (Pelletier, 2012; Vercruysse et al., 2017). In addition to the key role in natural planetary functions, sediment dynamics has important engineering and socio-economic implications on, e.g., dam sustainability, flood hazards, and water quality (Vercruysse et al., 2017). Although there is extensive literature with regard to estimation of sediment fluxes (e.g. Pelletier, 2012; Syvitski and Milliman, 2007; Syvitski et al., 2003; Walling and Fang, 2003), simulating global riverine sediment fluxes still remains challenging owing to the multiscale nature (Cohen et al., 2014; Pelletier, 2012; Vercruysse et al., 2017) and the non-linear relationship of the processes involved (Coulthard et al., 2012; Fryirs, 2013).

A major factor affecting changes in sediment transport and river discharge is climate (Aerts et al., 2006; Haddeland et al., 2014; Syvitski, 2003a; Syvitski, 2003b). Future changes in climate, particularly rises in temperature driven by increased GHG emissions, are projected to considerably alter 21st century precipitation intensity and distribution (IPCC, 2014; Lu et al., 2013; Oki and Kanae, 2006; Pendergrass et al., 2017). Research has shown that moderate changes in average climate conditions (i.e. changes of 1–2 °C, 10–20% precipitation) can lead to substantial changes in rivers including sediment yield (Knox, 1993; see Syvitski, 2003b). Not only average climate conditions, but also projected increases in extreme events due to climate change can have profound and complex impacts on hydrological responses of a catchment (Fryirs, 2013).

Human interferences on hydrological systems e.g., damming, soil erosion and conservation measures also have substantial influences on rivers (Walling, 2009; Wang et al., 2011; Syvitski et al., 2005). The increasing impacts of both human activities and climate change necessitate the need to identify and quantify the impacts from individual drivers on fluvial water and sediment discharges (Yang et al., 2015). Isolating the effects of changing climate as one of the primary drivers of changes in fluvial systems can facilitate more informed decision making with regard to human activities affecting hydrological systems. However it is difficult, in most cases, to disentangle the signal of climate from other human impacts (Lu et al., 2013; Walling, 2009).

A number of studies have been carried out to explore the recent trends in discharge and suspended sediment loads in global rivers at a range of scales (e.g. Cohen et al., 2014; Syvitski, 2002; Syvitski et al., 2003; Walling and Fang, 2003; Wang et al., 2011). Basin scale studies provide evidence of marked changes in the sediment loads and water discharge in recent years (Dai et al., 2009; López and Torregroza, 2017; Walling, 2009). In many instances, these changes are predicted based on the interactions between climate change and human impacts (Dai et al., 2009; Syvitski and Milliman, 2007; Syvitski et al., 2003; Walling and Fang, 2003; Wang et al., 2011). Although there is a wealth of literature related to the effects of GHG-induced global warming on future water discharge of rivers at a global scale (e.g. Milly et al., 2005; Nakaegawa et al., 2013; Nijssen et al., 2001; Sperna Weiland et al., 2012), assessments of sediment flux in response to climate change are mostly at the river catchment scale (Coulthard et al., 2012; Darby et al., 2015; Rodríguez-Blanco et al., 2016; Zhu et al., 2008). More recent studies such as Dunn et al. (2019) and Nienhuis et al. (2020) looked at changes in sediment delivery to river deltas worldwide and the different drivers responsible for these changes.

This paper is focused on providing a comprehensive and spatially explicit analysis of the natural sensitivity of global riverine water discharge and suspended sediment fluxes to future climate change trajectories. In order to achieve this objective, the study was conducted under conditions that mimic a pristine world without anthropogenic activities. This gives the opportunity to identify the direction and relative strength of the unmixed signal of GHG-induced climate change in the 21st century on global riverine fluxes, for different climate change scenarios. Existing anthropogenic activities (e.g. dams, land management practices) may hinder this signal and counter-balance the changes predicted based only on climate change.

Section snippets

Model description

Global riverine water discharge and suspended sediment fluxes were simulated using the spatially and temporally explicit global riverine sediment flux model WBMsed v2.0 (Cohen et al., 2014). WBMsed is an extension of the WBMplus global hydrology model (Wisser et al., 2010; see Cohen et al., 2013). A comprehensive description of the model infrastructure and input parameters can be found in Cohen et al. (2013 and 2014). WBMsed employs the BQART model (Syvitski and Milliman, 2007) as its governing

Model validation

Cohen et al., 2013, Cohen et al., 2014 evaluated the WBMsed model predictions of long-term averaged suspended sediment flux and water discharge (using observed climate inputs) and found a correlation of R2 = 0.66 to observed sediment flux and R2 = 0.70 to water discharge for 95 global sites. A stronger correlation was found to observed sediment flux for 11 USGS sites (R2 = 0.94). In this study, the model's forecasting capability using GCM forcings was assessed based on the ensemble hindcast

Discussion

Due to the different structures and parameters used in GCMs, projected future changes in temperature and precipitation have large spatial and temporal uncertainties even for the same radiative forcing levels (Cai et al., 2009; Knutti and Sedláček, 2013). Therefore, studies that investigate climate change responses of fluvial systems show varying degrees and directions of changes over the 21st century (Arnell, 2003; Haddeland et al., 2014; Hagemann et al., 2013; Schewe et al., 2013; van Vliet et

Conclusion

In order to isolate the signal of projected future climate change on global riverine water discharge and suspended sediment fluxes in the 21st century under pristine conditions, a numerical model (WBMsed) was forced with precipitation and temperature projections from five GCMs each driven by four RCPs. The results, based on an ensemble of model outputs, revealed that natural global river discharge and sediment fluxes are highly sensitive to anthropogenic climate change in the 21st century.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We express our gratitude to Dr. Hamid Moradkhani and Dr. Sarah Praskievicz for their constructive comments, and the anonymous reviewers for their valuable suggestions that helped us to improve the quality of this paper. This research was partly funded by the University Corporation for Atmospheric Research (UCAR), United States grant number SUBAWD000837.

References (70)

  • J. Syvitski et al.

    River temperature and the thermal-dynamic transport of sediment

    Glob. Planet. Chang.

    (2019)
  • M.T. van Vliet et al.

    Global river discharge and water temperature under climate change

    Glob. Environ. Chang.

    (2013)
  • K. Vercruysse et al.

    Suspended sediment transport dynamics in rivers: multi-scale drivers of temporal variation

    Earth Sci. Rev.

    (2017)
  • C.J. Vörösmarty et al.

    Anthropogenic sediment retention: major global impact from registered river impoundments

    Glob. Planet. Chang.

    (2003)
  • D.E. Walling et al.

    Recent trends in the suspended sediment loads of the world's rivers

    Glob. Planet. Chang.

    (2003)
  • H. Wang et al.

    Recent changes of sediment flux to the western Pacific Ocean from major rivers in East and Southeast Asia

    Earth Sci. Rev.

    (2011)
  • Y.M. Zhu et al.

    Sediment flux sensitivity to climate change: a case study in the Longchuanjiang catchment of the upper Yangtze River, China

    Glob. Planet. Chang.

    (2008)
  • J.C.J.H. Aerts et al.

    Sensitivity of global river discharges under Holocene and future climate conditions

    Geophys. Res. Lett.

    (2006)
  • N.W. Arnell

    Effects of IPCC SRES* emissions scenarios on river runoff: a global perspective

    Hydrol. Earth Syst. Sci. Discuss.

    (2003)
  • C. Bjørnæs

    A Guide to Representative Concentration Pathways

    (2013)
  • X. Cai et al.

    Assessing the regional variability of GCM simulations

    Geophys. Res. Lett.

    (2009)
  • T.J. Coulthard et al.

    Using the UKCP09 probabilistic scenarios to model the amplified impact of climate change on drainage basin sediment yield

    Hydrol. Earth Syst. Sci.

    (2012)
  • A. Dai et al.

    Surface observed global land precipitation variations during 1900–88

    J. Clim.

    (1997)
  • A. Dai et al.

    Changes in continental freshwater discharge from 1948 to 2004

    J. Clim.

    (2009)
  • S.E. Darby et al.

    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

    (2015)
  • F.E. Dunn et al.

    Projections of declining fluvial sediment delivery to major deltas worldwide in response to climate change and anthropogenic stress

    Environ. Res. Lett.

    (2019)
  • K. Frieler et al.

    Assessing the impacts of 1.5 C global warming–simulation protocol of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2b)

    Geosci. Model Dev.

    (2017)
  • K. Fryirs

    (Dis) Connectivity in catchment sediment cascades: a fresh look at the sediment delivery problem

    Earth Surf. Process. Landf.

    (2013)
  • R.J. Haarsma et al.

    Sahel rainfall variability and response to greenhouse warming

    Geophys. Res. Lett.

    (2005)
  • I. Haddeland et al.

    Global water resources affected by human interventions and climate change

    Proc. Natl. Acad. Sci.

    (2014)
  • S. Hagemann et al.

    Climate change impact on available water resources obtained using multiple global climate and hydrology models

    Earth Syst. Dyn.

    (2013)
  • F.F. Hattermann et al.

    Sources of uncertainty in hydrological climate impact assessment: a cross-scale study

    Environ. Res. Lett.

    (2018)
  • S. Hempel et al.

    A trend-preserving bias correction–the ISI-MIP approach

    Earth Syst. Dyn.

    (2013)
  • Y. Hirabayashi et al.

    Global projections of changing risks of floods and droughts in a changing climate

    Hydrol. Sci. J.

    (2008)
  • Cited by (23)

    • Evolution patterns and spatial sources of water and sediment discharge over the last 70 years in the Yellow River, China: A case study in the Ningxia Reach

      2022, Science of the Total Environment
      Citation Excerpt :

      Notably, changes in water and sediment discharge have important impacts on social development, as these processes determine the formulation of river governance strategies and may even restrict sustainable development (Syvitski, 2003). Therefore, the changes in river water and sediment discharge and their influencing factors are essential issues that need to be considered (Buendia et al., 2016a; Burt et al., 2016; Chen et al., 2017; Moragoda and Cohen, 2020). The Yellow River, the second-largest river in China, is seriously affected by anthropogenic activities (Wang et al., 2015).

    • Drivers and extent of surface water occurrence in the Selenga River Delta, Russia

      2021, Journal of Hydrology: Regional Studies
      Citation Excerpt :

      However, this may not be the case for the SRD under the period of study. Chalov et al. (2015) found that during 1983–2011, the correlation factor between the surface runoff and the suspended sediment concentration was only 0.16 (Chalov et al., 2015; Moragoda and Cohen, 2020). Furthermore, no significant overbank flow has been observed in the flood season after 2011 (Chalov et al., 2015), leading to no flooding from bank overflow, reducing an even stronger relationship between the runoff and water occurrence.

    View all citing articles on Scopus
    View full text