Hydrological threats to riparian wetlands of international importance – a global quantitative and qualitative analysis

Abstract

Abstract. Riparian wetlands have been disappearing at an accelerating rate. Their ecological integrity as well as their vital ecosystem services for humankind depend on regular patterns of inundation and drying provided by natural flow regimes. However, river hydrology has been altered worldwide. Dams cause less variable flow regimes and water abstractions decrease the amount of flow so that ecologically important flood pulses are often reduced. Given growing population pressure and projected climate change, immediate action is required. However, the implementation of counteractive measures is often a complex task. This study develops a screening tool for assessing hydrological threats to riparian wetlands on global scales. The approach is exemplified on 93 Ramsar sites, many of which are located in transboundary basins. First, the WaterGAP3 hydrological modeling framework is used to quantitatively compare current and future modified flow regimes to reference flow conditions. In our simulations current water resource management seriously impairs riparian wetland inundation at 29 % of the analyzed sites. A further 8 % experience significantly reduced flood pulses. In the future, eastern Europe, western Asia, as well as central South America could be hotspots of further flow modifications due to climate change. Second, a qualitative analysis of the 93 sites determined potential impact on overbank flows resulting from planned or proposed dam construction projects. They take place in one-third of the upstream areas and are likely to impair especially wetlands located in South America, Asia, and the Balkan Peninsula. Third, based on the existing legal/institutional framework and water resource availability upstream, further qualitative analysis evaluated the capacity to preserve overbank flows given future streamflow changes due to dam construction and climate change. Results indicate hotspots of vulnerability exist, especially in northern Africa and the Persian Gulf.

Environmental flow envelopes: quantifying global, ecosystem–threatening streamflow alterations

“…While minor flooding can still be beneficial for riverine ecosystems, extreme floods often result in adverse effects (Talbot et al, 2018) and especially floodplain ecosystems require a distinctive dry period (Hayes et al, 2018;Junk et al, 1989;Schneider et al, 2017). This dry period can be compromised by increased dry season flows, for example due to hydropower operation.…”

“…Three key drivers for the prevalence and change in EFE violations can be identified from previous research: the two main direct anthropogenic impacts of increasing water use and flow regulation, especially by dam operation (Döll et al, 2009;Graham et al, 2020;Müller Schmied et al, 2016;Schneider et al, 2017), and the indirect impact of climate change on streamflow (Arnell and Gosling, 2013;Asadieh and Krakauer, 2017;Gudmundsson et al, 2021;Moragoda and Cohen, 2020;van Vliet et al, 2013;Wanders et al, 2015). The frequent and severe EFE violations in the densely populated mid-latitudes can largely be attributed to anthropogenic impact dominating the long-term streamflow alterations (Müller Schmied et al, 2016), which is also reflected in the projected increase of water stress (use-to-availability ratio) that is driven primarily by increasing water use (Graham et al, 2020).…”

“…As the GHM outputs are generally uncertain, determining EFRs based on GHMs and hydrological EFR methods is equally uncertain. Moreover, hydrological EFR methods often set only a minimum discharge boundary, disregarding the potentially adverse effects of flows increasing significantly above natural levels especially in floodplain ecosystems (Hayes et al, 2018;Junk et al, 1989;Schneider et al, 2017;Talbot et al, 2018). Although reviews of EFs have recognised this threat of excessive flows (Acreman et al, 2014;Poff and Zimmerman, 2010;Richter, 2010), no global scale methodology exists yet to quantify it.…”

“…CC BY 4.0 License. Schneider et al, 2017), EF assessments should be able to separate violations during different flow seasons. Finally, while recent studies have shown that river flows have changed considerably due to direct human actions (Graham et al, 2020;Müller Schmied et al, 2016) and climate change (Gudmundsson et al, 2021;Moragoda and Cohen, 2020) during the past decades, no study has yet assessed the past trends in EF violations.…”

Coupling ecological water requirement to optimize water resources under changing climatic conditions

“…As indicated by the indicators of RMSE and NSE, the best-fitted association parameters could be described by the Frank copula function. Referred to both Schneider et al (2017) and Liu and Zuo (2012), daily precipitation data under the background of climate change were driven by three general circulation models, i.e., BCC-CSM1.1, BCC-CSM1.1(m), and BNU-ESM (hereafter, BC1, BC2, and BNU, respectively). Moreover, it was assumed that the above data would follow RCP 4.5 and RCP 8.5, achieving radiative forcing of 4.5 and 8.5 W m −2 , respectively, at the end of the century (Riahi et al, 2011;Thomson et al, 2011).…”