Illustrating a new global-scale approach to estimating potential reduction in fish species richness due to flow alteration

Abstract

Abstract. Changes in river discharge due to human activities and climate change would affect the sustainability of freshwater ecosystems. To globally assess how changes in river discharge will affect the future status of freshwater ecosystems, global-scale hydrological simulations need to be connected with a model to estimate the durability of freshwater ecosystems. However, the development of this specific modelling combination for the global scale is still in its infancy. In this study, two statistical methods are introduced to link flow regimes to fish species richness (FSR): one is based on a linear relationship between FSR and mean river discharge (hereafter, FSR-MAD method), and the other is based on a multi-linear relationship between FSR and ecologically relevant flow indices involving several other flow characteristics and mean river discharge (FSR-FLVAR method). The FSR-MAD method has been used previously in global simulation studies. The FSR-FLVAR method is newly introduced here. These statistical methods for estimating FSR were combined with a set of global river discharge simulations to evaluate the potential impact of climate-change-induced flow alterations on FSR changes. Generally, future reductions in FSR with the FSR-FLVAR method are greater and much more scattered than with the FSR-MAD method. In arid regions, both methods indicate reductions in FSR because mean discharge is projected to decrease from past to future, although the magnitude of reductions in FSR is different between the two methods. In contrast, in heavy-snow regions a large reduction in FSR is shown by the FSR-FLVAR method due to increases in the frequency of low and high flows. Although further research is clearly needed to conclude which method is more appropriate, this study demonstrates that the FSR-FLVAR method could produce considerably different results when assessing the global role of flow alterations in changing freshwater ecosystems.

An assessment of global net irrigation water requirements from various water supply sources to sustain irrigation: rivers and reservoirs (1960–2050)

“…In the H08 model, such values have been estimated, but without considering explicit linkages to freshwater ecosystem structure and function. Yoshikawa et al (2014) suggested that there is a strong need to find ways to incorporate this linkage to more adequately determine environmental flows for each region at a global scale. Incorporating these factors into future simulations in the H08 model, while challenging, is critically important.…”

Authors response

“…Assigned values can be expressed in either monetary or nonmonetary terms, and are relevant to economic and psychology approaches. In a social-science context, assigned values have been quantitatively measured using a variety of techniques, including survey and interview approaches with the help of psychometric scales used in psychology (Bengston, 1994), social experiments in behavioral economics (Janssen et al, 2014;Yu et al, 2016) and content analysis (Seymour et al, 2010;Bark et al, 2016a;Xu and Bengston, 1997;Wei et al, 2017).…”

Moving sociohydrology forward: a synthesis across studies

“…Thus, a sociohydrologic relationship may arise directly -for example, a direct relationship between reduced well-being and water scarcity (Srinivasan, 2015) -or indirectly, for example, a relationship between economic output from a fishery and water quality. Changes in flow regimes can affect fish species richness (Yoshikawa et al, 2014), and regions dependent on fishing may become sensitive to hydrologic change through the impact on fish rather than water quantity. Fundamentally, the presence of multiple pathways for coupling between water and society, and the potential for these pathways to occur indirectly and to be influenced by other components of the system, suggests the study of sociohydrology is prototypical of complex systems science.…”