Poor correlation between large-scale environmental flows violations and global freshwater biodiversity: implications for water resource management and the water planetary boundary

The relationship between streamflow alterations and, respectively, EF violations, and freshwater biodiversity is well established at the scale of stream reaches or small basins (~<100 km²). However, it is unclear if this relationship is robust at larger scales even though there are large-scale initiatives to legalize the EF requirement and EFs have been used in assessing a planetary boundary for freshwater.

Therefore, this study intends to evaluate the relationship between EF violation and freshwater biodiversity at large basin scale (median area = 19,600 km2), globally-aggregated scales, and at freshwater ecoregions, and test the prevailing assumption of scalability of this relationship. Four EF violation indices (severity, frequency, the probability to shift to violated state, and probability to stay violated) and nine independent freshwater biodiversity indicators (calculated from observed biota data except one empirically derived from streamflow deviation) were used for correlation analysis.