Globally widespread and increasing violations of environmental flow envelopes

[摘要] Human actions and climate change have drastically alteredriver flows across the world, resulting in adverse effects on riverineecosystems. Environmental flows (EFs) have emerged as a prominent tool forsafeguarding the riverine ecosystems, but at the global scale, theassessment of EFs is associated with high uncertainty related to thehydrological data and EF methods employed. Here, we present a novel,in-depth global EF assessment using environmental flow envelopes (EFEs).Sub-basin-specific EFEs are determined for approximately 4400 sub-basins ata monthly time resolution, and their derivation considers the methodologicaluncertainties related to global-scale EF studies. In addition to a lowerbound of discharge based on existing EF methods, we introduce an upper boundof discharge in the EFE. This upper bound enables areas to be identified wherestreamflow has substantially increased above natural levels. Further,instead of only showing whether EFs are violated over a time period, wequantify, for the first time, the frequency, severity, and trends of EFEviolations during the recent historical period. Discharge was derived from global hydrological model outputs from the ISIMIP2b ensemble. We use pre-industrial (1801–1860) quasi-natural dischargetogether with a suite of hydrological EF methods to estimate the EFEs. Wethen compare the EFEs with recent historical (1976–2005) discharge to assessthe violations of the EFE. These violations most commonly manifestas insufficient streamflow during the low-flow season, with fewerviolations during the intermediate-flow season, and only a few violationsduring the high-flow season. The EFE violations are widespread and occurin half of the sub-basins of the world during more than 5 % of the monthsbetween 1976 and 2005, which is double compared with the pre-industrialperiod. The trends in EFE violations have mainly been increasing, which willlikely continue in the future with the projected hydroclimatic changes andincreases in anthropogenic water use. Indications of increased upper extremestreamflow through EFE upper bound violations are relatively scarce anddispersed. Although local fine-tuning is necessary for practicalapplications, and further research on the coupling between quantitativedischarge and riverine ecosystem responses at the global scale is required,the EFEs provide a quick and globally robust way of determiningenvironmental flow allocations at the sub-basin scale to inform globalresearch and policies on water resources management.

[学科分类] 妇产科学