Freshwater scarcity is increasingly perceived as a global systemic risk. Previous global water scarcity assessments, measuring water scarcity annually, have underestimated experienced water scarcity by failing to capture the seasonal fluctuations in water consumption and availability. We assess blue water scarcity globally at a high spatial resolution on a monthly basis. We find that two-thirds of the global population (4.0 billion people) live under conditions of severe water scarcity at least 1 month of the year. Nearly half of those people live in India and China. Half a billion people in the world face severe water scarcity all year round. Putting caps to water consumption by river basin, increasing water-use efficiencies, and better sharing of the limited freshwater resources will be key in reducing the threat posed by water scarcity on biodiversity and human welfare.

/pdf/four-billion-people-facing-severe-water-scarcity-4oc8947upp.pdf

Four billion people facing severe water scarcity

Summary
1. In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management.

2. For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A ‘qualitative’ or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values.

3. Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel.

4. Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response; however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration.

5. New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration–ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration.

https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/deltaflow/docs/exhibits/swrcb/swrcb_poff2010_2.pdf

Ecological responses to altered flow regimes: a literature review to inform the science and management of environmental flows

This manual presents a scientifically rigorous method to help companies understand their dependency and impact on global water resources, and offers guidance on response strategies that conserve water for industry, communities, and nature. It contains the global standard for water footprint assessment as developed and maintained by the Water Footprint Network. It covers a comprehensive set of definitions and methods for water footprint accounting. It shows how water footprints are calculated for individual processes and products, as well as for consumers, nations, and businesses. It also includes methods for water footprint sustainability assessment and a library of water footprint response options. The water footprint of a product is the volume of freshwater used to produce the product, measured over the fully supply chain. It is a multidimensional indicator, showing water consumption volumes by source and polluted volumes by type of pollution; all components of a total water footprint are specified geographically and temporally.

/pdf/the-water-footprint-assessment-manual-setting-the-global-32uctgx0m9.pdf

The Water Footprint Assessment Manual: Setting the Global Standard

Despite the recognized importance of reservoirs and dams, global datasets describing their characteristics and geographical distribution are largely incomplete. To enable advanced assessments of th ...

/pdf/high-resolution-mapping-of-the-world-s-reservoirs-and-dams-153xoufrow.pdf

High‐resolution mapping of the world's reservoirs and dams for sustainable river‐flow management

SUMMARY 1. The flow regime is a primary determinant of the structure and function of aquatic and riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine ecosystems on a global scale, and the pace and intensity of human development greatly exceeds the ability of scientists to assess the effects on a river-by-river basis. Current scientific understanding of hydrologic controls on riverine ecosystems and experience gained from individual river studies support development of environmental flow standards at the regional scale. 2. This paper presents a consensus view from a group of international scientists on a new framework for assessing environmental flow needs for many streams and rivers simultaneously to foster development and implementation of environmental flow standards at the regional scale. This framework, the ecological limits of hydrologic alteration (ELOHA), is a synthesis of a number of existing hydrologic techniques and environmental flow methods that are currently being used to various degrees and that can support comprehensive regional flow management. The flexible approach allows

/pdf/the-ecological-limits-of-hydrologic-alteration-eloha-a-new-3424c2qgtj.pdf

The ecological limits of hydrologic alteration (ELOHA): a new framework for developing regional environmental flow standards

This manual is a user’s guide to four computer software tools that have been developed for the Hydroecological Integrity Assessment Process. The Hydroecological Integrity Assessment Process recognizes that streamflow is strongly related to many critical physiochemical components of rivers, such as dissolved oxygen, channel geomorphology, and water temperature, and can be considered a “master variable” that limits the disturbance, abundance, and diversity of many aquatic plant and animal species. Applying the Hydroecological Integrity Assessment Process involves four steps: (1) a hydrologic classification of relatively unmodified streams in a geographic area using long-term gage records and 171 ecologically relevant indices; (2) the identification of statistically significant, nonredundant, hydroecologically relevant indices associated with the five major flow components for each stream class; and (3) the development of a stream-classification tool and a hydrologic assessment tool. Four computer software tools have been developed. • The Hydrologic Index Tool calculates 171 biologically relevant hydrologic indices using daily and peak flow records. The indices are then used for a regional (State) stream classification analysis. The program is designed to import U.S. Geological Survey mean daily and peak flow discharges from the National Water Information System databases. • The National Hydrologic Assessment Tool is based on a hydrologic classification of streams which used 420 gaging stations across the contiguous United States. The National Hydrologic Assessment Tool has six stream classes identified. The program is used to establish a hydrologic baseline (reference time period), to establish environmental flow standards, and to evaluate past and proposed hydrologic modification. This is accomplished by using flow statistics, trend analysis, and 10 primary stream class specific indices that address the five major components of flow. • A New Jersey stream classification tool classifies any stream within the State into one of the four stream types found in the State. The four classes of streams identified in New Jersey are characterized by the relative degree of skewness of daily flows (low = stable flow, high = flashy flow) and frequency of low-flow events (low = high base flow; high = low base flow). Thus, streams belonging to stream class A are semiflashy with moderately low baseflow, class B streams are stable with high base flow, class C streams are moderately stable with a moderately high base flow, and class D streams are flashy with a low base flow. • The New Jersey Hydrologic Assessment Tool is used to establish a hydrologic baseline (reference time period), establish environmental flow standards, and evaluate past and proposed hydrologic modifications of streams in New Jersey. This is accomplished by using flow statistics, trend analysis, and 10 primary stream class specific indices that address the five major components of flow.

/pdf/users-manual-for-the-hydroecological-integrity-assessment-1xoqbxuerm.pdf

Users' manual for the Hydroecological Integrity Assessment Process software (including the New Jersey Assessment Tools)

..........................................................................................................................................................

/pdf/development-of-the-hydroecological-integrity-assessment-51hukxnxp8.pdf

Development of the Hydroecological Integrity Assessment Process for Determining Environmental Flows for New Jersey Streams

/pdf/application-of-the-hydroecological-integrity-assessment-47e7ayter9.pdf

James A. Henriksen

Papers

The ecological limits of hydrologic alteration (ELOHA): a new framework for developing regional environmental flow standards

Users' manual for the Hydroecological Integrity Assessment Process software (including the New Jersey Assessment Tools)

Development of the Hydroecological Integrity Assessment Process for Determining Environmental Flows for New Jersey Streams

Application of the Hydroecological Integrity Assessment Process for Missouri Streams