Multicompartment Depletion Factors for Water Consumption on a Global Scale

Currently, half of the global population lives in water-scarce areas, and this number is likely to increase by 2050. (1) On the one hand, humans depend on freshwater for industrial, domestic, and agricultural uses. On the other hand, human well-being also relies on healthy terrestrial and freshwater ecosystems and ecosystem services. (2) In many areas, human activities already extract freshwater at levels that put affected ecosystems at risk, and global water demand for all uses is predicted to increase by up to 30% by 2050. (3−5) Flow alteration, e.g., by dam construction and water consumption, is one persistent threat to aquatic biodiversity. (6) Water consumption has also been linked to the loss of terrestrial species, e.g., terrestrial mammals, birds, amphibians, and plants. (7,8) A sustainable management of water resources is required, calling for a balance between anthropogenic water consumption and water availability to sustain human development while safeguarding ecosystems. (9)

New integrated approaches and tools are needed to address the challenges posed by multiple, and often conflicting, water needs for humans and ecosystems. (10) Several tools and methods have already been proposed to tackle these issues, including water footprinting, (9,11) planetary boundaries, (12) integrated water resource management, (13) life cycle assessment (LCA), (14−16) and environmentally-extended multi-regional input–output analysis. (17) The integrated nature of hydrological systems requires that the assessment of environmental impacts of water consumption differentiates between water compartments to reflect distributions and renewability levels among water sources. (18) Different compartments interact with varying strengths and over a wide range of geographical and temporal scales with other components of the Earth system, such as the atmosphere, biosphere, and lithosphere. Evaluating the ecological impacts of water management decisions, therefore, requires accounting for the hydrologic processes that determine the relationships between surface and subsurface waters, as surface water, soil water, and groundwater influence one another. (19) Existing life cycle impact assessment (LCIA) models for freshwater consumption characterize the associated damages to ecosystems and human health. (8,14,20−24) However, the interlinkages across water compartments are rarely considered, except for a few studies modeling the recycling and transfer of evapotranspiration and LCIA models quantifying potential impacts on ecosystems...

Figure 1. Cause-effect chain linking water consumption to hydrological indicators and subsequently to ecosystems and freshwater natural resources.

Figure 2. Global maps of water consumption change and resulting depletion factors for streamflow, groundwater compartment storage, soil moisture, and evapotranspiration for 8664 river basins from 1960 to 2000. The effect of water consumption on the different depletion factors is split between positive (left) and negative (right) values for simplicity of representation.

aPositive and negative depletion factors are reported in blue and red, respectively. Consumption change and average groundwater–surface water consumption ratio are reported in parenthesis after the cumulated consumption. The consumption change is relative to the mean value over the period 1960–2000.