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Why a water census
Growing demand and competition for limited regional water make it hard to ensure enough for both people and ecosystems. So the USGS made a National Water Census (NWC) one of its six core science directions for 2007–17, and in 2009 the SECURE Water Act directed it to build a national water availability and use assessment — updating the last national assessments (from 1968 and 1978) and improving forecasts.
The census looks at how changes in land use, water use and climate affect the amount and distribution of water, water quality, and human and aquatic ecosystem health. It feeds the Interior Department's WaterSMART initiative for a sustainable national water supply, and the USGS works with federal, regional and local partners to set its priorities.
Three goals
- Nationally consistent data on the major parts of the water budget, and on water use.
- Better understanding of the flows ecosystems need.
- Assessments of river basins where competition for water is intense.
Later goals include linking water supply and quality (including the use of impaired water), studying more basins, and better uncertainty analysis. Much of the information comes from models and statistical estimates; the National Water Census Data Portal lets users map, download and analyze it.
The parts of a simple water budget for a watershed. USGS, modified from Healy and others (2007).
A national water budget
Consistent data for many water-budget components don't yet exist, regionally or nationally. The NWC's unifying aim is estimates at consistent basin and monthly scales, built up through:
Topical studies of streamflow, groundwater, precipitation, evapotranspiration and water use — plus ecological flows, the link between water availability and healthy ecosystems. Each develops new methods, makes data more accessible, and measures and reduces uncertainty, supporting local and regional agencies and research on national and global water cycles.
Geographic Focus Area studies — regional assessments where water needs for drinking, irrigation, energy, industry or ecosystems outpace supply. They test ways to measure the water budget and apply them to real management problems, and "ground-truth" national methods with local information.
Geographic Focus Area studies: the first three (blue) and three more starting in October 2015 (orange). USGS.
| Focus Area | Status (2015) | Work |
|---|---|---|
| Apalachicola–Chattahoochee–Flint, Colorado and Delaware river basins | under way | water-use databases, including consumptive use and trends; estimating streamflow at ungaged streams; linking surface-water and groundwater models; decision tools and ecological models predicting how fish and mussels respond to climate, land use and water use |
| Red River, Rio Grande and Coastal Basins of the Carolinas | starting October 2015 | effects of dust on snow; refining and coupling groundwater and surface-water models; methods to evaluate irrigation |
Sources
Based on "Progress Toward a National Water Census," U.S. Geological Survey fact sheet; a work of the United States government in the public domain. The opening, the water-budget diagram and the map are taken from the fact sheet's PDF.
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