All Methods

Average GPCD in Colorado River Basin States (2015): 179

Water use data was acquired from the U.S. Geological Survey’s Water Use Data for the Nation, using the Data Retrieval Tool in R. Data and processing scripts found here.

Number of Households and Average Household Size in CRBAAS Counties (2023)

Household size and the number of households were summarized in ArcGIS pro, using the Popular Demographics in the United States – layer available in living atlas. Summaries were calculated using a CRBAS shapefile as the clipping extend and household size and number of households were summarized across CRBAS counties here.

Expected Growth in Total Population of CRBAS Counties (2020–2030)

The expected population growth indicator used the Georeferenced U.S. County-Level Population Projections, Total and by Sex, Race and Age, based on the SSps, V1 (2020-2100). 

We averaged the population growth across CRBAS counties using SSP2 for 2030.  

Hauer, M., and University, C. for I. E. S. I. N.-C.-C. (2021). Georeferenced U.S. County-Level Population Projections, Total and by Sex, Race and Age, Based on the SSPs, 2020-2100. NASA Socioeconomic Data and Applications Center (SEDAC). https://doi.org/10.7927/dv72-s254

Population of the Colorado River Basin and Areas Served 2015–2020: 43.5 Million

To calculate the CRBAS population, we utilized the POPGRID web–mapping tool, uploading the CRBAS shapefile and exporting the population count for several gridded raster data sets. Gridded data sets provide estimates, not by an administrative unit, like cities or counties, but for each pixel of the map. Depending on the data source, these pixels represent squares on the earth’s surface ranging from 10 square meters to 100 square meters. Several organizations create their own gridded data sets using a different combination of population, landcover, night-time light, development, infrastructure, topography, and climate data. The POPGRID data collaborative group hosts many of these data sets and allows researchers to query all of them by defining an area of interest. For more information on how the population estimates are made, visit POPGRID.org We utilized the WorldPop 2015 population and the WorldPop unconstrained 2020 population, and calculated the 2015–2020 growth rate

Methods PDWU1 Table1. List of the gridded population data sources used in the calculation of our population indicators.  

Note that the reported population is the population of our shapefile, or the population of the areas that contain community water systems that utilize water from the Colorado River Basin in their water supply portfolios; it should not be construed as the number of people directly using water from the Basin on a daily basis.