Collection Information: Ecosystem Demography Model (ED)

The Global Demographic Data collection holds global gridded data products describing demographic information and water demand in relation to population data.

Country-level urban, rural and total population estimate data from World Resources Institute (WRI) for the years 1985, 1995, and 2025 were gridded by the University of New Hampshire’s Water Systems Analysis Group using methods outlined in Vörösmarty et al. (2000) for use in estimating global water resources based on climate and population changes.

"The future adequacy of freshwater resources is difficult to assess, owing to a complex and rapidly changing geography of water supply and use. Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrates that (i) a large proportion of the world’s population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question" (Vörösmarty et al., 2000).

Currently available are five relative water demand (RWD) fraction data sets/ maps, produced by Vörösmarty et al. in their analysis of future water resources. The relative water demand is defined to be the total volume of water used either domestically, industrially or agriculturally (DIA) divided by the water discharge (Q). "Values … of .2 to .4 indicate medium to high stress." (see Vörösmarty et al., 2000) This analysis deals only with sustainable water sources, and does not look at nonsustainable water sources, such a ground water mining. The RWD is computed on a .5 by .5 degree grid for two sentinel years: 1985 and 2025, which are two of the data sets. The ratio of the RWD for these two years provides a measure of change under scenarios of climate change only, population change only and the combination of climate change and population to produce the other three datasets. The ratio RWD values is relative to the RWD in the base year, 1985.

Nine gridded population data sets/maps are also available; these data were produced and used by Vörösmarty et al. in their analysis of future water resources. Three different annual snapshots (1985, 1995, 2025) of population are provided for urban, rural and total population. Water demand data will also be provided through EOS-WEBSTER in the near future, and was determined using the population data and per capita use statistics (see Vörösmarty et al., 2000).

Data Sets

Variables

Data Range

Water Demand

a) Relative Water Demand
b) Ratio of Relative Water Demand

.2 -.4 is stress
>20% is significant

Annual Population Estimates

a) Population (# people/grid cell)

0 – ~33 million/grid cell
(varies by holding)

These data are gridded in the geographic projection with 0.5 degree by 0.5 degree cell sizes. The data are bounded by 83.0 N to 55.5 S latitude, and by 180.0 W to 180.0 E longitude. For water demand, there are two snapshot years 1985 and 2025. There are three datasets which are the difference in water demand between those years under different scenarios. For the population data, the data represent annual snapshots for 1985, 1995, and 2025 respectively, and are based on the World Resources Institute’s country-level population data for these years.

The full dataset contains 720 cells in the x-dimension (longitude) and 277 cells in the y-dimension (latitude) of long integer data. The fill value for missing data is –9999 and non-land/ocean grid cells are represented with a population value of 0. Data format, x/y grid dimension, and absolute range of the data values may vary depending on the output format and the spatial region you select when ordering the data.

Relative water demand (RWD) is defined to be the total volume of water used either domestically, industrially or agriculturally (DIA) divided by the water discharge (Q). "Values … of .2 to .4 indicate medium to high stress."

A predictive year of 2025 is modeled for water demand based on three different scenarios: population change under current climate, climate change under constant population and water withdrawals, and the combination of climate change and population change. The ratio of the RWD (relative water demand) over RWD in 1985 as a base year under the three different scenarios is the "difference" holdings. The range of values .8 to 1.2 were deemed to be less significant, but those .8 or greater than 1.2 were substantial changes to the system.

Vörösmarty, C.J., P. Green, J. Salisbury, and R. Lammers. 2000. Global water resources: vulnerability from climate change and population growth. Science: 14 July 2000, Vol. 289, pp. 284-288.

Water Systems Analysis Group, Complex Systems Research Center, Institute for the Study of Earth, Oceans, and Space, Morse Hall, University of New Hampshire, Durham, New Hampshire, USA. Ph: 603.862.1792, Fax: 603.862.0188.