G1 DESCRIPTION:

Gridded field of irrigation withdrawals for 2000 (in millions of cubic meters per year) at 30 minute (lattitude by longitude) resolution (Vorosmarty et al., 2005). Country-level irrigation withdrawals per capita (World Resources Institute, http://earthtrends.wri.org/) were multiplied by country-level population to estimate irrigation withdrawals for each country. Country-level irrigation withdrawals were distributed over irrigated lands (aggregated from Doll and Siebert, 2000) prorated on estimated irrigation need. Irrigation need was computed as the difference between potential evapotranspiration (PET, which represents the crop water requirements under optimal conditions) and actual evapotranspiration (AET). PET was estimated using the physically-based function of Shuttleworth and Wallace (1985), which is a modification of the standard Penman-Monteith PET equation. AET was estimated by the Water Balance Model (Vorosmarty et al., 1998).

DOWNLOADABLE FILES:

(G1) ag_2000_mlnm3.asc = Gridded field of irrigation withdrawals for 2000 (in millions of cubic meters per year for each irrigated grid cell) at 30 minute (latitude by longitude) resolution. Primary source: (Vorosmarty et al., 2005).

REFERENCES:

Döll, P., Siebert, S. 2000. A digital global map of irrigated areas. ICID Journal, 49(2), 55-66.

Shuttleworth, W. J. and J. S. Wallace. 1985. Evaporation from sparse crops: an energy combination theory, Quarterly J. R. Meteorol. Soc., 111: 839-855.

Vörösmarty, C.J., C. Leveque, C. Revenga (Convening Lead Authors). 2005. Chapter 7: Fresh Water. In: Millennium Ecosystem Assessment, Volume 1: Conditions and Trends Working Group Report, (with R. Bos, C. Caudill, J. Chilton, E. M. Douglas, M. Meybeck, D. Prager, P. Balvanera, S. Barker, M. Maas, C. Nilsson, T.Oki, C. A. Reidy). Island Press. In press.

Vörösmarty, C. J., C. A. Federer, and A. L. Schloss. 1998. Potential evapotranspiration functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling, Journal of Hydrology, 207: 147-169.

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