Effects of global irrigation on the near-surface climate

Publication Type  Journal Article
Year of Publication  2009
Authors  Sacks, W. J.; Cook, B. I.; Buenning, N.; Levis, S.; Helkowski, J. H.
Journal Title  Climate Dynamics
Volume  33
Issue  2-3
Pages  159-175
Journal Date  Aug
ISBN Number  0930-7575
Accession Number  ISI:000267103700001
Key Words  irrigation; gcm; agriculture; land management; land-cover change; water-resources; great-plains; model; temperature; simulation; impact; precipitation; colorado; moisture
Abstract  

Irrigation delivers about 2,600 km(3) of water to the land surface each year, or about 2% of annual precipitation over land. We investigated how this redistribution of water affects the global climate, focusing on its effects on near-surface temperatures. Using the Community Atmosphere Model (CAM) coupled to the Community Land Model (CLM), we compared global simulations with and without irrigation. To approximate actual irrigation amounts and locations as closely as possible, we used national-level census data of agricultural water withdrawals, disaggregated with maps of croplands, areas equipped for irrigation, and climatic water deficits. We further investigated the sensitivity of our results to the timing and spatial extent of irrigation. We found that irrigation alters climate significantly in some regions, but has a negligible effect on global-average near-surface temperatures. Irrigation cooled the northern mid-latitudes; the central and southeast United States, portions of southeast China and portions of southern and southeast Asia cooled by similar to 0.5 K averaged over the year. Much of northern Canada, on the other hand, warmed by similar to 1 K. The cooling effect of irrigation seemed to be dominated by indirect effects like an increase in cloud cover, rather than by direct evaporative cooling. The regional effects of irrigation were as large as those seen in previous studies of land cover change, showing that changes in land management can be as important as changes in land cover in terms of their climatic effects. Our results were sensitive to the area of irrigation, but were insensitive to the details of irrigation timing and delivery.

Notes  

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URL  <Go to ISI>://000267103700001
DOI  DOI 10.1007/s00382-008-0445-z