Irrigation in the climate system: transient and equilibrium responses
Event details
| Date | 28.02.2011 |
| Hour | 16:15 |
| Speaker | Dr Ben COOK; NASA Goddard Institute for Space Studies New York, USA |
| Location |
GR B3 30
|
| Category | Conferences - Seminars |
Various studies have documented the effects of modern-day irrigation on regional and global climate, but few have considered 1) the time-varying impact of steadily increasing irrigation rates on climate during the twentieth century or 2) how the effect of irrigation on surface climate will change with increased greenhouse gas (GHG) forcing. To address these questions, we use spatially explicit estimates of modern and historical irrigation, in combination with historical and increased GHG forcings, to force several transient and equilibrium runs with an atmosphere general circulation model. In our historical simulations, irrigation early in the twentieth century is primarily localized over southern and eastern Asia, leading to significant cooling in boreal summer (June-August) over these regions. This cooling spreads and intensifies by century's end, following the rapid expansion of irrigation over North America, Europe, and Asia. Irrigation also leads to boreal winter (December-February) warming over parts of North America and Asia in the latter part of the century, through enhanced downward longwave fluxes from increased near-surface humidity. Precipitation increases occur primarily downwind of the major irrigation areas, although precipitation in parts of India decreases due to a weaker summer monsoon. Irrigation begins to significantly reduce temperatures and temperature trends during boreal summer over the Northern Hemisphere midlatitudes and tropics beginning around 1950; significant increases in precipitation occur in these same latitude bands. For the modern equilibrium scenario, the cooling is largest over North America, India, the Middle East, and East Asia. Under increased GHG forcing, this cooling effect largely disappears over North America, remains relatively unchanged over India, and intensifies over parts of China and the Middle East. For North America, irrigation significantly increases precipitation under modern GHG forcing; this precipitation enhancement largely disappears under A1B forcing, reducing total latent heat fluxes and the overall irrigation cooling effect.
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Practical information
- General public
- Free
Contact
- Prof. Jed Kaplan