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The Response of the South Asian Summer Monsoon Circulation to Intensified Irrigation in Global Climate Model SimulationsAgricultural intensification in South Asia has resulted in the expansion and intensification of surface irrigation over the twentieth century. The resulting changes to the surface energy balance could affect the temperature contrasts between the South Asian land surface and the equatorial Indian Ocean, potentially altering the South Asian Summer Monsoon (SASM) circulation. Prior studies have noted apparent declines in the monsoon intensity over the twentieth century and have focused on how altered surface energy balances impact the SASM rainfall distribution. Here, we use the coupled Goddard Institute for Space Studies ModelE-R general circulation model to investigate the impact of intensifying irrigation on the large-scale SASM circulation over the twentieth century, including how the effect of irrigation compares to the impact of increasing greenhouse gas (GHG) forcing. We force our simulations with time-varying, historical estimates of irrigation, both alone and with twentieth century GHGs and other forcings. In the irrigation only experiment, irrigation rates correlate strongly with lower and upper level temperature contrasts between the Indian sub-continent and the Indian Ocean (Pearson's r = -0.66 and r = -0.46, respectively), important quantities that control the strength of the SASM circulation. When GHG forcing is included, these correlations strengthen: r = -0.72 and r = -0.47 for lower and upper level temperature contrasts, respectively. Under irrigated conditions, the mean SASM intensity in the model decreases only slightly and insignificantly. However, in the simulation with irrigation and GHG forcing, inter-annual variability of the SASM circulation decreases by *40 %, consistent with trends in the reanalysis products. This suggests that the inclusion of irrigation may be necessary to accurately simulate the historical trends and variability of the SASM system over the last 50 years. These findings suggest that intensifying irrigation, in concert with increased GHG forcing, is capable of reducing the variability of the simulated SASM circulation and altering the regional moisture transport by limiting the surface warming and reducing land-sea temperature gradients.
Document ID
20150002152
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1007/s00382-013-1786-9
Authors
Shukla, Sonali P. (Oak Ridge Associated Universities Greenbelt, MD, United States)
Puma, Michael J. (Columbia Univ. New York, NY, United States)
Cook, Benjamin I. (NASA Goddard Inst. for Space Studies New York, NY, United States)
Date Acquired
February 25, 2015
Publication Date
May 5, 2013
Publication Information
Publication: Climate Dynamics
Publisher: Springer
Volume: 42
Issue: 2-Jan
Subject Category
Meteorology And Climatology
Report/Patent Number
GSFC-E-DAA-TN18828
Funding Number(s)
CONTRACT_GRANT: NNX08AJ75A
CONTRACT_GRANT: NNX14AB99A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
amplification
trends
Asia
histories
surface energy
irrigation
Indian Ocean
monsoons
variability

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