The response of the South Asian Summer Monsoon circulation to intensified irrigation in global climate model simulations

Sonali Mcdermid, Michael J. Puma, Benjamin I. Cook

    Research output: Contribution to journalArticle

    Abstract

    Agricultural 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.

    Original languageEnglish (US)
    Pages (from-to)21-36
    Number of pages16
    JournalClimate Dynamics
    Volume42
    Issue number1-2
    DOIs
    StatePublished - Jan 2014

    Fingerprint

    global climate
    climate modeling
    monsoon
    irrigation
    summer
    simulation
    twentieth century
    greenhouse gas
    surface energy
    energy balance
    agricultural intensification
    temperature
    temperature gradient
    general circulation model
    land surface
    warming
    moisture
    rainfall

    Keywords

    • Irrigation
    • Latent heating
    • Monsoon intensity
    • South Asian Summer Monsoon

    ASJC Scopus subject areas

    • Atmospheric Science

    Cite this

    The response of the South Asian Summer Monsoon circulation to intensified irrigation in global climate model simulations. / Mcdermid, Sonali; Puma, Michael J.; Cook, Benjamin I.

    In: Climate Dynamics, Vol. 42, No. 1-2, 01.2014, p. 21-36.

    Research output: Contribution to journalArticle

    Mcdermid, Sonali ; Puma, Michael J. ; Cook, Benjamin I. / The response of the South Asian Summer Monsoon circulation to intensified irrigation in global climate model simulations. In: Climate Dynamics. 2014 ; Vol. 42, No. 1-2. pp. 21-36.
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    AB - Agricultural 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.

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    KW - Latent heating

    KW - Monsoon intensity

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