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Mid-Holocene Vegetation Feedbacks and

Abrupt Change over North Africa

Collaborators: Zhengyu Liu, Robert Gallimore, Yi Wang, Sam Levis, John Kutzbach, J.P. Argenti, I.C. Prentice

Funding: DOE

Publications:
Notaro, M., Y. Wang, Z. Liu, R. Gallimore, and S. Levis, 2008: Combined statistical and dynamical assessment of
    simulated vegetation-rainfall interactions in North Africa during the mid-Holocene. Global Change Biology, 14,
    347-368.
Wang, Y., M. Notaro, Z. Liu, R. Gallimore, S. Levis, and J. E. Kutzbach, 2007: Detecting vegetation-precipitation
    feedbacks in mid-Holocene North Africa from two climate models. Climate of the Past, 3, 961-975.
Liu, Z., M. Notaro, J. P. Argenti, and R. G. Gallimore, 2010: Indirect vegetation-soil moisture feedback with
    application to Holocene North Africa climate. Global Change Biology, 16, 1733-1743.
Liu, Z., Y. Wang, R. Gallimore, F. Gasse, T. Johnson, P. deMenocal, J. Adkins, M. Notaro, I. C. Prentice, J.
    Kutzbach, R. Jacob, P. Behling, L. Wang, and E. Ong, 2007: Simulating the transient evolution and abrupt change
    of North Africa atmosphere-ocean-terrestrial ecosystem in the Holocene. J. Quaternary Science, 26, 1818-1837.
Liu, Z., Y. Wang, R. Gallimore, M. Notaro, and I. C. Prentice, 2006: On the cause of abrupt vegetation collapse in
    North Africa during the Holocene: Climate variability vs. vegetation feedback. Geophysical Research Letters, 33,
    L22709, doi:10.1029/2006GL028062.

Methods: The abrupt collapse of vegetation across North Africa around 5.5K and vegetation feedbacks on precipitation over that region in the mid-Holocene are investigated using the FOAM-LPJ fully coupled global climate model.

Key finding: FOAM-LPJ successfully simulated the abrupt collapse in North African vegetation cover in response to a gradual reduction in rainfall (due to orbital forcing). Vegetation feedbacks, as revealed both statistically using lagged covariances and dynamically using ensemble experiments, are negative on precipitation over North Africa in FOAM-LPJ during the mid-Holocene.

During the mid-Holocene, vegetation was quite abundant across the southern Sahara. This is simulated by FOAM-LPJ fully coupled global climate model for the mid-Holocene, around 6K years ago. Ensemble experiments in which vegetation cover fraction is reduced by 0.2 over the southern Sahara display an increase in precipitation. This suggests a negative feedback of vegetation on precipitation during that period.