Reduction of tropical land region precipitation variability via transpiration.

Benjamin Lintner, J. David Neelin, Xianan Jiang, C. Boyce, Joshua Fisher, J. Perron, Terence Kubar, Jeonghoon Lee, John Worden Geophys. Res. Lett., submitted, Jan. 2012.
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Abstract It is well known that tropical rainforests exhibit low intraseasonal precipitation variability despite high annual-mean precipitation. Analyzing simulations of the NCAR atmospheric model coupled to the Community Land Model with an dwithout transpiration, it is shown that transpiration over tropical land regions effectively dampens temperature and precipitation variability over rainforests, thereby reducing the influence of large-scale disturbances. Since transpiration supplies more than 50% of the simulated total surface water flux over tropical rainforests, transpiration acts as a strong buffer on atmospheric moisture content. In the absence of transpiration, mean precipitation decreases while simulated precipitation variability rises substantially, with increasing incidence of both dry and wet extremes. The mechanisms that account for these changes in the mean precipitation and its distribution reflect a complex interplay of local, near-surface and remote moist dynamical processes. Coupled with anticipated hydrologic cycle impacts on global warming, it is argued that reduced transpiration associated with on-going large-scale land use change like deforestation is likely to increase the future occurrence of extreme precipitation and temperature events. Moreover, since plant productivity is higher under less variable hydroclimatic conditions, these results point to the intriguing possibility of a positive ecohydrological feedback between vegetation growth and reduced variability over rainforests.

Citation Lintner, B., J. D. Neelin, S. Jiang, C. Boyce, J. Fisher, J. Perron, T. Kubar, J.-E. Lee, J. Worden, 2012: Reduction of tropical land region precipitation variability via transpiration. Geophys. Res. Lett., submitted, Jan. 2012.

Acknowledgments. The authors thank I. Held and R. Pierrehumbert for their encouragement and A. Sobel, P. Gentine, and H. -S. Park for reviewing earlier versions of this manuscript. The work described here is performed at the Jet Propulsion Laboratory, California Institute of Technology under contracts from the National Aeronautics and Space Administration.