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Katrina Hales, J. David Neelin and Ning Zeng

This study explores the sensitivity of tropical land climate to changes in Leaf Area Index (LAI) through surface conductance and albedo variations. Using different models and experiments, the research shows how low and moderate vegetation regions respond differently compared to rainforests. The study highlights the significant impact of surface properties on precipitation and evaporation, with surface conductance playing a larger role in more vegetated regions. The results provide insights into the mechanisms driving these climate sensitivities.

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Katrina Hales, J. David Neelin and Ning Zeng

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  1. Sensitivity of Tropical Land Climate to Leaf Area Index: Role of Surface Conductance versus Albedo • Katrina Hales, J. David Neelin and Ning Zeng

  2. Motivation • Other work: Sensitivity to individual land surface properties, complex land modeling, interactive vegetation. • Our approach: relative sensitivity to surface albedo (As) and surface conductance (gs).

  3. Model • Quasi-equilibrium Tropical Circulation Model (QTCM version 2.2)Neelin and Zeng 2000; Zeng, Neelin and Chou 2000 • Intermediate complexity model based on primitive equations,designed to capture tropical climate • Simple Land Model (SLand) • Zero net surface flux • Interactive soil moisture • Five land surface types based on observed vegetation class (De Fries and Townshend 1994) • Leaf Area Index (LAI; Los et al. 2000, Sellers et al. 1994)

  4. Surface Types rainforest other forest moderate vege. low vegetation desert/bare ground water

  5. As = a - b (1 - e-kLAI) Basis of surface albedo parameterization on LAI o observed ● reconstructed (annual average)

  6. Reconstructed Albedo from observed LAI (annual average)

  7. gs = gsmax β(w) (1 - e-kLAI)/k Basis of surface conductance parameterization on LAI o reconstructed (annual average)

  8. Experiment Regions

  9. -14 -13 -12 -11 -10 Low Vege. Rainforest Moderate Vege. -9 -8 -6 -4 -2 mm/mo Precip. change, LAI-33% Albedo-Only Cond.-Only

  10. Conclusions • In Tropics, low and moderate vegetation regions more sensitive to % change in LAI than rainforest regions. • Impacts on P and E by As (albedo) and gs (conductance) same sign, both significant, but dominance differs among vege. types. • gs larger influence in morevegetated regions • As larger influence in lessvegetated regions

  11. Mechanisms of P’ sensitivity differ • gs: local recycling of water; E’ drives P’ • E’≥P’ • As: column energy, thus moisture convergence • P’>E’ hales@atmos.ucla.edu

  12. Surface Types rainforest other forest moderate vege. low vegetation desert/bare ground water

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