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Katrina Hales, J. David Neelin and Ning Zeng

Sensitivity of Tropical Land Climate to Leaf Area Index: Role of Surface Conductance versus Albedo. Katrina Hales, J. David Neelin and Ning Zeng. Motivation. Other work: Sensitivity to individual land surface properties, complex land modeling, interactive vegetation.

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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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