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. Other work: Sensitivity to individual land surface properties, complex land modeling, interactive vegetation. Our approach: relative sensitivity to surface albedo (A s ) and surface conductance (g s ). Motivation

3. 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) Model

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

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

6. Reconstructed Albedo from observed LAI (annual average)

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

9. Experiment Regions

10. North Africa Experiment LAI - 33% P’ E’ Rainforest ΔLAI=-1.5 LAI A s -only g s -only -12.5 -3.2 -9.6 -12.5 -0.4 -12.1 Moderate Vege. ΔLAI=-0.7 LAI A s -only g s -only -14.2 -7.5 -6.9 -11.2 -1.7 -9.6 Low Vege. ΔLAI=-0.4 LAI A s -only g s -only -16.2 -10.5 -6.8 -9.7 -1.8 -8.3

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

12. North Africa Experiment LAI - 33% P’ E’ Rainforest ΔLAI=-1.5 LAI A s -only g s -only -12.5 -3.2 -9.6 -12.5 -0.4 -12.1 Moderate Vege. ΔLAI=-0.7 LAI A s -only g s -only -14.2 -7.5 -6.9 -11.2 -1.7 -9.6 Low Vege. ΔLAI=-0.4 LAI A s -only g s -only -16.2 -10.5 -6.8 -9.7 -1.8 -8.3

13. North Africa Experiment LAI - 33% P’ E’ Rainforest ΔLAI=-1.5 LAI A s -only g s -only -12.5 -3.2 -9.6 -12.5 -0.4 -12.1 Moderate Vege. ΔLAI=-0.7 LAI A s -only g s -only -14.2 -7.5 -6.9 -11.2 -1.7 -9.6 Low Vege. ΔLAI=-0.4 LAI A s -only g s -only -16.2 -10.5 -6.8 -9.7 -1.8 -8.3

14. Conclusions In Tropics, low and moderate vegetation regions more sensitive to % change in LAI than rainforest regions. Impacts on P and E by A s (albedo) and g s (conductance) same sign, both significant, but dominance differs among vege. types. g s larger influence in more vegetated regions A s larger influence in less vegetated regions

15. Mechanisms of P’ sensitivity differ g s : local recycling of water; E’ drives P’ E’≥P’ A s : column energy, thus moisture convergence P’>E’ hales@atmos.ucla.edu

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