Transcript Document

Growing temperate shrubs over arid to semi-arid regions in CLM-DGVM
Xiaodong ZENG and Xubin ZENG
Department of Atmospheric Sciences, The University of Arizona
4. Global Simulation
1. Introduction
 A large part of the land surface are arid to semiarid regions
(e.g.., from IPCC 1981-1990 climatology, about 27% of land
has annual precipitation less than 300 mm).
Figure 3. The global distribution of temperate shrubs at
the end of 100-year model simulation.
 Shrubs are the dominant vegetations over the arid to semiarid regions, but cannot compete with trees and grasses in the
humid region.
Fraction of coverage within 60N~60S :
 Observations show that shrubs are drought and hot tolerant.
They are generally shorter than trees, with small leaves and
small LAI, and slow growing rate.
Bare: 31%
Shrub: 11%
Tree: 36%
Grass: 22%
 Currently released version of NCAR CLM-DGVM
(Community Land Model 3 (CLM 3) coupled with the LPJ
dynamic global vegetation model) has not yet included shrubs.
Figure 1. Global land cover type map (calculated from MODIS product 12,
resolution 0.05x0.05) and contour of annual precipitation (calculated from IPCC
1981-1990 monthly mean climatology data, resolution 0.5x0.5. Red line shows the
contour for 300 mm of annual precipitation, and blue line for 800 mm) .
Figure 4. The map of dominant vegetation type at the
end of 100-year model simulation.
2. Model Revisions and Improvements
In order to realistically grow temperate shrub, we have made the following revisions and improvements of CLM-DGVM:
(1) a new function describing shrub’s ability of maintaining its photosynthesis under the stress of drought;
(2) a new phenology type describing the quickly response of shrub to rain event;
(3) a set of parameters for shrub morphology;
Figure 5. Difference in bare soil coverage at the
end of 100-year model simulation.
(4) a new scheme for the light competition among trees-grasses-shrubs.
Exp: revised CLM-DGVM with shrub presented.
Ctrl: standard CLM-DGVM.
3. Single Point Simulations
Global bare soil coverage decreases from 46%
(Ctrl) to 37% (Exp).
(A)
(B)
EXP
(C)
CTRL
(D)
Figure 2. The history of vegetation coverage at four locations showing the competition and
coexistence of shrubs, grasses, and trees. The annual precipitations are: (A) 194 mm; (B) 364
mm; (C) 564 mm; and (D) 757 mm, respectively.
Figure 6. The fraction of vegetation coverage (between 60N~60S) vs. annual precipitation.
P (mm yr-1)
PFT
194
shrub
364
C3
shrub
564
C3
shrub
C3
757
tree
C3
tree
FC (%)
83.3
0.6
48.3
51.5
9.0
70.2
20.8
12.0
88.0
LAI
0.25
2.01
0.92
2.81
1.02
2.49
3.33
2.13
6.38
Reference:
Levis, S., G.B., Bonan, M. Vertenstein, and K.W. Oleson, 2004: The Community Land Model’s dynamic global vegetation
model (CLM-DGVM): technical description and user’s guide. NCAR Tech. Note TN-459+IA, 50pp.
Contact Information:
Htop (m)
1.29
0.5
1.28
0.7
0.99
0.66
3.99
Table abbreviations:
C3: C3 non-arctic grass; tree: broadleaf deciduous temperate tree.
P: precipitation; PFT: plant functional type.
FC: fraction of coverage; LAI: leaf area index; Htop: height of top of canopy.
0.53
11.6
Xiaodong Zeng, Department of Atmospheric Sciences, The University of Arizona, 1118E 4th St, Tucson, AZ 85721. Email:
[email protected].