SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...

Chapter 5 Modeling Grazing Effects on Coupled Water and Heat Fluxes in Inner Mongolia Grassland
Soil heat flux (MJ/m 2 /day)
7
6
5
4
3
2
1
0
-1
-2
UG 79 UG 99 WG HG
25-May 19-Jun 14-Jul 8-Aug 2-Sep 27-Sep
Time (days)
Fig. 5.8. Simulated soil surface heat fluxes for the four sites during the growing period
in 2006.
vegetation cover and near surface soil moisture. Under the same input of rainfall,
actual transpiration (Tp) decreases with increasing grazing intensity (Fig. 9),
which is characterized by only minor differences between the two ungrazed and
the moderately grazed sites, especially at the first stage of growing season, but
significantly lower value for the HG site during the whole growing period. With
increasing grazing intensity, ET slightly decreases because of increasing runoff
and drainage (Table 5). Especially in HG, the annual runoff reaches to about 6
mm in 2004 and 2006, respectively. Calculating mean Tp/ET ratios for the three
growing seasons, we find that about 48-52% of ET for UG 79, UG 99 and WG
are attributed to transpiration, and only 38% for HG. In comparison with the two
ungrazed sites, winter grazing does not show clear effects on the water
household components, while heavy grazing remarkably decrease water
interception by 50-55% and transpiration by 20-30%, and increase evaporation
by 25-40%.
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