SIMULATING SEASONAL AND INTERANNUAL VARIATIONS OF ECOSYS- TEM EVAPOTRANSPIRATION AND ITS COMPONENTS IN INNER MONG- OLIA STEPPE WITH VIP MODEL

doi:10.3773/j.issn.1005-264x.2008.05.010

Abstract

Abstract:

Aims Evapotranspiration (ET) plays an important role in arid and semiarid temperate grassland where water availability is a major limiting factor for ecosystem functions. Understanding temporal variation of ET can help explain the surface-atmosphere interaction and its ecological function in grassland ecosystems. Partitioning total ET into its components of evaporation from soil (E) and transpiration from plants (T) is important for understanding the biotic and abiotic factors that control water balance. Our objectives were to simulate the seasonal and interannual variations of ET and its components, analyze the contribution of the components to ETand analyze influencing factors.

Methods We used flux data derived from eddy covariance technology over Inner Mongolia steppe (43°32′ N, 116°40′ E), measuredLAIand MODIS data from 2003 to 2005 and parameterized VIP (Vegetation interface processes) model to simulate ET of the grassland. The results were validated using half-hourly latent heat fluxes (LE) and net radiation (R_n) estimated from eddy covariance measurements.

Important findings VIP model can effectively simulate latent heat fluxes of the grassland (R²=0.80). In 2003 and 2004, precipitation (P) was near average and annual ET was 337 and 338 mm, respectively, which were greater than P. In the drier year of 2005, annual ET was 223 mm, which was higher than P. On average, E andT made relatively equivalent contributions to ET. About 83% of annual EToccurred during the growing season. Ewas the primary component of ET before June and was exceeded by Tafter that. The monthly totals of both ET and Treached maxima in July and August. Total ETduring July and August accounted for 43% of the annual amount. ETwas strongly correlated with LAI and moderately correlated with P. E changed little during the growing season, and the difference in ET was accounted for T.

Key words: Leymus chinensis steppe, VIP model, evapotranspiration, precipitation, canopy conductance

WANG Yong-Fen, MO Xing-Guo, HAO Yan-Bin, GUO Rui-Ping, HUANG Xiang-Zhong, WANG Yan-Fen. SIMULATING SEASONAL AND INTERANNUAL VARIATIONS OF ECOSYS- TEM EVAPOTRANSPIRATION AND ITS COMPONENTS IN INNER MONG- OLIA STEPPE WITH VIP MODEL[J]. Chin J Plant Ecol, 2008, 32(5): 1052-1060.

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URL: https://www.plant-ecology.com/EN/10.3773/j.issn.1005-264x.2008.05.010

https://www.plant-ecology.com/EN/Y2008/V32/I5/1052

Figures/Tables 7

Fig.1 The simulated and measured latent heat flux (LE) and net radiation (Rn) from 2003 to 2005

Fig.2 The simulated (line) and measured (dot) daily evapotranspiration (ET ) from 2003 to 2005

Fig. 3 The annual total precipitation (P), evapotranspiration (ET), transpiration from plant (T) and evaporation from soil (E) from 2003 to 2005

Fig. 4 The monthly P-ET and T/ETfrom 2003 to 2005

Fig. 5 Seasonal variations of daily total T, E and LAIin the growing season from 2003 to 2005

Table 1 The correlation coefficients of ET, E, T and Rn, LAI, VPD, P and the multiple liner regression equations

变量 Variable	叶面积指数 LAI	饱和水汽压差 VPD	降水 P	净辐射 R_n	方程 Equation
蒸散 ET	0.970	0.800	0.916	0.826	ET= -0.930 + 1.091 LAI+ 0.042 VPD+0.046 P+ 0.002 R_n (r = 0.994)
蒸发E	0.775	0.900	0.753	0.883	E = 0.692 + 0.034 LAI + 0.037 VPD + 0.050 P+ 0.002 R_n (r = 0.942)
蒸腾T	0.992	0.696	0.924	0.740	T = -1.614 + 1.047 LAI + 0.005 VPD - 0.008 P+ 0.001 R_n (r = 0.993)

Fig.6 Seasonal variation of daily canopy conductance from 2003 to 2005

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