Vegetation dynamics dominate the energy flux partitioning across typical ecosystem in the Heihe River Basin: Observation with numerical modeling

doi:10.1007/s11442-019-1677-z

Abstract

Abstract:

Understanding the controls on seasonal variation of energy partitioning and separation between canopy and soil surface are important for qualifying the vegetation feedback to climate system. Using observed day-to-day variations of energy balance components including net radiation, sensible heat flux, latent heat flux ground heat flux, and meteorological variables combined with an energy-balanced two-source model, energy partitioning were investigated at six sites in Heihe River Basin from 2014 to 2016. Bowen ratio (β) among the six sites exhibited significant seasonal variations while showed smaller inter-annual fluctuations. All ecosystems exhibit a “U-shaped” pattern, characterized by smaller value of β in growing season, with a minimum value in July, and fluctuating day to day. During the growing season, average Bowen ratio was the highest for the alpine swamp meadow (0.60 ± 0.30), followed by the desert riparian forest Populus euphratica (0.47 ± 0.72), the alpine desert(0.46 ± 0.10), the Tamarix ramosissima desert riparian shrub ecosystem (0.33 ± 0.57), alpine meadow ecosystem (0.32 ± 0.17), and cropland ecosystem (0.27 ± 0.46). The agreement of Bowen ratio between simulated and observed values demonstrated that the two-source model is a promising tool for energy partitioning and separation between canopy and soil surface. The importance of biophysical control explains the convergence of seasonal and annual patterns of Bowen ratio for all ecosystems, and the changes in Bowen ratio showed divergence among varied ecosystems because of different physiological responses to energy flow pathways between canopy and soil surface.

Key words: vegetation dynamics, seasonal variations, Bowen ratio, two-source modeling

WANG Pei, LI Xiaoyan, TONG Yaqin, HUANG Yongmei, YANG Xiaofan, WU Xiuchen. Vegetation dynamics dominate the energy flux partitioning across typical ecosystem in the Heihe River Basin: Observation with numerical modeling[J].Journal of Geographical Sciences, 2019, 29(9): 1565-1577.

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River section	Site	Longitude	Latitude	Altitude (m)	Dominant vegetation type	EC height (m)	Energy close
Upstream	Yakou	100.23°E	38.02°N	4101	Alpine meadow	3.5	0.53-0.55
	Dashalong	98.94°E	38.84°N	3739	Alpine swamp meadow	4.5	0.74-0.87
	A’rou	100.46°E	38.05°N	3044	Alpine meadow	3.5	0.95-0.96
Midstream	Daman	100.37°E	38.86°N	1556	Cropland	4.5	0.75-0.89
Downstream	Hunhelin	101.13°E	41.99°N	874	P.euphratica	22	0.87-0.91
Downstream	Sidaoqiao	101.14°E	42.00°N	873	T.ramosissima	8	0.85-0.89

Site	Item	N	Mean	S.D.	Minimum	Median	Maximum
Yakou	lET	24	31.01	19.67	6.04	28.02	68.97
	H	24	11.27	14.01	-7.55	13.53	37.43
A’rou	lET	36	41.13	32.84	2.74	30.36	103.23
A’rou	H	36	21.10	11.80	-7.51	20.71	42.08
Dashalong	lET	36	38.79	30.02	2.31	30.62	96.19
Dashalong	H	36	36.85	13.35	10.48	34.96	62.68
Daman	lET	36	58.49	45.86	4.59	51.95	152.86
Daman	H	36	20.91	15.82	-5.82	17.65	52.99
Hunheklin	lET	36	61.02	61.32	1.74	29.40	223.25
Hunheklin	H	36	30.82	29.39	-8.71	21.49	87.85
Sidaoqiao	lET	33	45.44	49.23	2.39	21.63	152.46
Sidaoqiao	H	36	39.22	26.77	-4.48	38.52	100.79

Site	Grow season	All year
A’rou	0.32 ± 0.17	0.96 ± 0.43
Dashalong	0.60± 0.30	2.17 ± 1.44
Yakou	0.46 ± 0.10	0.21 ± 0.18
Daman	0.27 ± 0.46	1.08 ± 0.50
Hunhelin	0.33 ± 0.57	2.56 ± 1.03
Sidaoqiao	0.47 ± 0.72	3.30 ± 0.12

Site	RMSD	I index	R²
A’rou	0.22	0.82	0.43
Dashalong	0.50	0.72	0.39
Yakou	0.44	0.64	0.31
Daman	0.48	0.71	0.28
Hunhelin	0.42	0.61	0.35
Sidaoqiao	0.28	0.85	0.47