Interannual Variations of Water and Carbon Dioxide Fluxes over a Semiarid Alpine Steppe on the Tibetan Plateau

Table 7

Multiple stepwise linear regression analysis showing the optimum model variables, their parameters, and relative importance on daily and monthly timescales for the water (ET, E, and T) and carbon (NEE, Re, and GPP) fluxes.

Flux (y)	Timescale		Optimum model	Relative importance of the parameters (scaled to 1)
ET (mm/d)	Day	0.71	y = −1.963 + 11.409 SWC + 0.004 Rn + 0.094 Ts − 0.542 VPD	SWC = 0.50; Rn = 0.29; Ts = 0.12; VPD = 0.10
	Month	0.91	y = −3.657 + 13.285 SWC + 0.095 Ts + 0.007 Rn	SWC = 0.64; Rn = 0.30; Ts = 0.06
E (mm/d)	Day	0.66	y = −1.471 + 8.549 SWC + 0.005 Rn − 0.84 VPD + 0.05 Ts	SWC = 0.47; Rn = 0.32; VPD = 0.17; Ts = 0.05
	Month	0.77	y = −0.32 + 11.978 SWC	SWC = 1.00
T (mm/d)	Day	0.51	y = −0.767 + 5.474 EVI + 0.407 VPD	EVI = 0.84; VPD = 0.16
	Month	0.70	y = −2.023 + 6.008 EVI + 0.183 WS + 0.049 Ts	EVI = 0.72; Ts = 0.15; WS = 0.13
NEE (gC m^−2s^−1)	Day	0.50	y = 0.922–8.980 EVI + 2.008 SWC + 0.002 Rn − 0.001 PAR	EVI = 0.85; SWC = 0.07; Rn = 0.05; PAR = 0.03
	Month	0.56	y = 1.076 – 6.927 EVI	EVI = 1
Re (gC m^−2s^−1)	Day	0.72	y = −1.018 + 2.381 EVI + 6.039 SWC + 0.064 Ts	SWC = 0.46; EVI = 0.38; Ts = 0.16
	Month	0.54	y = −0.339 + 6.767 EVI	EVI = 1
GPP (gC m^−2s^−1)	Day	0.76	y = −1.896 + 10.327 EVI + 0.053 Ts + 4.768 SWC − 0.003 Rn + 0.612 PAR	EVI = 0.65; SWC = 0.21; Ts = 0.08; Rn = 0.02; PAR = 0.04
	Month	0.79	y = −1.275 + 12.721 EVI	EVI = 1

Units: SWC (m³ m⁻³); Rn (W m⁻²); T_s (^oC); VPD (kPa); EVI (−); PAR ().