Table 4. Regression coefficients and determination coefficients (R²) of statistical model for grain yield in response to temperature variables (per unit).

Sub-regions	Considering HDD and GDD (typeⅠ)				Considering only HDD (typeⅡ)
	β0	β1	β2	R2	β0	β2	R2
S-NMLYtz	0.011	0.0005	-0.011**	0.138	0.013	-0.012**	0.134
S-SWP	0.024	0.0009*	-0.008**	0.173	0.021	-0.007**	0.112
DE-SMLYtz	0.005	-0.0007	-0.009**	0.215	0.004	-0.009**	0.208
DE-SC	0.007	-0.0006	-0.010**	0.295	0.006	-0.011**	0.290

β₁ and β₂ are the coefficients for ΔGDD and ΔHDD in Eq (4), respectively, which represent the sensitivities of grain yield to temperature variables. Significance of β₁, β₂ was tested at p<0.05 (*) and p<0.01 (**). Numbers with black bold indicate the regression coefficients for the selected type of statistical model. S-NMLYtz, single-season rice sub-region in the northern Middle and Lower Reaches of Yangtze River; S-SWP, single-season rice sub-region in Southwest Plateau; DE-SMLYtz, double-season early rice sub-region in the southern Middle and Lower Reaches of Yangtze River; DE-SC, double-season early rice sub-region in Southern China.