The paired t-test on temporal trends of heat degree days (HDD) driven by different influencing factors in each sub-region.

<p>Tr.ave, Tr<sub>mxt</sub>.ave and Tr<sub>phe</sub>.ave are the average value of regression coefficients at all stations of each sub-region. 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. SR, single-season rice region; DER, double-season early rice region.</p><p>*, significant at p < 0.05</p><p>**, significant at p < 0.01.</p><p>The paired t-test on temporal trends of heat degree days (HDD) driven by different influencing factors in each sub-region.</p>