Table 2. The paired t-test on temporal trends of heat degree days (HDD) driven by different influencing factors in each sub-region.
| Regions | Average trends of HDD driven by phenology shift and by variations of maximum temperature Tr.ave (°C·d·y-1) | Average trends of HDD driven by variations of maximum temperature Trmxt.ave (°C·d·y-1) | Average trends of HDD driven by phenology shift Trphe.ave (°C·d·y-1) | P-value |
|---|---|---|---|---|
| S-NMLYtz | 0.031 | 0.042 | -0.011 | 0.000** |
| S-SWP | 0.245 | 0.110 | 0.135 | 0.842 |
| DE-SMLYtz | 0.323 | 0.590 | -0.267 | 0.046* |
| DE-SC | 0.178 | 0.249 | -0.071 | 0.000** |
| SR | 0.006 | 0.102 | -0.096 | 0.379 |
| DER | 0.276 | 0.455 | -0.179 | 0.010** |
| South China | 0.175 | 0.311 | -0.136 | 0.018* |
Tr.ave, Trmxt.ave and Trphe.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.
*, significant at p < 0.05
**, significant at p < 0.01.