Table 3. Approximate significance of smooth terms in Shaanbei upland plateau and Guanzhong basin in Shaanxi Province, China, 2005–2018.
| Variables | Regions | Effective degrees of freedom | F | p |
|---|---|---|---|---|
| s(Air temperature) | Guanzhong basin | 6.41 | 1.80 | 0.08 |
| Shaanbei upland plateau | 1.00 | 0.86 | 0.35 | |
| s(Lag in air temperature) | Guanzhong basin | 7.73 | 1.49 | 0.15 |
| Shaanbei upland plateau | 1.59 | 4.34 | 0.01 | |
| s(Relative humidity) | Guanzhong basin | 5.44 | 3.61 | <0.001 |
| Shaanbei upland plateau | 1.00 | 0.12 | 0.73 | |
| s(Lag in relative humidity) | Guanzhong basin | 6.62 | 4.06 | <0.001 |
| Shaanbei upland plateau | 1.00 | 4.21 | 0.04 | |
| s(Sunshine duration) | Guanzhong basin | 2.37 | 2.71 | 0.04 |
| Shaanbei upland plateau | 1.75 | 3.18 | 0.04 | |
| s(Lag in sunshine duration) | Guanzhong basin | 9.41 | 1.66 | 0.09 |
| Shaanbei upland plateau | 1.00 | 4.64 | 0.03 | |
| s(Evaporation) | Guanzhong basin | 3.47 | 4.60 | <0.001 |
| Shaanbei upland plateau | 2.31 | 1.63 | 0.21 | |
| s(Lag in evaporation) | Guanzhong basin | 1.30 | 6.37 | 0.01 |
| Shaanbei upland plateau | 1.00 | 4.01 | 0.05 | |
| s(Rainfall) | Guanzhong basin | 8.61 | 2.38 | 0.01 |
| Shaanbei upland plateau | 1.00 | 0.12 | 0.73 | |
| s(Lag in rainfall) | Guanzhong basin | 8.23 | 1.75 | 0.08 |
| Shaanbei upland plateau | 1.00 | 0.42 | 0.52 |
Notes.
*
Summary of the GAMM smooth terms, their p-values and effective degrees of freedom are listed. We constructed the final model based on current monthly meteorological factors, temperature lag of 4 months, rainfall lag of 3 months, relative humidity lag of 2 months, sunshine duration lag of 6 months and evaporation lag of 5 months in Shaanbei upland plateau. Meanwhile, we constructed the final model for the Guanzhong basin based on current monthly meteorological factors and previous meteorological factors with lag times 1 month greater than those in Shaanbei upland plateau.