Table 2 Liner trends of percentage of area with regional average weekly VHI at different ranges for the period of 1982–2016 in Jing-Jin-Jin region, Beijing and Tianjin cities.
Region | VHI range | Linear equation | Trend | Average value (%) | Max value (%) |
|---|---|---|---|---|---|
Jing-Jin-Ji region | VHI < 5 | y = −0.0239x + 48.4540 | Decrease | 0.65 | 12.75 |
VHI < 15 | y = − 0.0859x + 174.7868 | Decrease | 3.07 | 31.26 | |
VHI < 25 | y = − 0.2123x + 433.9317 | Decrease | 9.48 | 57.49 | |
VHI < 35 | y = − 0.3935x + 808.8915 | Decrease | 22.03 | 83.20 | |
VHI < 40 | y = − 0.4735x + 977.5322 | Decrease | 30.64 | 90.49 | |
40 < VHI < 60 | y = 0.1543x − 259.3224 | Increase | 49.19 | 87.76 | |
VHI > 60 | y = 0.3195x − 618.6419 | Increase | 20.17 | 81.38 | |
Beijing City | VHI < 5 | y = − 0.0055x + 11.6835 | Decrease | 0.72 | 22.80 |
VHI < 15 | y = − 0.0038x + 11.3928 | Decrease | 3.84 | 47.54 | |
VHI < 25 | y = − 0.0215x + 54.5699 | Decrease | 11.55 | 72.05 | |
VHI < 35 | y = − 0.1146x + 254.4341 | Decrease | 25.20 | 91.46 | |
VHI < 40 | y = − 0.1793x + 392.5272 | Decrease | 34.04 | 96.02 | |
40 < VHI < 60 | y = − 0.0163x + 79.5513 | Decrease | 46.95 | 94.85 | |
VHI > 60 | y = 0.1956x − 372.1544 | Increase | 19.01 | 85.31 | |
Tianjin City | VHI < 5 | y = 0.0104x − 19.8853 | Increase | 0.80 | 28.83 |
VHI < 15 | y = 0.0324x − 60.8101 | Increase | 4.22 | 76.91 | |
VHI < 25 | y = 0.0386x − 65.1976 | Increase | 12.95 | 94.13 | |
VHI < 35 | y = − 0.0256x + 76.8262 | Decrease | 28.72 | 97.83 | |
VHI < 40 | y = − 0.0535x + 145.6432 | Decrease | 38.63 | 98.85 | |
40 < VHI < 60 | y = 0.0553x − 64.5055 | Increase | 46.07 | 82.28 | |
VHI > 60 | y = − 0.0019x + 19.1741 | Decrease | 15.31 | 80.10 |
