Table 1.
Best-fit stepwise multiple linear regression (MLR) models of monthly average daily solar radiation (MJ m-2 day-1) for seven geographical regions of Turkey.
| Region name | East Anatolia | Mediterranean | Aegean | Southeast Anatolia | Central Anatolia | Black Sea | Marmara | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Number of explanatory variables in MLR model | 5 | 6 | 7 | 4 | 5 | 6 | 5 | 6 | 7 | 1 | 2 | 3 | 3 | 4 | 5 | 1 | 2 | 2 | 3 | 4 |
| Intercept | -5.106 | -1.015 | 2.735 | -5.4 | 15 | 17.957 | -10.534 | -3.342 | -0.413 | 3.684 | -3.396 | -0.929 | -3.833 | -2.656 | -2.28 | 3.115 | 7.217 | 2.362 | 4.937 | 4.213 |
| Ho(S/So) (MJ m-2day-1) | 1.204 | 1.24 | 1.304 | 0.608 | 0.588 | 0.646 | 0.736 | 1.116 | 1.233 | 0.608 | 0.787 | 0.754 | 0.775 | 0.932 | 0.938 | 0.695 | 1.566 | 0.868 | 1.272 | 1.249 |
| PET (mm month-1) | -0.014 | -0.015 | -0.020 | 0.011 | 0.012 | 0.012 | -0.023 | -0.022 | -0.030 | -0.023 | -0.022 | |||||||||
| CLD (% month-1) | 0.181 | 0.197 | 0.205 | 0.132 | 0.064a | 0.021b | 0.107 | 0.127 | 0.113 | 0.074 | 0.084 | |||||||||
| ST (°C month-1) | -0.231 | -0.141 | -0.173 | 0.168 | 0.176 | 0.285 | -0.34 | -0.412 | -0.493 | |||||||||||
| S (h month-1) | -1.03 | -1.1 | -1.42 | -1.68 | -2.12 | -2.87 | -1.49 | -1.45 | ||||||||||||
| RHmax (% month-1) | 0.09 | 0.044 | 0.07 | -0.221 | -0.265 | |||||||||||||||
| Aspect (°) | 0.00328 | 0.0059 | 0.00665 | 0.00696 | 0.00375 | |||||||||||||||
| PPT (mm month-1) | -0.016 | -0.015 | -0.014 | |||||||||||||||||
| Elevation (m) | 0.00092 | 0.00113 | 0.00132 | |||||||||||||||||
| Tmax (°C month-1) | 0.418 | 0.49 | 0.514 | |||||||||||||||||
| RH (% month-1) | -0.08 | |||||||||||||||||||
| RHmin (% month-1) | -0.126 | |||||||||||||||||||
| DtS (km) | -0.0058 | |||||||||||||||||||
| RMSE | 1.16 | 1.11 | 1.07 | 1.42 | 1.33 | 1.27 | 1.37 | 1.33 | 1.3 | 1.35 | 0.969 | 0.896 | 1.86 | 1.75 | 1.71 | 1.45 | 1.1 | 1.61 | 1.53 | 1.46 |
| R2 (%) | 95.4 | 93.1 | ||||||||||||||||||
| R2adj (%) | 96.4 | 96.7 | 96.9 | 93.9 | 94.6 | 95.1 | 94.8 | 95.2 | 95.4 | 97.6 | 98.0 | 91.5 | 92.5 | 92.9 | 96.0 | 93.2 | 93.9 | 94.4 | ||
| Cp | 63.7 | 39.6 | 26.2 | 88 | 61.2 | 45.3 | 58.3 | 41.1 | 30.6 | 286.2 | 101.8 | 74 | 81.7 | 41.3 | 30 | 300.7 | 127.5 | 96 | 71.9 | 54.5 |
| V/P ratio (%) | 29 | 25 | 30 | 25 | 27 | 33 | 31 | |||||||||||||
| R2(%) for validation | 92.9 | 95.5 | 95.9 | 91.3 | 90.6 | 87.7 | 93.4 | 93.1 | 92.6 | 96.1 | 98.5 | 98.2 | 94.0 | 91.4 | 91.7 | 95.6 | 95.7 | 93.9 | 94.3 | 94.3 |
All the variables except for
P < 0.01 and
P > 0.05 are significant at P ≤ 0.001;
Ho: monthly average daily extraterrestrial solar radiation on a horizontal surface; S: day length; So: maximum possible sunshine duration; ST: soil temperature for a depth of 0 to 5 cm; RHmax: maximum relative humidity; PET: potential evapotranspiration; PPT: precipitation; RH: relative humidity; CLD: cloudiness; Tmax: maximum air temperature; RHmin: minimum relative humidity; DtS: distance to sea; RMSE: root mean square error; and V/P: ratio of number of stations of validation dataset to those of parameterization dataset.