Fig. 1
The location of the thermometer readings and the rain gauge records (µ) over Europe (a) and the temperature stations from China (b). The colour coding is according to the mean values recorded.
Fig. 2
Comparison between observed seasonal mean temperature anomaly and corresponding downscaled results using the PCA-based strategy and a traditional approach.
Table 1. Correlation score for downscaled seasonal mean temperature anomalies from the cross-validation
DJF
PCA0.94 (0.93, 0.94)0.89 (0.89, 0.90)0.93 (0.92, 0.93)0.90 (0.90, 0.91)0.93 (0.92, 0.93)0.82 (0.81, 0.83) trad.0.92 (0.92, 0.93)0.89 (0.88, 0.89)0.92 (0.91, 0.92)0.89 (0.88, 0.89)0.91 (0.91, 0.92)0.77 (0.76, 0.78)JJA
PCA0.82 (0.80, 0.83)0.77 (0.76, 0.79)0.80 (0.79, 0.82)0.78 (0.77, 0.80)0.80 (0.79, 0.81)0.74 (0.73, 0.76) trad.0.80 (0.79, 0.81)0.75 (0.74, 0.77)0.80 (0.79, 0.81)0.76 (0.74, 0.77)0.79 (0.77, 0.80)0.69 (0.67, 0.71)Domain
W (°E)−15.00−50.00−10.00−70.00−25.00−90.00 E (°E)25.0040.0020.0030.0035.0050.00 S (°N)45.0035.0050.0040.0040.0030.00 N (°N)65.0075.0060.0067.0070.0075.00 N PCA 202020202020
[i] The highest score for each trial is shown in bold and the numbers in the bracket indicate the 95% confidence interval for the correlation estimate. The standard deviation of the PCA-based scores was 0.07, whereas the standard deviation for the traditional method was 0.08, suggesting that the PCA-based ESD was less sensitive to the choice of predictor size.
Fig. 3
Comparison between observed seasonal mean temperature anomaly and corresponding downscaled results using the PCA-based strategy and a traditional approach.
Fig. 4
Comparison between downscaled results and observations for a single station where (a) only 4 PCAs were retained and with the lowest correlation, (b) only 4 PCAs were retained and with the highest correlation, (c) only 10 PCAs were retained and with the lowest correlation, and (d) only 20 PCAs were retained and with the lowest correlation. The observed data are shown in black, the PCA-based downscaled results in red, and the traditional downscaled results in blue.
Fig. 5
The covariance of the seasonal mean anomalies of the station data x o (left) and the difference between the two downscaling strategies in terms of (middle and right).
Fig. 6
Comparison between observed seasonal mean temperature anomaly and corresponding downscaled results using the PCA-based strategy and a traditional approach after having excluded the four leading PCA modes. Left panel shows results for the winter and right for the summer.
Fig. 7
Comparison between station-wise RMSE for a number of downscaling exercises with different domain sizes. The PCA-based results are plotted along the x-axis and results from the traditional approach along the y-axis. The units are degree C (anomalies). Points above the diagonal indicate higher skill for the PCA-based downscaling strategy. The different colours represent different predictor domain. Left panel shows results for the winter and right for the summer.
{ label needed for table-wrap[@id='T0002'] }
Table 2. Skill scores for the PCA-based and traditional ESD for China
DJF
PCA0.870.860.870.870.860.86 trad.0.830.820.820.840.830.82JJA
PCA0.710.690.720.730.700.70 trad.0.700.710.700.680.650.64 N PCA 202020202020Domain
W (°E)70.0065.0060.0070.0065.0060.00 E (°E)140.00145.00150.00140.00145.00150.00 S (°N)15.0015.0015.0010.0010.0010.00 N (°N)55.0055.0055.0060.0060.0060.00 N PCA 202020202020
{ label needed for table-wrap[@id='T0003'] }
Table 3. The results of the PCA-based ESD test for Northern China
DJF
PCA0.890.890.890.880.880.90 trad.0.880.890.860.860.820.89JJA
PCA0.810.820.790.740.750.79 trad.0.740.800.720.680.690.78Domain
W (°E)100.00105.0095.0090.0080.00100.00 E (°E)130.00125.00135.00140.00140.00130.00 S (°N)25.0030.0020.0015.0015.0030.00 N (°N)55.0050.0060.0065.0055.0050.00 N PCA 202020202020
Table 4. The results for PCA-based and traditional ESD for the annual wet-day mean precipitation taken from 62 Norwegian rain gauge records over the period 1907–1997
PCA0.23 (0.2, 0.26)0.23 (0.2, 0.27)0.24 (0.21, 0.27)0.26 (0.22, 0.29)0.2 (0.17, 0.24)0.31 (0.28, 0.34)0.18 (0.14, 0.21)0.33 (0.29, 0.36)trad.0.26 (0.23, 0.3)0.26 (0.23, 0.3)0.26 (0.23, 0.3)0.15 (0.12, 0.18)0.24 (0.2, 0.27)0.27 (0.23, 0.3)0.19 (0.16, 0.22)0.26 (0.22, 0.29)Domain
W (°E)−15−15−15−50−10−70−25−90 E (°E)2525254020303550 S (°N)4545453550−70−25−90 N (°N)6565657560303550 N PCA 204102020202020
[i] The entries are correlation scores from the cross-validation. Note that the only difference for the three first entries was retaining different numbers of PCAs for the stations (same predictor region). The predictor was the saturation water pressure estimated from the NCEP/NCAR reanalysis 2-metre temperature based on the Clausius–Clapeyron equation. The highest value for each test is shown in bold.