Fourth Study Conference on BALTEX Scala Cinema Gudhjem

Maximum 5 day precipitation (mm)
Number of dry spells
16
14
12
10
8
6
4
2
a
The multiple-regression method SDSM identified an area
south-west of the study area as the most influential.
Downscaling was also improved when seasonality was
explicitly included. Seasonality was introduced in different
ways; with a sliding time window of varying size or by
splitting the data into quarter years or half years. The
circulation patterns producing precipitation in Sweden are
clearly different between summer and winter half years
(Figure 3).
References
Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven,
D., Gandin, L., Iredell, M., Saha, S., White, G.,
Woollen, J., Zhu, Y., Chelliah, M., Ebisuzaki, W.,
Higgins, W., Janowiak, J., Mo, K.C., Ropelewski, C.,
Wang, J., Leetmaa, A., Reynolds, R., Jenne, R., Joseph,
D., 1996. NCEP/NCAR 40-year reanalysis project.
Bulletin of the American Meteorological Society 77,
437-471, 1996.
120
100
80
60
40
20
- 121 -
Obs
PCA
TWS
Baseline
0
8 10 12 14 16 18 20 22 24 26
Figure 2. Distribution of dry spells (longer than 7 Dry−spell days) for observed length (days) and downscaled precipitation data from 1991-
1997. The downscaling is based on the analogue method with the PCA and TWS techniques and compared to a random
baseline.
Stehlik, J., Bardossy, A., Multivariate stochastic
downscaling model for generating daily precipitation
series based on atmospheric circulation, Journal of
Hydrology 256, 120-141, 2002.
Wilby, R. L., Dawson, C. W., Barrow, E. M., SDSM - a
decision support tool for the assessment of regional
climate change impacts, Environmental Modelling &
Software 17, 147-159, 2002.
Zorita, E., von Storch, H., The analogue method as a
simple statistical downscaling technique: Comparison
with more complicated methods, Journal of Climate
12, 2474-2489, 1999.
0
OBS MOFRBC SDSM PCA TWS
Figure 3. Maximum 5-day precipitation for the period 1991-1997 given as an example of the relative merits of the different downscaling
methods. Observed data are shown together with downscaled using the MOFRBC, SDSM and analogue methods, the latter using the PCA
and TWS techniques. Grey bars denote the summer half of the year and black bars the winter half of the year.