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Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss
Quantifying uncertainty in monthly and seasonal forecasts of indices
Christoph Spirig, Irina Mahlstein, Jonas Bhend, and Mark Liniger
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2 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Current monthly and seasonal forecasts • tercile probabilities
3-monthly (weekly)
averages of temperature
for seasonal (monthly) forecasts
bar plots, maps, climagrams
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3 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Customers of ER and SFC
• commercial customers • (re)insurance • energy providers • global perspective
• general public
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4 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Improve usability of seasonal forecasts
• forecasts of indices in addition to basic met. variables • indices: (non-linear) aggregation of meteorological
parameter over given period • indices often include thresholds • direct relevance for users
• forecasts with a user perspective while avoiding complex
impact models
www.euporias.eu
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5 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Vision
• combining monitoring and forecasts (IFS-ENS, IFS-ENS-EXT, …, seamless)
• input: long-term forecasts @daily resolution, calibrated
Soil moisture index
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6 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Vision
• appropriate representation of uncertainties
• skill of index forecasts ?
Soil moisture index
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7 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Analysis scheme
Daily time series from seasonal forecasts + hindcasts
Observations/ ERA-Interim
Calibration
Calibrated daily series
Verification
Indicators from observations
Forecasts of indicators
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8 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Challenge: bias correction of daily data
Problem: 30 years of observations not enough to calculate daily climatology • approach: apply low-pass filter • evaluated using perfect model approach
(Mahlstein et al., JGR 2015)
30 yrs average hindcast mean fit to 30yrs mean
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9 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Bias correction of daily data
• CRPS of average temperature forecast in JJA (May init)
raw corrected
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10 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Skill of CDD forecast
• CRPSS of average temperature forecast in JJA (May init)
raw calibrated
worse better
than climatology
worse better
than climatology
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11 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Example of index forecasts
• temperature based indices Heating Degree Days (HDD) and Cooling Degree Days (CDD)
• sums of daily temperatures Ti below / above given threshold (TH)
• proxies for heating/cooling energy demand
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12 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Skill in forecasts of indicators vs skill of the underlying variable
Summer Winter
tem
pera
ture
H
DD
/CD
D
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13 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Skill in forecasts of indicators vs skill of the underlying variable
Summer Winter
tem
pera
ture
H
DD
/CD
D
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14 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Skill of absolute vs tercile forecasts
CDD forecast JJA, May initialization
CRPSS (absolute) RPSS (terciles)
worse better
than climatology
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15 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Verification against observation data sets E
RA
-Inte
rim
Summer Winter
E-O
BS
E-OBS data set: www.ecad.eu
HDD/CDD forecasts for months 2-4, Nov/May init
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16 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Lessons learnt
• Daily calibration improves skill in forecasts of climate indices
• Skill largely insensitive to choice of calibration method
• Skill in index at most as large as skill in underlying variable • Skill in seasonal index predictions is limited
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17 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Implications for use of forecasts
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18 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Forecast presentation
Basis: HDD forecast as tercile summary
lower tercile prob.
middle tercile prob.
upper tercile prob.
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19 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Forecast presentation
Basis: HDD forecast as tercile summary
lower tercile prob.
middle tercile prob.
upper tercile prob.
combine with skill information!
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20 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
User perspective for aggregation of forecast information
• example of CDD forecast
• energy perspective: • cooling energy demand
• health perspective
• how many people are affected?
→ use population density for weighting of CDD forecast/obs
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21 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Skill of CDD forecast (RPSS)
CDD prediction for August (May initialization)
same analysis for CDD weighted by population density, aggregated to country level
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22 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Conclusions
• potential to provide added value in certain areas
• be careful in not provoking overinterpretation • combine skill and forecast information
• promote the use of «climatological forecast»
• added value by considering natural variability
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23 UEF 2015 | Monthly and seasonal forecasts of indices C. Spirig, I. Mahlstein, J. Bhend, M. Liniger
Thank you !