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December 2015in Europe
Geert Jan van Oldenborgh, KNMIin collaboration with the Oxford crew
Temperature anomalies
Temperature anomalies
Temperature anomalies
Temperature anomalies
Temperature anomalies
Z500 anomalies
Rank of December 2015 T2m
Rank of December 2015 T2m
Return times in the Netherlands
December temperatures showed no trend before 2015
Return times in the Netherlands
Return times in the Netherlands
Return time of Dec2015 T2m in 1900
Assuming a GPD shifting with Tglobal
Return time of Dec2015 T2m in 2015
Assuming a GPD shifting with Tglobal
Return times in the Netherlands
Return times in the Netherlands
El Niño?
Atlantic SST patterns?
Atlantic SST patterns?
Atlantic SST patterns?
Precipitation
doi:10.5194/hessd-12-13197-2015
December 2015 relative anomalies
Precipitation
1-dy precipitation in EC-Earth 2.3
1-dy precipitation in Weather@Home
Increase return times 1-dy precipitation N England
For a return time of O(100yr)
• Observations: 0.8–11 (+3%)
• Weather@Home: 1.05–1.4 (+4%)
• EC-Earth: 1.1–1.8 (+4%)
Large spread due to natural variability, but compatible. Clausius-Clapeyron scaling would give
~6.5%/K ⨉ ~0.5 K (upstream) ~ 4%.
El Niño?
El Niño?
El Niño?
Subpolar gyre?
Conclusions: return times• December temperatures were unusual in North
America and Europe, even taking the trend into account, with return times of hundreds of years.
• Northern England precipitation 1-day extremes were less unusual, with return times of tens of years.
• (Drought in the southern Europe was also quite strong, not yet investigated.)
Conclusions: drivers• The trend greatly enhanced the probability of mild
December, somewhat increased the probability of extreme precipitation in northern UK compatible with Clausius Clapeyron (~4% increase, 1.4 times more likely).
• El Niño had no discernible influence on the warm month but also made the precipitation extremes ~1.4 times more likely.
• We are investigating the role of Atlantic SST on the probability of extremes.
Thank you.
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