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.