Consistency of observed winter precipitation trends in northern Europe with regional climate change projections

Jonas Bhend and Hans von StorchGKSS Research Institute, Geesthacht, Germany

Mastertitelformat bearbeiten

Motivation

> Gap between formal detection and attribution studies and “significant trends” studies

> Are the recent trends consistent with regional climate change projections?— Plausibility arguments— A priori assumption about the mechanism— Less informative than DnA but no estimate of natural variability

needed

Mastertitelformat bearbeiten

Data

> Observations:— CRU TS 2.1 monthly precipitation— 0.5° latitude-longitude grid

> Climate change scenarios:— RCAO simulations of the SMHI (PRUDENCE)— 0.44° rotated grid— Two different driving GCMs, HadAM3H and ECHAM4/OPYC3— Two emission scenarios SRES A2 and B2

— Four climate change scenarios defined as the difference between 1961-1990 and 2071-2100 mean

Mastertitelformat bearbeiten

Method

> Pattern correlation

S: Climate change signalO: Trends in observations

> Ratio of Intensities

with: and:

S 1

nSi2

i

PCC Si Oi

i

Si2

i

Oi2

i

O 1

nOi2

i

O

S

Mastertitelformat bearbeiten

Climate change scenarios...

Mastertitelformat bearbeiten

... and observations

Mastertitelformat bearbeiten

Pattern correlation

> Patterns are similar> Better correspondence with ECHAM scenarios> Better correspondence with stronger GHG forcing (A2)

Mastertitelformat bearbeiten

Sensitivity of PCCs

> Bootstrap with CRU precip fields— randomly select precip fields— compute trends— correlate trend fields

> Autocorrelation:moving blocks bootstrap, 5 years

Histogram of PCCs for the Baltic catchment (shaded) and northern Europe (hatched)

Mastertitelformat bearbeiten

Pattern correlation

> PCCs for the Baltic catchment significant> PCCs for all of northern Europe are not significant for HadAM B2

> Above findings robust to removal of the NAO

Mastertitelformat bearbeiten

Intensity

> Change in the observations much stronger than in scenarios

— RCM simulations are wrong— additional forcings— natural variability

Mastertitelformat bearbeiten

Mean change

> Change in the observations much stronger than in scenarios— RCM simulations are wrong— additional forcings— natural variability

Mastertitelformat bearbeiten

Different trend lengths

> PCCs decrease with increasing trend length> Significance levels are not affected by choice of trend length

> Intensity and mean change decrease with increasing trend length

Mastertitelformat bearbeiten

Conclusions - pattern correlation

> Baltic catchment:— Regional climate change scenarios are consistent— Observed and expected patterns are similar and significant

> Northern Europe:— Regional climate change scenarios are partly consistent— Pattern similarity with HadAM signal could be random

Mastertitelformat bearbeiten

Conclusions - intensity

> Both intensity and mean change suggest that:

> Assuming the model response to anthropogenic forcing is correct, a large part (30 to 70 percent) of the observed trends is due to other factors (e.g. natural variability).

Mastertitelformat bearbeiten

Thank you for your attention.