Climate change and decadal variability of Chinese summer rainfall: a modelling study

Yonghui Lei, Brian Hoskins, Julia Slingo

and Andy Turner

Observed decadal variability in the period 1958-2007

Decadal variability in the period 1901-2002 using CRU dataset

Outline

Can HadCM3 simulate the observed decadal variability of Chinese summer rainfall without additional forcing?

• Changes in the mean state

• Changes in extreme

• Changes in variability

How may Chinese summer rainfall respond to doubled CO2 according to HadCM3?

Internal decadal variability in the 1000-year control run of HadCM3

Observation-like decadal variability identified in the 1000-year control run

Observation-like decadal variability in the 51-year period (the model year 590±25)

Regressions of surface temperature on decadal rainfall time series in the 51-year period

Regression on PC1 Regression on PC2

Can HadCM3 simulate the observed decadal variability of Chinese summer rainfall without additional forcing?

Yes!

• In general, internal decadal variability of Chinese summer rainfall is associated with decadal variability in the tropics.

• A particular 51-year period has remarkable similarity with observations in the recent 50 years for both Chinese summer rainfall and other large-scale variables.

Summary I

Changes in the climate of Chinese summer rainfall in the 2xCO2 run (I)

2xCO2

2xCO2

- control

percentage

Amount Intensity Frequency

Changes in the climate of Chinese summer rainfall in the 2xCO2 run (II)

Changes in the climate of Chinese summer rainfall in the 2xCO2 run (III)

Changes in extreme events of Chinese summer rainfall in the 2xCO2 run

Percentile (%)

mm/day

The dominant Chinese rainfall patterns in the control and 2xCO2 runs (I)

1xCO2 2xCO2

The dominant Chinese rainfall patterns in the control and 2xCO2 runs (II)

1xCO2 2xCO2 1xCO2 2xCO2

The dominant Chinese rainfall patterns in the control and 2xCO2 runs (III)

Uncertainty of decadal variability in the control and 2xCO2 runs (I)

Uncertainty of decadal variability in the control and 2xCO2 runs (II)

How may Chinese summer rainfall respond to doubled CO2 according to HadCM3?

Mean:

• Chinese summer rainfall increases, except the Yangtze River valley;

• Intensity increases everywhere;

• Decreases in the frequency over the east and increases over the northwest.

Summary II

How may Chinese summer rainfall respond to doubled CO2 according to HadCM3?

Summary II

Increases in extreme events, consistent with the Clausius-Clapeyron relationship

Variability:

• Increases in interannual variability are very likely with global warming, which may be associated with the strengthened El Nino events.

• Changes in decadal variability are unclear.