10/04/2013 TU Delft Climate Institute Symposium: Do clouds change in a warming climate?

1. Jessica Loriaux, Geert Lenderink, Stephan de Roode
(Extreme) Precipitation, Present and Future
Pier Siebesma
TU Delft & KNMI
siebesma@knmi.nl

2. Clouds play a crucial role in weather and climate
• Radiation balance
• Hydrological cycle

3. Global Mean Precipitation
Observations (CMAP)
Multimodel mean (CMIP3)
Source: IPCC AR4 2007

4. The Role of Dynamics
Adler et al. JAMC 2012

5. 6Climate modeling
1.
Change of Global Precipitation
in a warming climate

6. Physical Basis (1) Clausius-Clayperon
2
ln
sds
s
TR
L
dT
ed
=
p
e
q s
s ε=
Saturation specific humidity:
For constant Relative Humidity RH=qv/qs :
specific humidity qv will increase with 6~7% per Kelvin
Constant RH hypothesis confirmed in many studies
for both models and observations:
i.e. Stephens (1990), Held and Soden (2006), Dai (2006)

7. Stephens and Ellis JCL 2006)
Global mean surface temperature vs water vapor amount for CMIP3 models: 1%/yr
increase CO2 runs
7.4 % increase per Kelvin
But what about Precipitation?

8. Global Precipitation increases with only 2~3% per Kelvin

9. Global Energy Controls on Precipitation
Global Atmospheric Energy Balance: LPSR atmnet +=,
Rnet,atm: net radiative loss from the atmosphere 97W/m2
P : Surface Precipitation 80W/m2
S : Surface Sensible Heat Flux 17W/m2
Relationships of the changes in a warming climate: PLSR atmnet ∆+∆=∆ ,
Increased radiative
cooling
Decrease in sensible
heat flux
Increase Precip
Global Precipitation increases in order to
compensate for the enhanced atmospheric
cooling.

10. Concluding Remarks
• Water vapor increases with ~7%/K following Clausius Clayperon
• Global Precipitation increases with 2~3%/K
•The lower growth rate of precipitation can be attributed to the relation
between the enhanced (clear sky) radiative cooling and the increased water
vapor (“the curve of growth”) (i.e. Stephens and Ellis 2008, Lambert and Webb
2008)
• The different temperature relations for water vapor and precipitation has
the consequence that the atmospheric branch of the hydrological cycle is
slowing down.
But what about the geographical distribution of Precipitation Changes?

11. Models ΔP [IPCC 2007 WGI] for A1B scenario
(IPCC 2007)
Do the rich get richer? (Held and Soden 2006)
Is there a contrasting precipitation responses in wet and dry regions?
Some limited observational evidence, e.g. Zhang et al. (2007) Nature
Netherlands on the borderline between mean positive/negative response

12. 13Climate modeling
2.
Change of (Extreme) Precipitation in a
warming climate in the Netherlands

13. Climatology of mean summer precip in the Netherlands
Figure: 20-year moving average of mean,
coastal and inland precipitation for summer in
the Netherlands (Lenderink et al. 2008).

14. Figure: 20-year moving average of mean,
coastal and inland precipitation for summer in
the Netherlands (Lenderink et al. 2008).
 Trend in the growth of the inland-
coastal precipitation difference.
 Due to warmer sea surface
temperatures
But what about extreme precipitation?
Climatology of mean summer precip in the Netherlands

15. observations
• Take the de 90%, 99% , 99,9% percentiles of the most extreme precipitation sums
• Group them as a function of the (dewpoint) temperature.
• Use this (dewpoint) temperature as a proxy of how extreme precipitation changes in
a warming climate.
Loriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)
KNMI Precipitation Data Set: • 27 stations in the Netherlands:
• daily dataset: 1980-2010
• 10 min dataset: 2003-2011

16. Daily Precip Sum
7% increase per degree
Td
Precipintensity(mm/day)
99.9%
99%
90%
observations
Loriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)

17. Daily Precip Sum
7% increase per degree
Td
Precipintensity(mm/day)
99.9%
99%
90%
observations
Loriaux, Lenderink, Siebesma & de Roode (submited JCL 2013)
Td
14% increase per degree
10 Minutes sum
Large Scale Precip Convective Showers

18. Interpretation of the Results
• Intuitively CC-scaling can be understood by assuming that the extreme cases are
those in which the available water vapor gets squeezed out of the atmosphere
effectively.
•But what about super CC scaling?
• Latent heat release creates buoyancy
• buoyancy is transformed into kinetic energy
• Resulting increasing vertical velocity induces
convergence.
•Convergence is an extra source for moisture






∂
∂
=
∂
∂
≈ ∫ z
q
wdz
z
q
wP s
z
z
st
b
Simple updraft model:
w

19. The Experiment

20. For each temperature perturbation calculate the fractional increase of precipation:




∂
∂




∂
∂
=
z
q
w
z
q
w
P
P
s
s
δ
δ
And break it down in a thermodynamic and a dynamical part:
( )




∂
∂




∂
∂
+




∂
∂




∂
∂
=
z
q
w
z
q
w
z
q
w
z
q
w
P
P
s
s
s
s
δδ
δ
Thermodynamic
part
Dynamical
part

22. Precipitation
Heavy frontal rain follows moisture (~7%/K)
Mean Precipitation linked to
radiation balance (~3%/K)
Light Precipitation (-?%/K)
Temperature 
Heavy
Convective
Rain
(14%
/K)
Summary:
Free after Richard Allen
Univ. Of Reading