Impact of land use changes on extremes in the
ARPEGE-Climat model (LUCID experiment)
Aurore VOLDOIRE
CNRM, Toulouse, France
[email protected]
LUCID experiment
Aim of the LUCID project: Assessment of the impact of land-use
changes on climate
For past and future land-cover changes
On a multi-model basis
Experiments performed in CNRM
What is currently available ?
A pair of ensemble of simulations with prescribed SSTs
One with 1992 land cover
One with 1870 land cover
Each simulation consists of 31 years using SSTs over the period 1971-2001.
There are 5 elements for each case, each element differs by its initial
conditions.
Which model is used in CNRM ?
ARPEGE-Climat (v3) = the atmospheric component of CNRM-CM3 which
has been used in IPCC simulations
The land–surface scheme ISBA (Leaf Area Index -LAI- is prescribed)
Land cover maps
Percentage of crop area
(provided by N. DeNoblet)
1870
Vegetation fraction
in February
Anomaly 1992-1870
199
2
Vegetation fraction
in July
Anomaly 1992-1870
Vegetation parameters aggregated on the model grid(1)
February
Vegetation fraction
July
Vegetation parameters aggregated on the model grid(2)
Vegetation albedo
Soil depth
Impact on temperature and precipitations
2m Temperature
Precipitations
DJF
Isolines =
Student t-test
90% 95% 99%
JJA
Impact on total evaporation
Precipitation
Evaporation
DJF
Isolines =
Student t-test
90% 95% 99%
JJA
Relatively weak impact on hydrology in CNRM-CM3:
Is it the same for other models?
!!! Scale !!!
Regional land surface changes
Crops 25%  47%
Forests 47%  26%
Crops
Forests
10% 45%
58% 26%
Crops
1%  10%
Grasslands 39%  45%
Forests
48%  38%
Bare Soil
35%  25%
Grasslands 42%  53%
Forests
17%  12%
Crops
8%  27%
Grasslands 28%  21%
Forests
63%  51%
Bare Soil
68%  64%
Grasslands 24%  27%
US Great Plains: impact on monthly mean climate
Albedo
1870
1992
1992-1870
LAI
m2/m2
2m temperature
°C
Snow
Anomaly
1992-1870
%
kg.m-2
Vegetation fraction
US Great Plains: impact on monthly mean climate
+
%
Total evaporation
=
mm.d-1
% -1
mm.d
Vegetation fraction
Evapotranspiration
ISBA simulates a change in
evapotranspiration, but it is partly
compensated by an increase in bare soil
evaporation
Snow
kg.m-2
Anomaly
1992-1870
Soil Wetness Index
Precipitation
mm.d-1
-1
mm.d
m2/m2
Bare soil LAI
evaporation
1870
1992
1992-1870
Impact on daily variability and severe events
It has been shown in the case of tropical deforestation that landuse changes have a noticeable impact on daily variability
(Voldoire and Royer, 2004, Clim. Dyn.)
In the LUCID experiment, we propose to calculate Stardex
indices as in IPCC simulations (Frich et al., 2002, Clim. Res.)
Theses indices are based on daily P, Tmoy, Tmin and Tmax.
Maximum number of consecutive dry days
Precipitation intensity
Number of days with P>10mm.d-1
Number of frost days
Quantiles of Tmin and Tmax
…..
US Great Plains: impact on extremes? (1) temperature
1870
1992
1992-1870
°C
°C
Number of frost days
Tmax quantile 90%
Tmin quantile 90%
°C
Spread of
the anomaly
1992-1870
Tmax quantile 10%
Tmin quantile 10%
°C
°C
2m temperature
US Great Plains: impact on extremes? (2) precipitations
Precipitation intensity
mm.d-1
mm.d-1
Precipitation
Maximum number of
consecutive dry days
Number of days
with P>10mm.d-1
1870
1992
1992-1870
Conclusion
The impact of past land-use changes is the most noticeable
Over mid-latitudes
On temperature (snow masking effect of vegetation = –2°C in winter)
The impact on evaporation and precipitation is relatively weak
Because in ARPEGE-Climat the reduction in evapotranspiration is
compensated by an increase in evaporation from bare soil.
Is this compensation realistic? Do the other models involved in LUCID
produce the same effect?
Land-use changes have an impact on the daily distribution of
precipitations and temperatures. Stardex indices appear as a good
candidate to assess this question  we propose to calculate these
indices in all the LUCID experiments. Need to store daily Tmin,
Tmoy, Tmax and P.