LUCIDLand-Use and Climate: IDentification of robust impacts

Nathalie de Noblet, Andy Pitman

nathalie.de-noblet@cea.fr

40% of the land is nowadays intensively used for anthropogenic

activities

Maps obtained combining 2 datasets:

Ramankutty & Foley (1999),

Goldewijk (2001)

Fraction of each 1°*1° grid-cell occupied by

crops

year 1700

Year 1992

Has (will) the perturbation of biophysical

variables and of fluxes exchanged at the

land/atmosphere interfaceinduced by the anthropogenic land-cover changes

in a context where atmospheric CO2 is increasing

significantly modified (modify)

atmospheric and/or oceanic circulation?

Foley, 2003

50 100 150 200 250 300 3500

1

2

3

4

5

6LAI : Indice Foliaire

days50 100 150 200 250 300 350

0

1

2

3

4

5

6LAI : Indice Foliaire

days

a different partitioning

of energy and water

a change in the

timing of the

seasonal cycle

winter crop

natural grassland

Gervois et al. 2005

-0,5

0

0,5

1

1,5

augmentation du CO2 utilisation des sols

+ 1,5 W/m2 - 0,26 W/m2

From pre-industrial times

Contribution to the global radiatif forcinga) CO2 (red) and b) land-surface albedo (green)

PhD Edouard Davin (in progress)

We know (1)

from meso-scale studies

that

land-use induced land-cover changeshave a large impact on

the meso-scale atmospheric circulations

in 1993, natural wetlands are replaced by crops in South Florida

Marshall et al., Nature 2003

in 1997, a rare freeze inflicted severe damage in these new

agricultural regionsHas the conversion of wetlands increased the incidence and severity of damaging freezes?

Natural vegetationPre-1900

Actual vegetationPost-1993

Regional atmosphericmodel - RAMS

Region atmosphericmodel - RAMS

Differences

Changes in biophysicalparameters of the land

Effect of land-use induced land-cover changes on temperature and duration of

below-freezing events

Marshall et al., Nature 2003

Temperatures are colderafter having drained the wetlands

°C minutes

Longer duration ofbelow-freezing events

We know (2)

from large-scale studies

using models of intermediate complexity

that

biophysical impacts of land-use inducedland-cover changes have cooled down the climate,

partially counteracting the effectsof increasing atmospheric CO2

Many models of intermediate complexity have seen the same deforestation scenarios over the past 1000 years

in all models: deforestation global and annual cooling of the northern

hemisphere

Brovkin et al., Climate Dynamics 2006

This global cooling mainly comes from the high latitudes,and results from an increased surface albedo

zonal + annual meansurface temperature (°C)

zonal mean surface albedo

Brovkin et al., Climate Dynamics 2006

During this same time period, atmospheric CO2 increases

CO2

and leads to the well-known ‘climate warming’

Brovkin et al., Climate Dynamics 2006

The combined effects of deforestation and increased CO2

have led to a cooling until ~1900 followed by a warming

Brovkin et al., Climate Dynamics 2006

But there is no consensus on

the magnitude of the global scale cooling

the spatial distribution of that global scale cooling

the potential changes induced on modes of atmospheric variability, extremes, interannual and decadal variability

+ all (except Hadley Centre) simulations within IPCC AR4

do not account for

land-use induced land-cover changes

So we have decided to start a model intercomparison project (MIP)

snap-shot experiments (pre-industrial and present-day) forced with the same observed SSTs, SICs, CO2 and crop/pasture distribution

ensemble simulations (6 to 10 members)

transient simulations from 1870 to 2002 forced with the same observed SSTs, SICs, CO2 and crop/pasture distribution (within the C20C project)

transient simulations from 1850 till 2100 with computed SSTs and SICs (within the European ENSEMBLES project)

Project endorsed by

IGBP – iLEAPS

And

GEWEX-GLASS

So far6 groups have started to run some or all experiments:

Meteo-France (Aurore Voldoire) … all LSCE (Nathalie de Noblet) … all Macquarie University (Andy Pitman) … snapshots Université de Montpellier (Christine Delire) … snapshots NCAR (Gordon Bonan) … all COLA (Maggie Zhao) … transient with prescribed SSTs (C20C)

set-up a distribution list and a DODS serverlucid@dsm-mail.saclay.cea.fr

http://dods.extra.cea.fr/data/p25nath/DIVA/ForcingData/

written a first draft of the protocol … there are still some open questions (merging of crop/pasture map with each model’s land-cover map; leaf area index prescribed in some models, computed in others!, some models still are not able to update their land-

cover map regularly/yearly…)