laurent kergoat (cnrs/lmtg, toulouse),
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Surface energy (and water) budget in the Sahel during the multi-decadal drought: combining remote sensing and in situ data. Laurent Kergoat (CNRS/LMTG, Toulouse), - PowerPoint PPT PresentationTRANSCRIPT
Surface energy (and water) budget in the Sahel during the multi-decadal drought: combining remote sensing
and in situ data.
Laurent Kergoat (CNRS/LMTG, Toulouse), Pierre Hiernaux, Françoise Guichard, Johanna Ramarohetra, Manuela Grippa, Franck Timouk, Eric Mougin and AMMA land surface and remote sensing groups(CEH, LTHE, HSM, LA)
Monitoring the Sahel droughtLargest multi decadal precipitation change, huge impact on population (water, food)
mean 350 mm
wet 50’ : pre drought
Data from DNM Mail
19842004
15°N, 1W
drought still important, maybe a recent trend towards recovery
3 debated questions
-1) Debate on positive feedback between surface and rainfall able (or not) to significantly strengthen monsoon anomaly
Vegetation decay increases surface albedo (and Rnet ?)Extremely few data
- 2) Debate greening or desertification ? Satellite series show a greening over 1982-present, Many studies point towards land degradation
-3) Debate on increased runoff in the Sahel: man-driven (crop area, woof cut) ?
Collection of results from the AMMA project (EU).Anyamba and Tucker 3005
Eddy fluxes and radiation stations networkvegetation, moisture...
9°40
13°4015°3017°
AMMA set up (starting 2005)
data from CEH, LMTG, HSM, LTHE, LA
60 km
The Hombori supersite : 3 main landscape units
June 06August 19
Seasonal cycle :sensible heat flux. Importance of surface runoff
Timouk et al. J. Hydrol. 2009
Evaluation of LSM: ALMIP exercisefair agreement for H flux but ....
Boones et al. BAMS 2009
Evaluation of satellite LandSAF and gewex-SRB products, ECMWF ISF and AMMA re-analysis
surface incoming radiationlarge overestimation of SWinc mainly due to dus (reverse for LW !)
Ramier et al. 2009
and ...ALMIP / GRACE significant differences in annual amplitude of soil moisture, partly due to dry season ETR.
Grippa et al 2010, WRR, in revisionALMIP 2 : mesoscale LSM model/data comparison, starting 2011 !
Surface net radiation for climate modelsAMMAMIP intercomparison (forced SST)
Hourdin et al BAMS 2010
OBS
too flat, large biases, even or mainly before the rain season !
Interannual variabilty : In situ and MODIS albedo
Satellite / in situ agreement on seasonal and interannual variability
Dramatic effect of the 2004 drought
Consistent with 1984-present difference in Meteosat albedo
(Latanziani and Govaerts, Eumetsat)Variability of the LW budget even more important ! (not shown)
Provides solid bases for feedback modeling (positive likely)
2004 drought
fire
Samain et al. JGR 2008
However, at decadal time scales, other processes become important« less rain, more water in ponds »
1966
1996
2007Gardelle et al., HESS, 2010
+ 100 increase in pond surface (n=91)
increase tree cover in valleys
On shallow soils, increased runoff, vegetation decay, soil erosion
2008
1954
shallow soils: Changes in Tin Adjar catchment, 16° N, 1954 - 2008
Ramarohetra 2010
CORONA. 15/10/1965 SPOT 28/12/03
2,25 6,52
11,65
37,26
41,44
0,8818,66
12,20
38,71
15,02
4,64
10,77
1954 2008
sand
rock trees
vegetated clayed valley
Decadal-scale effects of the Sahel drought:
sandy soil (65%): strong resilience of ecosystems (Hiernaux et al. 2009)complete recovery of trees and grassesconsistent with the ‘greening’ Sahel and rainfall
‘trend’
shallow soils (30 %)vegetation decay, triggered by the 1980’ droughtsincreased and concentrated runoff (gullies)important erosion. consistent with ‘degradation’. still decaying, completely climate driven in the Gourma !
lowlands, valleys, run-on areas (5%)spectacular increase of pond surface, large increase of trees coverconsistent with the greening Sahelcompletely cimate driven in the Gourma !
Decadal-scale effects of the Sahel drought:
Long-term effects on surface surface fluxes and water cycle
Delayed ETR cycle Rnet changes depending on both SW and LWdepending on plant cover changesdepending on soil erosion (and soil colour)more than an albedo story !
Involves threshold response of eco-hydrosystems to climatemay not be reversible (erosion)
Combines with land use changes (Southern Sahel)
Combines with dust emission and surface radiation budget
Thank you