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          Institute: MPI für Meteorologie     Collection: Land in the Earth System     Display Documents



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ID: 499649.0, MPI für Meteorologie / Land in the Earth System
The effect of dynamic background albedo scheme on Sahel/Sahara precipitation during the Mid-Holocene
Authors:Vamborg, F.S.E.; Brovkin, V.; Claussen, M.
Language:English
Date of Publication (YYYY-MM-DD):2011
Title of Journal:Climate of the Past
Volume:7
Start Page:117
End Page:131
Review Status:Peer-review
Audience:Not Specified
Abstract / Description:We have implemented a new albedo scheme that takes the dynamic behaviour of the surface below the canopy into account, into the land-surface scheme of the MPI-ESM. The standard (static) scheme calculates the seasonal canopy albedo as a function of leaf area index, whereas the background albedo is a gridbox constant derived from satellite measurements. The new (dynamic) scheme additionally models the background albedo as a slowly changing function of organic matter in the ground and of litter and standing dead biomass covering the ground. We use the two schemes to investigate the interactions between vegetation, albedo and precipitation in the Sahel/Sahara for two time-slices: pre-industrial and mid-Holocene. The dynamic scheme represents the seasonal cycle of albedo and the correspondence between annual mean albedo and vegetation cover in a more consistent way than the static scheme. It thus gives a better estimate of albedo change between the two time periods. With the intro
duction of the dynamic scheme, precipitation is increased by 30mmyr(-1) for the pre-industrial simulation and by about 80mmyr(-1) for the mid-Holocene simulation. The present-day dry bias in the Sahel of standard ECHAM5 is thus reduced and the sensitivity of precipitation to mid-Holocene external forcing is increased by around one third. The locations of mid-Holocene lakes, as estimated from reconstructions, lie south of the modelled desert border in both mid-Holocene simulations. The magnitude of simulated rainfall in this area is too low to fully sustain lakes, however it is captured better with the dynamic scheme. The dynamic scheme leads to increased vegetation variability in the remaining desert region, indicating a higher frequency of green spells, thus reaching a better agreement with the vegetation distribution as derived from pollen records.
External Publication Status:published
Document Type:Article
Communicated by:Kauhs
Affiliations:MPI für Meteorologie/Land in the Earth System (2005-)
MPI für Meteorologie/IMPRS Earth System Modelling
Identifiers:DOI:10.5194/cp-7-117-2011
URL:http://www.clim-past.net/7/117/2011/cp-7-117-2011....
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