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| Titel |
The effect of a dynamic background albedo scheme on Sahel/Sahara precipitation during the mid-Holocene |
| VerfasserIn |
F. S. E. Vamborg, V. Brovkin, M. Claussen |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 7, no. 1 ; Nr. 7, no. 1 (2011-02-28), S.117-131 |
| Datensatznummer |
250004401
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| Publikation (Nr.) |
 copernicus.org/cp-7-117-2011.pdf |
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| Zusammenfassung |
| 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 introduction of the dynamic scheme, precipitation is
increased by 30 mm yr−1 for the pre-industrial simulation and by about
80 mm yr−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. |
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