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Abstract:
Terrestrial productivity in semi-arid woodlands is
strongly susceptible to changes in precipitation, and semiarid
woodlands constitute an important element of the global
water and carbon cycles. Here, we use the Carbon Cycle
Data Assimilation System (CCDAS) to investigate the key
parameters controlling ecological and hydrological activities
for a semi-arid savanna woodland site in Maun, Botswana.
Twenty-four eco-hydrological process parameters of a terrestrial
ecosystem model are optimized against two data streams
separately and simultaneously: daily averaged latent heat
flux (LHF) derived from eddy covariance measurements, and
decadal fraction of absorbed photosynthetically active radiation
(FAPAR) derived from the Sea-viewing Wide Field-ofview
Sensor (SeaWiFS).
Assimilation of both data streams LHF and FAPAR for
the years 2000 and 2001 leads to improved agreement between
measured and simulated quantities not only for LHF
and FAPAR, but also for photosynthetic CO2 uptake. The
mean uncertainty reduction (relative to the prior) over all parameters
is 14.9% for the simultaneous assimilation of LHF
and FAPAR, 8.5% for assimilating LHF only, and 6.1% for
assimilating FAPAR only. The set of parameters with the
highest uncertainty reduction is similar between assimilating
only FAPAR or only LHF. The highest uncertainty reduction
for all three cases is found for a parameter quantifying maximum
plant-available soil moisture. This indicates that not
only LHF but also satellite-derived FAPAR data can be used to constrain and indirectly observe hydrological quantities
