 |
| Titel |
Is soil moisture initialization important for seasonal to decadal predictions? |
| VerfasserIn |
Tobias Stacke, Stefan Hagemann |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089323
|
| Publikation (Nr.) |
 EGU/EGU2014-3523.pdf |
|
|
|
|
|
| Zusammenfassung |
| The state of soil moisture can can have a significant impact on regional climate conditions for
short time scales up to several months. However, focusing on seasonal to decadal time scales,
it is not clear whether the predictive skill of global a Earth System Model might be enhanced
by assimilating soil moisture data or improving the initial soil moisture conditions with
respect to observations.
As a first attempt to provide answers to this question, we set up an experiment to
investigate the life time (memory) of extreme soil moisture states in the coupled
land-atmosphere model ECHAM6-JSBACH, which is part of the Max Planck Institute for
Meteorology’s Earth System Model (MPI-ESM). This experiment consists of an ensemble of
3 years simulations which are initialized with extreme wet and dry soil moisture states
for different seasons and years. Instead of using common thresholds like wilting
point or critical soil moisture, the extreme states were extracted from a reference
simulation to ensure that they are within the range of simulated climate variability. As a
prerequisite for this experiment, the soil hydrology in JSBACH was improved by
replacing the bucket-type soil hydrology scheme with a multi-layer scheme. This
new scheme is a more realistic representation of the soil, including percolation
and diffusion fluxes between up to five separate layers, the limitation of bare soil
evaporation to the uppermost soil layer and the addition of a long term water storage
below the root zone in regions with deep soil. While the hydrological cycle is not
strongly affected by this new scheme, it has some impact on the simulated soil
moisture memory which is mostly strengthened due to the additional deep layer water
storage.
Ensemble statistics of the initialization experiment indicate perturbation lengths between
just a few days up to several seasons for some regions. In general, the strongest effects are
seen for wet initialization during northern winter over cold and humid regions, while the
shortest memory is found during northern spring. For most regions, the soil moisture memory
is either sensitive to wet or to dry perturbations, indicating that soil moisture anomalies
interact with the respective weather pattern for a given year and might be able to enhance
or dampen extreme conditions. To further investigate this effect, the simulations
will be repeated using JSBACH with prescribed meteorological forcing to better
disentangle the direct effects of soil moisture initialization and the atmospheric response. |
|
|
|
|
|
|