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Dynamical coupling of the HIRHAM regional climate model and the MIKE
SHE hydrological model
Martin Drews 1 , Søren H. Rasmussen 1 , Jens Hesselbjerg Christensen 1 , Michael B. Butts 2 , Jesper
Overgaard 2 , Sara Maria Lerer 2 and Jens Christian Refsgaard 3
1 Danish Meteorological Institute, Lyngbyvej 100, DK-2100 Copenhagen E, Denmark, mad@dmi.dk
2 DHI Water and Environment, Agern Alle 11, DK-2970, Hørsholm, Denmark
3 Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
Introduction
Traditionally, the hydrological impacts of climate change
have been based on driving hydrological models with the
output of global or regional climate models, e.g. Graham et
al. (2007). This means that the feedbacks to the atmosphere
are neglected, which has an unknown impact on the
predictions of climate change, particularly at the local scale.
Furthermore, climate models often operate at spatial and
temporal scales that are much larger than the scales required
for analyzing the effects on the hydrological system. This
means that the representation of the hydrology in these
climate models is often very simplified and therefore not
suitable for detailed hydrological analyses.
To develop improved methods for assessing the effects of
climate change on water resources, a fully coupled
hydrological and climate modelling system is being
developed using two state-of-the-art model codes: the
climate model code HIRHAM, Christensen et al. (1996), and
the hydrological model code MIKE SHE, Graham and Butts
(2006) The coupling will exploit new OpenMI technology
that has recently emerged from the water sector for coupling
model components. OpenMI provides a standardized
interface to define, describe and transfer data on a time basis
between software components that run simultaneously thus
supporting systems where feedback between the modelled
processes is necessary, Gregersen et al. (2007). Therefore,
OpenMI is ideally suited to linking hydrological and climate
models and allows linking with different spatial and
temporal representations and across different platforms. This
new technology will also be effective in linking the
meteorological and hydrological modelling communities.
MIKE SHE
MIKE SHE is an advanced, flexible framework for
hydrologic modeling, Butts et al., (2004); Graham & Butts
(2006). MIKE SHE covers the major processes in the
hydrological cycle and includes process models for
evapotranspiration, overland flow, unsaturated flow,
groundwater flow, and channel flow and their interactions.
Each of these processes can be represented at different levels
of spatial distribution and complexity according to the goals
of the modelling study, the availability of field data and the
modeller’s choices, Butts et al. (2004).
A new energy-based evapotranspiration model has been
implemented in MIKE SHE, Overgaard et al. (2007), and
will be used to model the feedback processes between the
land surface and atmosphere. This new evapotranspiration
model was successfully evaluated against observations of
energy fluxes collected during the First International
Satellite Land Surface Climatology Project (ISLSCP) Field
Experiment (FIFE). FIFE was conducted in a 15x15 km area
near Manhattan, Kansas, in and around the Konza Prairie.
HIRHAM
HIRHAM is a regional atmospheric climate model, cf.
Christensen et al. (1996), based on a subset of the
HIRLAM, cf. Undén et al. (2002) and ECHAM models,
cf. Roeckner et al. (2003), combining the dynamics of the
former model with the physical parameterization schemes
of the latter. A new and updated version, HIRHAM5, has
recently been developed in collaboration between the
Danish Meteorological Institute and the Potsdam Research
Unit of the Alfred Wegener Institute Foundation for Polar
and Marine Research and was released in 2006, cf.
Christensen et al. (2006).
Coupling scheme
The coupling will be made such that HIRHAM’s standard,
simple land surface parameterization scheme
(hydrological model) will be utilized in regions not
covered by the MIKE SHE model. This will make it
possible to apply the coupled code without having to set
up MIKE SHE on the entire regional scale covered by
HIRHAM, and it will therefore save both personal time
and computational power. The following parameters are
passed from the climate model to the hydrological model:
air temperature, precipitation, wind speed, relative
humidity, global radiation, and air pressure, whereas
sensible and latent heat flux and surface temperature is
passed to the climate model.
Since the HIRHAM code is designed to run efficiently on
a massively parallel UNIX/LINUX system, while MIKE
SHE runs primarily on a WINDOWS PC, a critical task is
to develop a suitable method for cross-platform
communication, i.e. in order to facility the exchange of
parameters at run-time. Here, we exploit the OpenMI
standard interface technology. In brief, an OpenMI
compliant version of MIKE SHE has been built to run on a
WINDOWS PC along with a similarly compliant “proxy”
version of the HIRHAM model. The proxy component is
linked to a HIRHAM wrapper on the UNIX/LINUX side,
which implements the smallest subset of the OpenMI
standard methods and provides a direct interface to the
modified model code. In this way any of the model
components, i.e. HIRHAM or MIKE SHE, may be
seamlessly exchanged or new ones added, e.g. to build a
regional Earth system model.
Concluding remarks
This poster presentation provides further details on the
coupled model system and the OpenMI interface. Also, we
present preliminary results from coupled feasibility studies
carried out on the basis of data from the FIFE project as
well as reanalysis data from the CRU and ERA-40
archives.