Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Continental-Scale Water-Balance Modelling of the Baltic and Other Large
Catchments
Elin Widén, Chong-yu Xu and Sven Halldin
Air and Water Science, Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, SWEDEN.
Corresponding author: Elin.Widen@hyd.uu.se
1. Introduction
Climate-change impact studies have primarily been
performed in developed, data-rich regions of the world.
There is a need to extend such studies to regions and seasons
where climate change is expected to show its largest impact,
i.e., high-latitude winter conditions and data-sparse regions
where man is living on sustainability margins. In this study,
we discuss the applicability at the continental scale of the
global-scale WASMOD-M model for simulation of
streamflow in present and future climates. The study
emphasises development of parameter-estimation schemes
and testing transferability of estimated parameters and
parameter-estimation schemes over regions and across
scales. The continental-scale applications will be performed
in a high-latitude, data-rich region (the Baltic-Sea
catchment) and a low-latitude, data-poor region (the Yellow-
River basin).
2. Existing models
Development of continental-scale hydrologic models has
been carried out at the world’s largest river basins. Two
types of macro-scale hydrological models are currently
being developed. The first type is the macro-scale waterbalance
model, MWB, (e.g., “Macro-PDM” of Arnell, 1999)
based on water-balance accounting. This type provides no
GCM-coupling and runs “off-line”. The second type is the
macroscale land-surface hydrological model, MHM, (e.g.
Figure 1. The Simplified flowchart of the WASMOD model system.
the VIC model of Liang et al., 1994) which aims at the
improvement of land-surface-hydrologic characteristics of
global-climate models, regional-climate models and mesoscale
meteorological models. Existing global hydrological
models tend to overestimate runoff in arid regions and
underestimate runoff in sub-arctic regions (e.g., Gerten
et al., 2003). Graham’s (2000) study with the HBV-Baltic
model represents one of the few hydrological-modelling
applications to the Baltic catchment.
Previous studies reveal that the main challenges remain in
(1) how to define the most useful physical characteristics,
(2) how to find successful regression equation for all
sensitive parameters and not just for some of them, (3)
how to test the transferability of regression equations from
catchment to regional scale and from sub-catchment
resolution to grid resolution, and to quantify the
uncertainty, and (4) how to verify model state variables in
a gridded model from observations of runoff and from
other observations.
3. WASMOD-M
Our global hydrological model, WASMOD-M (Waterand
Snow-Balance Modelling System at Macro-Scale) is a
further development of the catchment-scale WASMOD
(Xu, 2002). WASMOD (Figure 1) was taken as our
starting point since it works with a flexible time step (from
day to month), and can accept flexible input data