2 research outputs found
Does the Danube exist? Versions of reality given by various regional climate models and climatological datasets
We present an intercomparison and verification analysis of several regional
climate models (RCMs) nested into the same run of the same Atmospheric Global
Circulation Model (AGCM) regarding their representation of the statistical
properties of the hydrological balance of the Danube river basin for 1961-1990.
We also consider the datasets produced by the driving AGCM, from the ECMWF and
NCEP-NCAR reanalyses. The hydrological balance is computed by integrating the
precipitation and evaporation fields over the area of interest. Large
discrepancies exist among RCMs for the monthly climatology as well as for the
mean and variability of the annual balances, and only few datasets are
consistent with the observed discharge values of the Danube at its Delta, even
if the driving AGCM provides itself an excellent estimate. Since the considered
approach relies on the mass conservation principle and bypasses the details of
the air-land interface modeling, we propose that the atmospheric components of
RCMs still face difficulties in representing the water balance even on a
relatively large scale. Their reliability on smaller river basins may be even
more problematic. Moreover, since for some models the hydrological balance
estimates obtained with the runoff fields do not agree with those obtained via
precipitation and evaporation, some deficiencies of the land models are also
apparent. NCEP-NCAR and ERA-40 reanalyses result to be largely inadequate for
representing the hydrology of the Danube river basin, both for the
reconstruction of the long-term averages and of the seasonal cycle, and cannot
in any sense be used as verification. We suggest that these results should be
carefully considered in the perspective of auditing climate models and
assessing their ability to simulate future climate changes.Comment: 25 pages 8 figures, 5 table
Hydrological cycle in the Danube basin in present-day and XXII century simulations by IPCCAR4 global climate models
We present an intercomparison and verification analysis of 20 GCMs (Global
Circulation Models) included in the 4th IPCC assessment report regarding their
representation of the hydrological cycle on the Danube river basin for 1961–2000
and for the 2161–2200 SRESA1B scenario runs. The basin-scale properties of the
hydrological cycle are computed by spatially integrating the precipitation, evaporation,
and runoff fields using the Voronoi-Thiessen tessellation formalism. The span of the
model- simulated mean annual water balances is of the same order of magnitude of
the observed Danube discharge of the Delta; the true value is within the range
simulated by the models. Some land components seem to have deficiencies since there
are cases of violation of water conservation when annual means are considered. The
overall performance and the degree of agreement of the GCMs are comparable to those
of the RCMs (Regional Climate Models) analyzed in a previous work, in spite of the
much higher resolution and common nesting of the RCMs. The reanalyses are shown
to feature several inconsistencies and cannot be used as a verification benchmark for
the hydrological cycle in the Danubian region. In the scenario runs, for basically all
models the water balance decreases, whereas its interannual variability increases.
Changes in the strength of the hydrological cycle are not consistent among models:
it is confirmed that capturing the impact of climate change on the hydrological cycle
is not an easy task over land areas. Moreover, in several cases we find that qualitatively
different behaviors emerge among the models: the ensemble mean does not represent
any sort of average model, and often it falls between the models’ clusters