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Study region: Tisza and Prut catchments, originating on the slopes of the Carpathian mountains. Study focus: The study reported here investigates (i) climate change impacts on flood risk in the region, and (ii) uncertainty related to hydrological modelling, downscaling techniques and climate projections. The climate projections used in the study were derived from five GCMs, downscaled either dynamically with RCMs or with the statistical downscaling model XDS. The resulting climate change scenarios were applied to drive the eco-hydrological model SWIM, which was calibrated and validated for the catchments in advance using observed climate and hydrological data. The changes in the 30-year flood hazards and 98 and 95 percentiles of discharge were evaluated for the far future period (2071-2100) in comparison with the reference period (1981-2010). New hydrological insights for the region: The majority of model outputs under RCP 4.5 show a small to strong increase of the 30-year flood level in the Tisza ranging from 4.5% to 62%, and moderate increase in the Prut ranging from 11% to 22%. The impact results under RCP 8.5 are more uncertain with changes in both directions due to high uncertainties in GCM-RCM climate projections, downscaling methods and the low density of available climate stations.
Floods and debris flows in small Alpine torrent catchments (<10km(2)) arise from a combination of critical antecedent system state conditions and mostly convective precipitation events with high precipitation intensities. Thus, climate change may influence the magnitude-frequency relationship of extreme events twofold: by a modification of the occurrence probabilities of critical hydrological system conditions and by a change of event precipitation characteristics. Three small Alpine catchments in different altitudes in Western Austria (Ruggbach, Brixenbach and Langentalbach catchment) were investigated by both field experiments and process-based simulation. Rainfall-runoff model (HQsim) runs driven by localized climate scenarios (CNRM-RM4.5/ARPEGE, MPI-REMO/ECHAM5 and ICTP-RegCM3/ECHAM5) were used in order to estimate future frequencies of stormflow triggering system state conditions. According to the differing altitudes of the study catchments, two effects of climate change on the hydrological systems can be observed. On one hand, the seasonal system state conditions of medium altitude catchments are most strongly affected by air temperature-controlled processes such as the development of the winter snow cover as well as evapotranspiration. On the other hand, the unglaciated high-altitude catchment is less sensitive to climate change-induced shifts regarding days with critical antecedent soil moisture and desiccated litter layer due to its elevation-related small proportion of sensitive areas. For the period 2071-2100, the number of days with critical antecedent soil moisture content will be significantly reduced to about 60% or even less in summer in all catchments. In contrast, the number of days with dried-out litter layers causing hydrophobic effects will increase by up to 8%-11% of the days in the two lower altitude catchments. The intensity analyses of heavy precipitation events indicate a clear increase in rain intensities of up to 10%.
Entlang der Küstenniederung des Naturschutzgebietes „Hütelmoor und Heiligensee“, ca. 6 km nordöstlich von Rostock-Warnemünde gelegen, wird seit dem Jahr 2000 die Küstendüne nicht mehr instand gehalten. Im Rahmen der Renaturierung des Gebietes werden so grundsätzlich wieder Überflutungen bei Ostseehochwassern zugelassen, was bisher jedoch noch nicht eingetreten ist. Am 4./5. Januar 2017 ereignete sich ein Sturmhochwasser der Ostsee, mit einem Scheitelwasserstand in Warnemünde, der sich zwischen dem 10- und 20-jährlichen Hochwasserstand einordnet. Dennoch kam es bei diesem Ereignis nicht zum Dünendurchbruch und zur seeseitigen Überflutung, wohl aber zum binnenseitigen Einstrom von Salz- bzw. Brackwasser. Dieser erfolgte über den Graben, durch den das Gebiet normalerweise über die Warnow in die Ostsee entwässert. Durch das Einströmen über die Sohlschwelle, sonst Auslass des Gebietes, stiegen die Wasserstände und Salzkonzentrationen in der südwestlichen Hälfte der Niederung an. Mit zunehmender Entfernung zur Sohlschwelle waren diese Auswirkungen jedoch geringer spürbar. Dies gilt wegen der Retentionswirkung der Niederung mehr für den Wasserstand als für die Salzkonzentration. Während der Wasserstand durch den Einstau der Niederung und Überschwemmungen flächenhaft anstieg, breitete sich die Salzfront präferentiell in den ehemaligen Entwässerungsgräben, die trotz des Einstaus nach wie vor hydraulisch aktiv sind, eher linienhaft aus. Diese Interpretation beruht auf Messergebnissen von Wasserstand, elektrischer Leitfähigkeit und Wassertemperatur.
An ensemble of 10 hydrological models was applied to the same set of land use change scenarios. There was general agreement about the direction of changes in the mean annual discharge and 90% discharge percentile predicted by the ensemble members, although a considerable range in the magnitude of predictions for the scenarios and catchments under consideration was obvious. Differences in the magnitude of the increase were attributed to the different mean annual actual evapotranspiration rates for each land use type. The ensemble of model runs was further analyzed with deterministic and probabilistic ensemble methods. The deterministic ensemble method based on a trimmed mean resulted in a single somewhat more reliable scenario prediction. The probabilistic reliability ensemble averaging (REA) method allowed a quantification of the model structure uncertainty in the scenario predictions. It was concluded that the use of a model ensemble has greatly increased our confidence in the reliability of the model predictions.
Approximation of Groundwater - Surface Water - Interactions in a Mesoscale Lowland River Catchment
(2004)
Advances in Flood Research
(2002)