Large-Scale Hydrology in Europe : Observed Patterns and Model Performance
Appears in the following Collection
- Institutt for geofag 
AbstractIn a changing climate, terrestrial water storages are of great interest as water availability impacts key aspects of ecosystem functioning. Thus, a better understanding of the variations of wet and dry periods will contribute to fully grasp processes of the earth system such as nutrient cycling and vegetation dynamics. Currently, river runoff from small, nearly natural, catchments is one of the few variables of the terrestrial water balance that is regularly monitored with detailed spatial and temporal coverage on large scales. River runoff, therefore, provides a foundation to approach European hydrology with respect to observed patterns on large scales, with regard to the ability of models to capture these.
The analysis of observed river flow from small catchments, focused on the identification and description of spatial patterns of simultaneous temporal variations of runoff. These are dominated by large-scale variations of climatic variables but also altered by catchment processes. It was shown that time series of annual low, mean and high flows follow the same atmospheric drivers. The observation that high flows are more closely coupled to large scale atmospheric drivers than low flows, indicates the increasing influence of catchment properties on runoff under dry conditions. Further, it was shown that the low-frequency variability of European runoff is dominated by two opposing centres of simultaneous variations, such that dry years in the north are accompanied by wet years in the south.
Large-scale hydrological models are simplified representations of our current perception of the terrestrial water balance on large scales. Quantification of the models strengths and weaknesses is the prerequisite for a reliable interpretation of simulation results. Model evaluations may also enable to detect shortcomings with model assumptions and thus enable a refinement of the current perception of hydrological systems. The ability of a multi model ensemble of nine large-scale hydrological models and the land surface scheme of a high resolution regional climate model to capture various aspects of runoff were assessed. In general high and mean flows were better captured than low flows, pointing toward deficiencies with the models representation of storage processes. The analysis of the multi model ensemble also showed that the mean of all model simulations generally provided a more robust and accurate estimator of continental scale variations of catchment runoff than any individual model. List of papers. Papers I and III-V are removed from the thesis due to copyright restrictions.
Paper I: Lukas Gudmundsson, Lena M. Tallaksen and Kerstin Stahl Spatial cross-correlation patterns of European low, mean and high flows Hydrological Processes, 2011, 25, 1034 – 1045. doi:10.1002/hyp.7807
Paper II: Lukas Gudmundsson, Lena M. Tallaksen, Kerstin Stahl and Anne K. Fleig Low-frequency variability of European runoff Hydrology and Earth System Sciences Discuss., 8, 1705-1727, 2011 doi:10.5194/hessd-8-1705-2011 Published under a Creative Commons Attribution License.
Paper III: Lukas Gudmundsson, Lena M. Tallaksen, Kerstin Stahl, Douglas B. Clark, Egon Dumont, Stefan Hagemann, Nathalie Bertrand, Dieter Gerten, Naota Hanasaki, Jens Heinke, Frank Voß and Sujan Koirala Comparing Large-scale Hydrological Models to Observed Runoff Percentiles in Europe Journal of Hydrometeorology 2012, 13, 604–620. doi:10.1175/JHM-D-11-083.1
Paper IV: Lukas Gudmundsson, Thorsten Wagener, Lena M. Tallaksen and Kolbjørn Engeland Seasonal Evaluation of Nine Large-Scale Hydrological Models Across Europe Manuscript version, published as: Evaluation of nine large-scale hydrological models with respect to the seasonal runoff climatology in Europe. Water Resources Research Volume 48, Issue 11, November 2012 doi:10.1029/2011WR010911
Paper V: Kerstin Stahl, Lena M. Tallaksen, Lukas Gudmundsson and Jens H. Christensen Streamflow data from small basins: a challenging test to high resolution regional climate modeling Journal of Hydrometeorology 2011 ; 12, 900–912. doi:10.1175/2011JHM1356.1