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Abstract:This paper is addressed towards the problem of extracting appropriate model structures by systematic analysis of rainfall-runoff relationships in gauged catchments. The Upper Enns catchment in the Austrian Alps is selected as the basis of this study. The downward approach championed by Klemes is followed, which involves stepwise adjustment of model structure to capture the observed streamflow variability progressively at the annual, monthly, and then on to daily time scales. Throughout, we focus on emergent properties of the hydrological system at the various time scales, as detected in key signature plots and hydrographs, and model complexity is always kept to the minimum required. Any further alteration or calibration of parameter values is avoided, either with change of scales or in response to inadequate predictions. The downward approach presented leads to parsimonious water balance models with excellent performance and the minimum set of parameters, with a good balance being achieved between model performance and complexity.

Abstract. Risk zonation maps are mostly derived from design floods which propagate through the study area. The respective delineation of inundated flood plains is a fundamental input for the flood risk assessment of exposed objects. It is implicitly assumed that the river morphology will not vary, even though it is obvious that the river bed elevation can quickly and drastically change during flood events. The objectives of this study were to integrate the river bed dynamics into the flood risk assessment procedure and to quantify associated uncertainties. The proposed concept was applied to the River Ill in the Western Austrian Alps. In total, 138 flood and associated sediment transport scenarios were considered, simulated and illustrated for the main river stem. The calculated morphological changes of the river bed at the moment of peak flow provided a basis to estimate the variability of possible water surface levels and inundation lines which should be incorporated into flood hazard assessment. In the context of vulnerability assessment an advanced methodological approach to assess flood risk based on damage probability functions is described.

Abstract:In mountainous regions of mid latitudes, the accumulation and melting of snow plays an important role for the seasonal water balance. These processes not only exhibit a strong seasonality, but also a high spatial variability, which has to be accounted for when establishing distributed water balances in alpine environments. A methodology was developed for seasonal, spatially distributed modelling of accumulation and melting of snow and was embedded in a water balance model that uses only monthly values of precipitation and air temperature as meteorological input data. Hence, this methodology can also be applied in regions with limited data availability. The model uses a conceptual approach with a spatial resolution of a 1 km ð 1 km raster. Snow accumulation is computed from temperature and precipitation data. Snowmelt is computed with a temperature-index approach. A direct application of these simple concepts using monthly inputs would not yield satisfying results. Therefore, precipitation is disaggregated into rainfall and snowfall by using a transition range considering temporal variations of temperature within a month and the mean deviation of temperature on days with and without precipitation. For modelling snowmelt, two different approaches were tested to incorporate variable temperatures within a month. The model was applied for the whole of Austria (84 000 km 2 ) and simulated runoff was compared with observed runoff at 135 gauges for a 30 year period. The model performs best in high and medium mountainous catchments. Lower model performances are achieved in lowland catchments, where the contribution of snowmelt to river runoff decreases. It can be concluded that modelling accumulation and melting of snow in mountainous areas with monthly data yields good results if a temporal disaggregation of precipitation and temperature is applied.

This paper analyses the influence of climate change and land development on future flood risk for selected Austrian flood-prone municipalities. As part of an anticipatory micro-scale risk assessment we simulated four different inundation scenarios for current and future 100-and 300-year floods (which included a climate change allowance), developed scenarios of future settlement growth in floodplains and evaluated changes in flood damage potentials and flood risk until the year 2030. Findings show that both climate change and settlement development significantly increase future levels of flood risk. However, the respective impacts vary strongly across the different cases. The analysis indicates that local conditions, such as the topography of the floodplain, the spatial allocation of vulnerable land uses or the type of land development (e.g. residential, commercial or industrial) in the floodplain are the key determinants of the respective effects of climate change and land development on future levels of flood risk. The case study analysis highlights the general need for a more comprehensive consideration of the local determinants of flood risk in order to increase the effectiveness of an adaptive management of flood risk dynamics.