ALBERT

Description: 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 × 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 km2) 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. Copyright © 2006 John Wiley & Sons, Ltd.

Description: To determine the distribution of water balance components in space and time, models are applied with a wide range of spatio-temporal discretizations - from lumped to distributed in the spatial scale and from annual to daily (or shorter) time-steps in the temporal scale. We present a comparative case study where we compare the simulation results of two conceptual water balance models using different spatio-temporal discretizations. Such a comparison enables to assess if different models with different discretizations may still yield similar results in space and time. The study focuses on the mountainous catchment of the river Gail (app. 1300 km2) in southern Austria for the period 1971-1990. The first model uses a semi-distributed discretization and daily data, whereas the second model uses a spatially distributed discretization (1 × 1 km raster) and monthly data. Both models use precipitation and temperature data as input. Parameters of the daily model were calibrated with runoff data of several gauges as part of a study focusing specifically on the Gail catchment. The distributed parameters of the monthly model were estimated regionally for establishing the water balance of the Hydrological Atlas of Austria. Both models perform equally well for runoff simulations. For simulation of temporal dynamics the models agree well for the main inputs and outputs of the system, with slightly lower agreements for sub-components - such as snowmelt for instance. In the spatial domain the correlation between the models is significantly lower. Differences are mainly related to different calibration approaches and are not dependent on the spatio-temporal discretization. Overall, the two water balance models yield consistent results, suggesting that the usage of monthly data is not inferior to the usage of daily data. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The need for estimates of distributed water balance in alpine catchments is addressed. Such estimates are an essential prerequisite for the efficient planning and management of water resource use. Specifically, the maximum appropriate spatial resolution that can be obtained in water balance estimates is assessed, given limited information of physiographic parameters and meteorological variables, in a complex topographical environment. This is done using a combination of existing modelling methodologies. The use of spatial disaggregation into subregions of similar climatic and topographic properties has been used as an optimal method for considering all stages of water balance estimation, from input data generation to model parameterization and water balance simulation. Various techniques for the spatial interpolation of precipitation and temperature point observations are evaluated in terms of their applicability to mountainous terrain, and external drift kriging is found to be the most suitable. A water balance model is introduced for an alpine catchment, capable of integrating dominant hydrological processes, for the computation of monthly and regional distributed water balances. The conceptual model is characterized by minimal model complexity, with most of the parameters estimated a priori from catchment physiography, in order to avoid an automatic model calibration. The hydrological water balance model is applied to the transboundary Gail river catchment, located between Austria and Italy, south of the main alpine divide. Copyright © 2005 John Wiley & Sons, Ltd.