An extensive field measurement program in this small pre-alpine watershed was started in 1975. The general purpose of the program is to provide the data base for studies aiming to improve the understanding of all kinds of hydrological processes in an almost natural environment. The final aim of these studies is advanced modeling in the field of catchment hydrology. Standard instrumentation includes a weighable lysimeter, soil moisture probes and groundwater observation wells besides rain and river gauges, air temperature, humidity, and radiation sensors. Several temporary and specialized observation programs have been conducted so far and are further possible. Recent studies based on field data from the Rietholzbach basin deal with modeling of evapotranspiration within the system soil-vegetation-atmosphere and with water residence times and runoff generation in the catchment. In other projects, Rietholzbach data have been used as key information for watershed modeling in the view of possible water balance changes following expected climatic changes.
Spatially distributed hydrological modeling is an established tool in the simulation of the hydrological cycle. Pre-alpine and alpine catchments are characterized by highly variable morphology, soil and vegetation types and by great temporal and spatial variations in climatic elements. Hydrological models must consider a range of different types of hydrological systems. This requires tools for the assessment of interpolated meteorological variables as well as for the treatment of distributed geographical input data. Hydrological modeling of pre-alpine and alpine catchments has a long tradition at the IACETH. In the last ten years, two models have been developed for spatially distributed simulation of hydrological processes: WaSiM-ETH (Schulla 1997) and PREVAH (Gurtz et al. 1999). They are based on different conceptual methodologies, which allow their application to a wide variety of catchment conditions. An important basis for model development, calibration and validation was the research catchment Rietholzbach, which provides long term data records and allows various experimental studies in evapotranspiration (Menzel 1997) and runoff generation (Vitvar et al. 1999). This data set and those field studies allows a detailed parametrization and multiple validations of hydrological model components before their application in less equipped heterogeneous catchments.
Evapotranspiration and runoff, in particular, which are balanced by precipitation, constitute the land portion of the water cycle, which is known to be a main contributor to climate variability. Knowledge about these processes and the ability to realistically model them is therefore of central importance in climate research. There is, however, a gap between the local scale, at which land surface models and parameters are usually developed and evaluated, and the larger scales at which they are applied. This scale-gap can be bridged by integrating long-term hydrological and micrometeorological measurements (such as from Rietholzbach) with physically-based models of land surface-atmosphere exchanges. Additionally, the experimental data can be used as driver and validation tools in process-based analyses of model results.
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