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Veröffentlichungen aus dem Verbundvorhaben KliMoBay

Investigation and Comparison of Suitable Approaches to Estimate Actual Evapotranspiration as a Major Component of the Water Balance in Peatlands

Adriane Hoevel 2021, Lehrstuhl für Hydrologie und Flussgebiets­management,Technische Universität München, Masterarbeit

In this thesis, a variety of methods to estimate actual evapotranspiration (ETA) from peatlands as a major water balance component have been investigated and compared within the framework of the KliMoBay (Klimaschutz- und Anpassungspotentiale in Mooren Bayerns) project at the Chair of Hydrology and River Basin Management (TUM). As a first step, the current state of research on evapotranspiration from peatlands has been analyzed as part of an extended literature review. It emerged that although methods developed specifically for peatlands do exist, for instance the Romanov method, more general and commonly known approaches such as the Penman-Monteith method are still used to a larger extent. A high share of studies found that methods of Penman-Monteith or Priestley-Taylor are able to reproduce measured evapotranspiration well if defining parameters within the governing equations have been calibrated site-specifically.
A hydrological model has consequently been applied to a selected study area in southern Bavaria, namely the Schechenfilz peatland site, in order to assess similarities and differences in simulated ETA rates with different methods. Since measurements of latent heat flux were available for the regarded area, modeling results could additionally be evaluated in terms of their ability to reproduce measured evapotranspiration. Prior to setting up the model, a sensitivity analysis has been conducted in order to estimate the model’s sensitivity to changing input parameters. It has been assessed that the model is rather sensitive to an alteration of climate input data, especially sunshine duration, than to a change of defining input parameters such as vegetational characteristics or specific peatland properties.
Based on the findings of the sensitivity analysis, the hydrological model representing the Schechenfilz peatlands has been set up with different evapotranspiration estimation methods. Simulation results show that actual evapotranspiration differs to a high extent between methods, especially with regard to the four meteorological seasons. When comparing modelled to measured ETA, mean annual simulated rates deviate from measurements differently for each applied method. However, the Romanov method specifically developed for peatland yields the smallest deviation with overall -7.6% with regard to the long-term mean annual ETA, followed by Penman-Monteith with a difference of +9.8%. Besides uncertainty in input data including defining parameters as well as measured meteorological data, it is not sure whether obtained outcomes can be transferred to other peatlands in Bavaria. In the future, additional case studies which optimally include a validation with groundwater measurements as well must be realized to reduce uncertainty in modeled ETA from peatland environments.