Diploma Thesis

Modellierung des Kohlenstoff- und Energieaustausches am Waldstein/Weidenbrunnen im Jahr 2003

Andreas Schäfer (03/2009-06/2010)

Support: Thomas Foken, Katharina Köck (Staudt)

As only shorter time periods have been simulated with the ACASA model so far, the aim of this diploma thesis is to evaluate the carbon- and energy-exchange modelling for the FLUXNET station Waldstein-Weidenbrunnen over a one-year period. In general, especially years with extreme climatic conditions are of great interest for the evaluation of ecosystem models, particularly with regard to the climate change. For this reason, the year of 2003 was the object of investigation for this thesis as nearly the whole of Europe had been influenced by a heat wave during the summer months (Schaer et al. 2004). Concerning this, the thesis put the question how these special climatic conditions could have had an impact on the net ecosystem exchange, the net radiation, the soil heat flux and the turbulent fluxes. To evaluate the modelling quality over the period of a year, the results were analized on timescales of monthly means and time series of individual days. In this process it emerged that ACASA is able to reproduce the actual measured values for net radiation with an agreement of 99-100% (index of agreement) almost over the whole year, except for snow periods. Within these periods it could be seen that ACASA modelled different snow layer dynamics at the same time. Consequentially there were significant differences in simulated soil heat fluxes. In this context, much higher modelling results than measurements could be seen during the analysis of the soil temperature in summer. Therefore the soil module calculations were discovered as a weak point of the ACASA model. The sensible heat flux modelling showed an agreement of 73% over the whole year, which could be improved to 89% by closing the measurements’ energy balance. The only exception was the hottest month of the year, August, which had mean monthly temperatures of 19.1 °C (+5.4 °C in comparison to the long term mean of 1961-1990). In this month, the mean sensible heat flux was underestimated by ACASA and, at the same time, the latent heat flux was overestimated. By closing the energy balance of the measurements in general, the agreement of the mean latent heat flux with the simulated results could be improved from 44% to 66%. But by doing so, the comparatively strong agreement within the mean daily cycle of latent heat flux in the months of June and July changed into an underestimation by ACASA. Though there was a stronger agreement within the daily cycles of the sensible heat flux, this fact presented a big challenge to the evaluation of the modelling results, which, however, could not be solved in this thesis. Independent from the energy balance closure, the simulated latent heat was still overestimated in August. Also the simulated net ecosytem exchange showed a differring mean in this month as a result of an overestimation of the carbon respiration. Thus, the impact of the special climatic conditions in 2003 on the net ecosystem exchange and the latent heat flux modelling at the FLUXNET station Waldstein-Weidenbrunnen could be demonstrated. On the one hand, the results of this thesis could interest ACASA model users and on the other hand provide a basis for an improvement of the model parametrization for the investigation site. However, in the course of the interpretation of the results it was shown that, for some modules in ACASA, improvements are necessary.

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Weather research site ÖBG
Luftdruck (356m): 980.6 hPa
Lufttemperatur: 1.1 °C
Niederschlag: 0.0 mm/24h
Sonnenschein: <1 h/d
Wind (Höhe 17m): 6.0 km/h
Wind (Max.): 12.6 km/h
Windrichtung: SO

last modified 2010-07-25