Open Access

Mohsen Soltani

• In the TERrestrial ENvironmental Observatories (TERENO) prealpine region, the temporal and spatial variability of water and energy fluxes is highly influenced by the heterogeneity of land-surface characteristics. In this region, ecohydrometeorological variables and processes like soil moisture, evapotranspiration (ET), vegetation type and dynamics, and surface heat fluxes exhibit rapid changes within short distances. This is mainly due to the heterogeneity in topography, soil-landuse properties, and land-surface interactions. The energy –and water budgets in such environments are thus highly controlled by the domain characteristics. Therefore, accurate spatial variability of the hydrometeorological variables can be only achieved with a distributed physically-based high resolution hydrologic modelling approach. Such models take into account all domain characteristics by simultaneously solving the water and energy balance over complex mountain terrain. This PhD thesis investigates: i)In the TERrestrial ENvironmental Observatories (TERENO) prealpine region, the temporal and spatial variability of water and energy fluxes is highly influenced by the heterogeneity of land-surface characteristics. In this region, ecohydrometeorological variables and processes like soil moisture, evapotranspiration (ET), vegetation type and dynamics, and surface heat fluxes exhibit rapid changes within short distances. This is mainly due to the heterogeneity in topography, soil-landuse properties, and land-surface interactions. The energy –and water budgets in such environments are thus highly controlled by the domain characteristics. Therefore, accurate spatial variability of the hydrometeorological variables can be only achieved with a distributed physically-based high resolution hydrologic modelling approach. Such models take into account all domain characteristics by simultaneously solving the water and energy balance over complex mountain terrain. This PhD thesis investigates: i) the turbulent flux variability and energy balance closure, ii) the spatiotemporal variability and dependence structure of the coupled water –and energy fluxes (via forward modeling), iii) and the sensitivity and uncertainty pertaining to hydrological model parameters (via inverse modeling) in the TERENO prealpine region, southern Germany. This is achieved by i) using the Eddy Covariance technique (EC), ii) application of the distributed hydrological model GEOtop and empirical Copulas, iii) and a combination of GEOtop and the Parameter ESTimation tool (PEST) for this complex region. To obtain the above research objectives as best as possible, this thesis is structured and organized into three main- result parts as follows: In the first part, the turbulent flux variability and energy balance closure (EBC) is characterized for the TERENO EC sites during 2013-2014. The main goals are to characterize the multiscale variations and derivers of the turbulent fluxes, as well as to quantify the EBC. The results show significant differences in the mean diurnal variations of the turbulent fluxes. The radiation (29.5%) and temperature (41.3%) components are found as the main drivers of turbulent fluxes. A general lack of EBC is observed. On average, 80% of the flux footprint is emitted from a radius of 250 m around the EC stations. In the second part, the spatiotemporal variability and dependence structure patterns of the coupled water and energy fluxes are quantified using the GEOtop model and empirical Copulas for the Rott (~55 km2) and Upper-Ammer (~300 km2) catchments in the TERENO prealpine region over two summer episodes in 2013 and 2015. GEOtop is capable of quantifying the temporal and spatial variability of the water and energy budgets with consideration for elevation-gradient effect of this heterogeneous landscape, which is confirmed by the linear statistical metrics applied for the model performance evaluation. Furthermore, the empirical Copula-based dependence structures of the measured and simulated hydrometeorological variables indicate that the highest densities are found in the lower and upper ranks. This suggests a reasonable performance of the model for the low and high values, which, the model has poorer performance in the middle ranks of the data. In the third part, an inverse modeling of the streamflow and turbulent fluxes together with the associated parameter sensitivity and uncertainty analysis is performed using the developed GEOtop-PEST interface in the Rott catchment over two summer episodes in 2013 and 2015. Using this interface, the value added by including turbulent flux data in the parameter estimation process is particularly investigated, and the impact of the additional flux data on the uncertainty bounds is analyzed. A set of model parameters that allowed reproducing both observed streamflow and turbulent heat fluxes were identified. The majority of the estimated parameters were highly sensitive to the considered variables. It was found that the confidence bounds of estimated parameters are narrowed significantly when considering not only streamflow observations, but additionally turbulent flux measurements in the calibration process. Also, correlations between estimated parameters could be reduced. The results presented in this thesis contribute to further improve our understanding of the hydrometeorological impacts, land-atmosphere interactions and the hydrological cycle in time and space over the TERENO prealpine region.…