Rainfall interception - Localization of water storage and evapotranspiration in forests

• Applicant: Professor Dr. Christian Bernhofer
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Atmospheric Science
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 324915082

Interception of precipitation has a significant influence on the availability of water in ecosystems. Especially in forest ecosystems evaporates up to 50 % of precipitation via interception which is not available to plants. The process is highly variable and is not yet described by models satisfactorily. Statistical methods for the determination of model parameters, and conceptual approaches describing the processes incompletely, produce significant uncertainty in the quantification of interception. In particular the statistical parameterization and the weak consideration of the structure and properties of vegetation stands prevent the transfer of experimental findings to other sites. However, this is mandatory to account for effects of changing rainfall patterns and land use on the future water budget.The aim of the proposed project is the considerable reduction of uncertainties in interception assessment and modelling by investigation and parameterization of the small spatial variability of the process. It is known that rain events with low intensity are intercepted by the outer layers of forest stands which are characterized by strong atmospheric coupling and effective evaporation. In comparison, rain events with high intensity exceed the storage capacity and also produce wet layers, which dry very slowly. This nonlinear behavior is still not sufficiently included in interception models due to a limited consideration of the vegetation structure. In the project, the mechanisms of water storage and interception within the canopy shall be examined on the basis of detailed measurements (micrometeorological, hydrological and via laser scanning), and new approaches will be developed and tested which parameterize the dependencies with regard to vegetation structure. Standard interception estimates of forests are based on throughfall collected through spatially distributed precipitation gauges or large troughs and on model results without taking the three-dimensional spatial heterogeneity of the stands into account adequately. The resulting error in the parameters and model outcome has not been investigated and quantified yet. The new modeling approach with high spatiotemporal resolution will allow the assignment of the simulation results to individual throughfall collectors, as well as the comparison with micrometeorological measurements of evapotranspiration. The required detailed vegetation model is provided from terrestrial laser scanning. Therefore, the simulation of the interception process will be conducted with a spatial-temporal resolution of 1 m³ and 1 min in a range of 600 m × 600 m around a well suited Fluxnet tower, which provides a unique set of almost 20 years of micrometeorological and hydrological measurements. By this combination of experiments and modelling it is expected to generate a step-change in understanding of interception.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Ronald Queck