The rainfall falling above the vegetation is divided into intercepted rainfall not reaching the ground and into throughfall and stemflow reaching the ground in different ways. The share of each rainfall interception component depends on meteorological variables describing properties of rainfall events and vegetation variables giving the properties of the tree. Knowing and understanding the influences of those variables is important for estimation of the rainfall interception process and its influence on other natural processes such as surface runoff reduction, increase of rainfall erosivity, reduction of soil erosion, enrichment of ground water, and nutrient cycle. Throughfall and stemflow were measured in a small park in Ljubljana between 1 January 2014 and 30 June 2017 under the common silver birch (Betula pendula Roth.) and Austrian pine (Pinus nigra Arnold) trees. In the same period meteorological and vegetation variables were also measured.
In the first part of this dissertation, we described the process of rainfall interception, the changes of throughfall across space and time, and the influence of rainfall interception on surface runoff reduction. Meteorological and vegetation variables were presented in detail and their consideration in other studies was stated. The study plot where the measurements were taken was also described, and the measurement and data analysis techniques were presented.
In the second part of the dissertation, the results of precipitation in the open, throughfall and stemflow were presented, the estimated values of rainfall interception were given, and the measured values of meteorological and vegetation variables were listed. We also estimated the influence of the trees on surface runoff reduction in the urban area. The influence of the variables on the components of rainfall interception was analysed for spatial distribution of throughfall under the canopies, for temporal variability of throughfall with the development of the event, and for the average values of the variables per events.
We have shown that meteorological and vegetation influences interact closely. According to phenoseasons, the most influential meteorological variables were the amount of precipitation in the vegetation period and the rainfall intensity in the dormant period. This depends also on the leaf area index, canopy storage capacity, water bark storage capacity, and branch position. These variables also induced the changes in the spatial pattern of throughfall under the birch tree's canopy in the phenoseasons. Additionally, the rainfall microstructure also significantly affected rainfall partitioning. Larger and faster raindrops initially increased throughfall in the case of the pine tree, and induced the start of throughfall under both tree species.