Rainfall partitioning respond for a wet and dry year conditions

The climate change strongly influences the hydrological cycle mainly due to redistribution of precipitation and changes in its seasonal patterns, resulting in longer dry periods and more intense heavy rainfall events. As precipitation is the main input for rainfall interception, throughfall and stemflow, we can expect the climate change to influence also these processes. In our study plot in Ljubljana, Slovenia, covering a small urban park with two separate groups of trees (Pinus nigra Arnold and Betula pendula Roth.), we have been performing throughfall, stemflow and rainfall measurements since January 2014. In that period, we have captured various rainfall events and the measurements are available for different periods. Among them we have also covered an especially wet (2014) and a dry (2015) year. According to the long term yearly rainfall amount, equal to 1355 mm, the total rainfall amount delivered during the year 2014 was much higher (1841 mm) and in the year 2015 considerably lower (1106 mm), which characterize those years as a wet and a dry one. For each year we have analysed the influence of meteorological conditions (e.g. rainfall amount, duration, intensity, air temperature, vapour pressure deficit, size and velocity of raindrops) on rainfall interception, throughfall and stemflow under each tree species using the boosted regression trees and random forest approach. Similar influences of the variables were recognized by both models. Comparison of the obtained results with previous analysis (e.g. Zabret et al., 2018, doi: 10.1016/j.jhydrol.2018.01.025; Zabret and Šraj, 2021, doi: 10.3389/ffgc.2021.663100) showed that the indicated influential variables for wet and dry year are to some extent similar to the variables, indicated as influential in leafless and leafed period. For example, the rainfall duration was recognized as one of the most influencing variables on rainfall interception during the wet year 2014, which was previously observed also for the leafless period. Additionally, rainfall intensity had significant influence on rainfall partitioning by birch tree during the dryer year 2015 as well as in the leafed period.