Rainfall Interception by Urban Trees and Their Impact on Potential Surface Runoff

Urbanization changes the natural environment, alters land use, and affects the hydrological cycle. Due to decreased infiltration, runoff appears faster with higher flow peaks. A nature‐based solution is to plant trees because they intercept precipitation and help to reduce water reaching the ground, forming surface runoff. Rainfall partitioning for birch ( Betula pendula Roth.) and pine ( Pinus nigra Arnold) trees is measured in the city of Ljubljana, Slovenia, during 2014 and 2015. The measured values for two consecutive years are used to estimate potential surface runoff reduction due to planting of the trees at a parking lot. The results demonstrate that birch and pine trees intercepted 23 and 45% of gross rainfall, respectively. Both tree species intercept more rainfall in the leafed period. Additionally, rainfall interception during wet (2014) and dry (2015) years has been compared. In 2014 rainfall interception is highly influenced by rainfall intensity, while it has a negligible impact on rainfall interception in 2015, when air temperature is more influential. The scenario of covering 10% of the parking lot area with the trees results in runoff reduction of up to 7.3% per year. In general, runoff reduction is higher in a wet rather than a dry year. The new findings about the performance of different tree species in different climate conditions can offer valuable information for the decision makers and landscape designers about the benefits of trees in urban areas.