Influence of age, soil volume, and climate change on water availability at urban tree sites

Conditions for trees are challenging in urban areas with a high degree of soil sealing combined with changing climatic conditions. Stress is a primary mortality factor, especially for young trees that do not yet provide ecosystem services such as sufficient cooling. Therefore, sustainable tree planting in an urban environment must create conditions so a tree can grow into a large tree and be preserved for a long time. We developed a daily water balance model of urban trees in a temperate climate, focusing on realistic planning scenarios for five locations in Germany for current and future climate conditions. The aim was to understand annual and seasonal variation in soil water content (SWC) and the drought stress intensity. We modeled the SWC for trees ages 10 to 60, a crucial parameter for analyzing site conditions, and quantified drought duration and correlation to extreme heat. The results show that age strongly impacts drought duration. Imperviousness and root volume have a higher impact on drought intensity than future climate change. We conclude that it is crucial to consider sealing and root space when planning urban tree locations to preserve vital trees in the future.