Sustainable irrigation system for thirsty trees

The consequences of climate change are making themselves felt in many places: Not only are there more and more pronounced periods of heat, but also more and more extreme weather events. Cities are becoming heat islands and sometimes heat up so much that it can be ten degrees hotter than in the surrounding area. On the one hand, this means that urban trees often have to be watered in summer at great expense. On the other hand, heavy rainfall events put a strain on the urban area: due to the many buildings and the high proportion of sealed surfaces, flooding occurs quickly. How can urban trees be watered more intelligently during hot spells and how can rainwater be stored at the same time to avoid flooding?

Together with Prof. Dr.-Ing. Helmut Grüning from Münster University of Applied Sciences, Humberg GmbH is developing underground rainwater storage tanks in the root zone of trees in the BeGrüKlim project. These are filled via the existing drainage system, for example with rainwater run-off from car parks or the roofs of adjacent houses. If it then becomes very hot and dry, the trees are efficiently watered via the systems.

For this purpose, sensors monitor the fill level of the retention tanks and the moisture level of the substrate. The data can be sent wirelessly via the mobile phone network to the responsible department of the city administration, so that employees can specifically refill empty "tanks" under trees if it has not rained for a long time. On the other hand, during heavy rainfall, the water can first fill up the underground tank before it flows into the sewage system. This relieves the burden on the sewage system. In addition, the trees reduce the heat island effect in the cities through their transpiration.

The BMU-funded BeGrüKlim project started at the beginning of 2020 and will run for three years. During this time, trees will be planted with the innovative planting pit systems at three locations in the municipality of Nottuln. This waters the trees as needed and reports dry conditions by sensor. In addition, trees without rainwater storage were planted so that it can be compared whether those with storage come through dry periods better.

The project is also investigating how the system dimensions can be optimised, to what extent it can be connected to the drainage systems and how the cost-benefit ratio will develop. The Humberg company has already planted trees with reservoirs on its own premises to test the system further.