Challenge / Goal
Essen's more than 200,000 trees are in a bad way in hot summers. Nowadays, every fourth tree suffers from drought stress and has to be watered intensively to prevent it from dying. In the past ten years, the city has lost around 34,000 trees in the city. At the same time, however, these are becoming increasingly important in times of climate change.
With the help of Copernicus satellite data on drought stress, coupled with soil moisture sensors, the actual watering requirements can be determined. In a first pilot phase, 45 selected urban trees, as well as trees that are particularly worthy of protection as tree monuments, were equipped with sensors (now already 80 are equipped). The smart technology is "hidden" underground and high above our heads: The soil moisture sensors are placed in the root area of the trees. The area-wide LoRaWAN data network of Stadtwerke Essen is primarily used to transmit the information. The sensor data are transmitted wirelessly to databases where they are evaluated by the city foresters and provide information about the condition of the soil. By enriching the satellite data with these sensor measurements, city-wide monitoring is implemented.
The researchers at the University of Trier use images from the European satellite programme "Copernicus". Every three days, a satellite traverses the city area and acquires imagery in pixels of ten times ten metres grid size. By analysisng the acquired data, information about the chlorophyll content of the leaves and thus about the health of the trees, can be obtained. Since the spectral signature of the tree crown surface changes depending on their water supply, the satellite images can be used to identify the effects of drought stress for large urban trees individual tree reference. To avoid drought stress, reliable data on the current soil water supply and their weather-dependent development are needed at an early stage to complement the water supply management for urban trees.
The sensors utilised at tree root level are so-called suction tension measuring devices, which measure the force required in a ceramic body for the necessary negative pressure which the root must generate in order to be able to extract water adhering to the soil and absorb it with the appropriate nutrient solution. On each city tree, three such sensors measure this suction force at depths of 30, 60 and 100 centimetres below the surface. The sensors are connected by cable to a central unit for power supply and measurement data communication, which in turn transmits the measurement data wireless to the municipal data processing centre in the Essen system house using the Stadtwerke Essen's LoRaWAN radio data network.
Geoinformatics experts evaluate the measurement data with the help of special software and compare it with satellite images for interpretation. Based on the data interpretation, reliable statements on water supply for the bulk of city trees not equipped with sensors are expected.
Want to learn more about the lessons learned, financial details and results?