Despite a relatively low distribution of the rain sensors in the region, the combined analysis of all rain sensors showed promising results. As the rain started around 20:37, the rainfall intensity gradually increased and eventually led to the ›Violent‹ rain event. The rainfall intensity with extremely heavy rain lasted about 30 minutes from 20:48 to 21:16. The maximum rainfall event lasted around 17 minutes. This storm reportedly spread throughout the region, causing flooding and massive disruption to the city and the public transportation.

The hydrograph of the four water level sensors displays the sudden rise in the river immediately after the heavy rain event (fig.2). Within 30 minutes of the start of the intensive rain, the water level at the downstream station of Liederbach Town Hall Rathaus rose from 0.089 m to 1.557 m (almost 1600 % increase). Located upstream, the Alt Niederhofheim bridge was flooded and obstructed by the massive wood debris as well as another station in the neighoring Kelkheim. The water level peaks there were seen as early as 21:10 when the violent rainfall had lasted for around 15 minutes. More rainfall events in the upstream region could have influenced this rise in water levels and the peak values.

If distributed over several catchment areas on a large scale, the rainfall sensor network can capture the realtime rainfall data. Those in combination with public weather information and a dedicated AI lead to a highquality heavy rain forecast. The sensitive and vulnerable zones could be defined as the focus of the early warning system, giving the responsible authorities and emergency services sufficient time to prepare for such extreme rainfall events up to 60 minutes before the actual rain event. From this event in Liederbach, the massive flooding was observed about 30 minutes after the start of the rain event in the affected catchment area.

NIVUS RAIN is provided to users as a digital service, built on a sensor and cloud network maintained by NIVUS and its operators. In spite of the advances in non-contact water level monitoring, there is always a possibility that the sensors installed on the ground will be flooded or hindered by debris, as observed at Alt Niederhofheim and Liederbach Town Hall. In such cases in the future, a flood would have caused massive destruction, by the time the water level sensors are back in operation. The RMI rainfall sensors, on the other hand, are not only maintenance-free but also strategically distributed in dense swarms and installed above the ground. This design provides a significant advantage over traditional measurement systems, ensuring the detection of even the most catastrophic events without any oversight.