In July 2021, Germany experienced its largest and deadliest flood disaster in the past 60 years when heavy rainfall caused a catastrophe in Ahr Valley and surrounding areas. In some locations up to 200 litres of rain per square metre fell within hours, causing rivers to rise to levels more than twice the historical records. The Ahr River and other rivers burst their banks, destroying entire towns and villages. More than 180 people lost their lives 10,000 buildings were damaged or destroyed, and the damage value was estimated at NZ$30 billion (€15 billion).
The event revealed serious weaknesses in early warning systems, emergency coordination, and infrastructure resilience.
Events like this show how vulnerable even well-developed systems can be. Drinking water supply, wastewater treatment, stormwater networks, and pump stations are at risk. Pipes can be damaged by ground movement and treatment plants can be temporarily forced to shut down because of flooding or power loss. Aotearoa New Zealand faced similar devastation in February 2023 during Cyclone Gabrielle, which is described as the country's most costly non-earthquake disaster. The storm caused an estimated NZ$14 billion in damage, with Hawke's Bay and the Gisborne region among the worst affected.
In Esk Valley, floodwaters rose so rapidly that homes were submerged within hours. Across the country, 225,000 homes lost power, critical infrastructure was damaged, and entire communities were cut off for days.
These bigger events make the headlines. However smaller, more frequent events are also putting pressure on water systems. Short, heavy rainfalls overwhelm stormwater networks, leading to sewage overflows into rivers, harbours, and coastal areas.
©Water New Zealand