The Insurance Council of New Zealand has welcomed calls from the country’s peak climate change body to overhaul stormwater and wastewater systems to cope with extreme weather.

Deep South says most of the 24,000km public wastewater network, 3000-plus pumping stations and 17,000km stormwater network is not designed for sea level rise, nor predicted changes in rainfall levels and frequency.

The recent Edgecumbe floods highlighted the problem, with raw sewage in streets and homes uninhabitable six months after the event.

Insurance Council CEO Tim Grafton says most underground infrastructure was built before knowledge of climate change, and before urban areas were densely populated.

“More frequent and extreme weather events will mean stormwater drains will not cope, causing flooding, and the cascading impacts of sewerage contamination and damage to other infrastructure,” he said.

Deep South researcher Iain White says it is expected climate change will adversely affect stormwater and wastewater systems, valued at more than $NZ20 billion ($17.87 billion), affecting health, disaster resilience, drinking water, ecology and communities.

“For example, in many local water systems, roads are designed to be used as secondary stormwater routes in extreme flooding,” he said. “This is fine in most situations, but in extreme inundation events wastewater containing sewage may mix with the stormwater overflows, which, of course, brings problems such as we saw in Edgecumbe.”

Deep South says drought can disrupt gravity systems by slowing flows and leading to blocked pipes, and can affect wastewater treatment processes, creating functional and safety concerns.

Mr Grafton has welcomed the new Labour-led Government’s focus on adapting to climate change, which includes a long-term action plan similar to that of the UK.