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It seems that ‘once in a hundred years’ rainfall is becoming more like ‘once a month’ as a result of climate change

Editorial April / May 2017

The Tasman Tempest, Cyclone Debbie, tropical torrents – call them what you will, but they have all delivered record-breaking rainfall figures during March and April, putting our stormwater infrastructure under immense strain.

The Tasman Tempest – the deep low that formed in the Tasman Sea in mid-March – delivered unprecedented levels of rainfall and widespread flooding to the North Island. NIWA meteorologist Ben Noll – who coined the name for the storm – says more rain than typically falls for the whole of March fell in a period of just a few days, with instances of ‘once in a hundred years’ rain and several areas experiencing their ‘wettest hour’ on record.

Then in early April, the remnants of Cyclone Debbie produced up to three times the normal monthly rainfall for some locations in just three days, bringing more misery to urban and rural locations still in mop-up mode after the previous drenching. The residents of Edgecumbe – a Bay of Plenty town with a history of flooding – were evacuated when the Rangitaiki River breached its flood bank, flowing into the township and leaving many streets underwater.

Now, as I write this editorial, the rain is once again hammering on our office roof and the road outside is awash. It seems that ‘once in a hundred years’ rainfall is becoming more like ‘once a month’ as a result of climate change. “While no one weather event is caused by climate change, all events are influenced by climate change since the atmosphere is now warmer and moister than it was in the past, which increases the likelihood of extreme rainfall,” says Ben Noll, all of which leaves local and regional councils struggling to cope with stormwater management.

Perhaps the answer may come from China’s ‘sponge cities’ programme. Funded by central and local government and the private sector, the programme involves a number of pilot cities in which an integrated urban water system is built that provides solutions for excessive runoff that utilise natural retention, infiltration and purification as far as possible – just like a sponge. Instead of water-resistant concrete, permeable materials and green spaces are used to soak up rainfall, and rivers and streams are interconnected so that water can flow away from flooded areas.

It’s certainly an ambitious project involving water governance, financing structures and technical measures, but the results will be worth considering by our own water managers.

Until next time …
Lynne Richardson, editor


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