How much Canterbury flood damage was caused by climate change
Within a few weeks, scientists will have estimated how much climate change contributed to last weeks Canterbury storm and floods. Its called attribution science and New Zealand researchers have been working on it since 2009, Niwas principal climate scientist, Dr Sam Dean, says. The problem has been that getting an answer has taken many months, by which time people have moved on, he says. But two pieces of work are under way that may produce answers within days after an extreme weather event. Attribution has a really strong role in communicating with people the idea that climate change is the here and now. It's not something for the distant future, Dean says. READ MORE: * Canterbury floods: Is climate change to blame for severe weather events? * Critical need for accurate forecasting, climate experts visiting Wellington say * Climate change was behind 15 weather disasters in 2017 * Niwa urges farmers to prepare for climate change * Scientists just linked another record-breaking weather event to climate change I spent years talking about what might happen in the year 2100 if we don't mitigate climate change and that's still true, but it disengages with people. It's much more powerful to [show that we] live in a different world now. We've already had more than a degree of warming and that is affecting everything from ecosystems to floods to heat waves to droughts. Both research programmes work from the same premise that you can create models of what a weather event would have been like if anthropogenic greenhouse gases were not elevated. They call it a counterfactual and its hypothetical thats based in part on New Zealand weather data collected over decades. Then you compare the counterfactual to what actually happened in, for example, the Canterbury storm and floods , and calculate the difference. Using earlier models, Dean and others analysed a storm and floods that hit Northland in 2014. It was much like the Canterbury event an atmospheric river was parked over the region for five days and extreme levels of rain fell, causing floods. The researchers compared the observed data with several models of previous weather and found the fraction of the risk of the event that is attributable to anthropogenic climate change was 47 per cent, or almost half. This was published in 2015 and the authors had medium confidence in their results. Since then, MBIE has funded the Extreme Weather Event Real-time Attribution Machine a three-year, year, $1 million research programme that could produce estimates within days, says Dr Greg Bodeker of Bodeker Scientific, a consultancy heading up this piece of work. While massive advances have been made in attribution science in the last decade, it remains a challenging problem, requiring careful and considered analyses of several lines of evidence to be confident in any attribution statement, he says. Meanwhile, Whakahura: Extreme Events and the Emergence of Climate Change a five-year, $10m programme is contributing to the attribution science while also looking at the wider picture of attribution, including the economic costs of climate change, and looking into future events. Theres lots of crossover between these projects, which involve scientists from Niwa, MetService, Canterbury, Victoria and Oxford universities and elsewhere. For years, scientists have been saying that as the climate warms, the atmosphere is capable of holding more water and therefore rain can be harder, Bodeker says. But that says nothing about how the intensity or frequency of a specific event would have been different in a world devoid of anthropogenic greenhouse emissions. If the models can be validated, thats about to change and New Zealanders will get regular estimates of how much climate change contributed to extreme weather events.