Canterbury floods: Is climate change to blame for severe weather events?
Climate change modelling suggests we will see more frequent and more severe weather events. As Canterbury recovers from another flood , reporter JOANNE NAISH asks whether climate change is to blame. Many Cantabrians forced to flee their homes amid a deluge of rain all said the same thing: they had never seen rivers rise this high, or this fast before. With the world facing inevitable climate change, scientists say heat waves, droughts, storms, wildfires, and warming oceans will get progressively worse. Victoria University climate change expert James Renwick says it is too early to say whether the Canterbury floods this week were caused by climate change, but the event is exactly what we can expect more of as the earth heats up. READ MORE: * New climate change targets put future of West Coast coal mines in limbo * 'Atmospheric rivers' drive New Zealand's wet and extreme weather * Scientists' estimate of rising costs of climate change could improve planning The Intergovernmental Panel on Climate Change describes the effects of a 1.5 degree Celsius increase in a special report released last year. It will cause average temperatures across much of the world to increase, while several regions will get much wetter, and others will experience drought. Limiting warming to 1.5C will require cutting global emissions by 7.6 per cent every year this decade. The average global temperature is currently about 1.2C higher than it was at the time of the Industrial Revolution, some 250 years ago. We are already witnessing localised impacts, including widespread coral bleaching on Australia's Great Barrier Reef. Canterburys extreme rain event this week led to a regional state of emergency and hundreds of evacuations, including the entire town of Springfield. Ten state highways and 52 schools were closed at the storms peak. Farmers fled for their lives, with some describing heart breaking scenes of lost stock and a wall of water that caused significant damage to their properties. Officials have urged people to stay home and keep off the roads until the flooding recedes, but they should head for higher ground immediately if they see rising water. Renwick says the event is something we are likely to see more of. Climate change doesnt cause it, but it does make it worse. Its a bit early to say whether it is a one-in-100-year or 500-year event, or what the role of climate change has been. But one thing is for certain: as it gets warmer the air will hold more moisture and the more wet weather there will be. Renwick says it will be very surprising if there isnt climate change significance to what happened in Canterbury given the speed with which rivers rose and the amount of rain that fell. Some areas in Canterbury usually see only 50mm a year but they got up to 300mm in a day. Thats exactly what we expect with climate change: its drier when its dry and its wetter when its wetter. The good news is that if we cut emissions now, the predicted increase in severe weather events will not happen. Glaciers and ice caps will continue to melt even if we drastically reduce emissions now, because they take many years to respond to climate change. But the increase in extreme weather events and storms will stop pretty quickly, Renwick says. University of Auckland Faculty of Engineering associate professor Asaad Shamseldin says the extreme rainfall and flooding in Canterbury appears to be linked to an atmospheric river . Atmospheric rivers are large, flowing amounts of vapour water. They are a major contributor to the water cycle, leading to severe floods, broken droughts, and more strong winds worldwide. There is very limited understanding about the impacts of atmospheric rivers in New Zealand. However, our recent published research showed that these atmospheric rivers are linked to extreme rainfall in New Zealand, he says. The research authored by Shamseldin, Jingziang Shu and Evan Weller found droughts and floods are the most costly and damaging natural hazards in New Zealand. Under the changing climate, the frequency and magnitude of floods are likely to increase as a result of the increased frequency and intensity of extreme rainfall, the research says. Climate change is expected to also lead to increases in the frequency of droughts in vast areas of the North Island, including regions where atmospheric rivers are the major contributor to water resources. Climate change will result in between 20 and 60 per cent more frequent and stronger atmospheric rivers. Shamseldin says Canterbury communities will not only face significant disruption to daily life, but also serious health risks due to water being contaminated with wastewater. Given extreme weather events are expected to become more frequent, decision makers and communities need to figure out ways to adapt and mitigate the risks, he says.