West Coast rivers early sentinels of climate change
Rivers on the West Coast will likely give early and clear signals that climate change is upon New Zealand, a new study has found. This will probably start happening after 2050. Rivers on the east side of the South Island will also give early signals, especially those that rise in the Southern Alps, the study by hydrologist Dr Daniel Collins found. Rivers elsewhere in the South Island and on the North Island will be less noteworthy as climate change sentinels. Some rivers will show few or no effects from climate change, the model predicted. Collins study looked at river flows, not floods or coastal storm surges. He also didnt look at biological effects of climate change in New Zealand rivers. READ MORE: * New technology will change the way farming is managed in the future * Climate change: Are Australia's wildfires New Zealand's future? * Third controversial Mid-Canterbury irrigation consent approved * Farmers volunteer to start water rostering in Otago as rivers reach low levels * Southern Alps will likely save NZ from 'river piracy', but they won't save our retreating glaciers Higher river flows are predicted for the West Coast and South Island rivers because increased precipitation is predicted to fall on the Southern Alps as a result of climate change. This is particularly the case in winter. Meanwhile, higher air temperatures will have a disproportionate effect on river flow in snow-affected alpine areas. Indeed, runoff is predicted to shift from winter to spring. All that water will flow to the West Coast and into rivers such as the Clutha River/Mata-Au, Rakaia and Waimakariri that rise in the Alps and flow east and south. Mean winter flows [are] the most extensive sentinel of climate change in New Zealand rivers, Collins wrote in the Hydrological Sciences Journal recently. His model looked at river flows in spring, summer, autumn, and winter, as well as mean annual flows and low flows, to identify which of are projected to emerge first and most extensively. Scientists and governments have been much concerned by the time of emergence of climate change the point when a climate change signal becomes distinguishable from background effects. Its devilishly difficult to do. Its like eavesdropping on a conversation in a noisy bar, Collins said in an interview. Depending on the variety of factors, the time of emergence could be soon, late century and not this century. Faced with this uncertainty, Collins went looking for the order of emergence which hydrological metric is likely to emerge first and where. This reduced uncertainty around timing and told decision makers what to look for. Some things in nature will show the fingerprints of climate change earlier than others, and we should pay attention, he said. He found very little emergence occurs by mid-century for any metric, and in some instances no substantial emergence occurs during the entire simulation period, which ended in 2099. But higher river flows on the South Island start turning up sometime after 2050. Decision makers need to be thinking about higher waters now because infrastructure built or improved now will last many decades, he said. Road bridges in the affected areas were an obvious concern. Collins also singled out irrigation schemes. Those in Canterbury and Otago may have more water available to them, but it may come earlier in the year and more storage may be needed. Similar scenarios face hydro-electricity generators. More water in winter. He did not find that mean winter river flow was the only early or best sentinel of climate change. Sea-level rise and glacier retreat were also sentinels. We should watch these things, he said. Collins did most of his modelling while at Niwa. Hes now at Lincoln University studying environmental policy and management.