An environmental think-tank is warning farmers that a mega El Nino could be on the way, bringing with it severe droughts.
The Australian Bureau of Meteorology said a substantial El Nino event has begun, but New Zealand forecasters said they did not believe there was enough evidence yet to make that call.
A former Fonterra manager and now the chief executive of the think-tank Nouveau Eco, Belinda Storey, said the last mega El Nino was in 1998 and the world was due for another.
Ms Storey said New Zealand dairy farmers were now more reliant on imported feed, particularly palm kernel expeller from Malaysia and Indonesia, than they were in 1998.
And she said this made them more vulnerable.
"New Zealand stocking rates are much higher than they were the last time we expected a mega El Nino, and we're much more dependent on imported feed than we were previously.
"Most farmers don't recognise that El Nino doesn't just impact Australia and New Zealand. It also has a very dramatic impact in Indonesia and Malaysia," she said.
"(We need to) connect those dots between an El Nino impact in New Zealand and our dependence on imported feed from countries that are likely to experience a severe drought, themselves."
Ms Storey said climate change meant the world was warmer now that it was in the 1990s, and said the higher temperature base could mean an unprecedented El Nino could develop.
"The level of drought that could be experienced in New Zealand and Australia could be greater than we've experienced in any previous mega El Nino.
"We haven't been in that situation and we haven't had the current stocking levels, so if farmers don't undertake measures to reduce stocking levels, once they have a clear idea that a mega El Nino is coming, as they go into summer and autumn, it's very likely that they won't have the food on New Zealand farms to feed them."