Understanding the impacts of climate change on lamb survival and lambing date in Southern New Zealand

Future variations in temperature, rainfall and storm intensity need to be translated into on-farm metrics to understand the impacts on lambing date and survival. A lamb survival model based on heat loss was developed and applied in a daily time step to present and future climate scenarios, at three regions throughout the lower South Island representing hill and lowland farms. Future scenarios (2040-2049) were modelled, based on forecast climate trends. Changes in temperatures from the 1990-1999 period to the 2000-2010 period matched or exceeded change predictions from global modelling. Predicted increases in temperature had little effect on lamb survival. Average air temperature over the period two weeks before to four weeks after planned start of lambing was ~7ºC in every region and topography, matching the rise in spring pasture growth. Future climate scenarios indicated the potential to schedule lambing 10 to 20 d earlier than current practice by 2040, hence increases in lamb liveweight of 1.5 to 5.5 kg by December 15th may be possible. Opportunities to lamb earlier as increased temperatures promote earlier grass growth in spring may help increase pre-summer lamb liveweight gain and mitigate the potential impacts of increased occurrence of summer dry periods.