Ruchika Perera1, Brendan Cullen1, Richard Eckard1
1 Faculty of Veterinary and Agricultural Science, University of Melbourne, Melbourne, Victoria, 3010, email@example.com
Most studies of climate change impacts on pasture systems have focussed on pasture growth responses to average changes in temperature and rainfall but, the impacts of increased frequency and severity of extreme climate events (droughts, floods and heatwaves), may be more harmful than changes in average climate. To test the impact of extreme climate events on pasture yields, prediction equations using mean annual and seasonal rainfall and temperatures were compared to ones that also incorporated extreme events (including ‘wet’ and ‘dry’ periods based on the standardised precipitation index, frost days, frost duration, hot days and hot day duration). Pasture growth was simulated with DairyMod using daily climate data (including historical carbon dioxide (CO2) concentrations) from Ellinbank and Dookie sites in south-eastern Australia for the period 1960-2015. The regression equation with mean climate statistics at Ellinbank and Dookie explained 52.3% and 71.2% (R2) of the annual yield variation respectively. The regression equations that also incorporated extreme events explained 62% and 89% of the yield variation at Ellinbank and Dookie respectively with annual rainfall, winter temperature and CO2 being the favourable climate factors. However, extremes of rainfall distribution (wet and dry months) and the hot day (>30°C) duration affected pasture growth negatively. Analysis of climate records at Ellinbank showed that spring maximum temperatures and the hot day duration had increased in recent decades demonstrating the importance of extreme climate events in the variability of pasture-based systems and highlighting that they must be considered in future pasture growth studies and climate change analysis.