WA growers will have to become the most efficient in the world to manage a new climate emerging across the country. Data analysed by the Australian Grains Export Innovation Centre (AEGIC) reveals traditional rainfall zones have changed significantly since 2000 and growers should plan their seasons based on the past 15 years. AEGIC agro-meteorologist David Stephens revealed his findings at the Grains Research and Development Corporation (GRDC) Grains Research Update in Perth this week. From analysing more than 8000 Bureau of Meteorology stations around the country he has seen a shift in WA's rainfall from winter to summer, with 50 millimetres of winter rain lost and 25mm of summer rain gained on average. "The increasing summer rain means they've got to utilise that out of season rainfall more and more," Dr Stephens said. "The spraying of summer weeds and early sowing really becomes important. "Also, all the work on trying to improve water storage on properties and nutrient efficiency with soil amelioration combined with all the zero till and new technology means that growers are really going to have to be focused on water use efficiency." Dr Stephens said the traditional mid-year rain in June and July had decreased and this was particularly evident in 2015. "We used to have truncated rain fall in June and July and that's where the rainfall has really dropped off," he said. "That's the classic time when the Indian Ocean trough formed out to the west of us and that's what weakened dramatically in the mid 1970s and then in more recent decade as well. "Last year we had some of the weakest upper level low pressures over the Wheatbelt and out to the west of WA ever recorded. "It was lining up with a very balmy, sunny winter where we had hardly any cold fronts of significance." Dr Stephens said a cut off low over the Indian Ocean "saved our bacon" last year but it was becoming more normal for this to occur instead of the classic cold front bands which have always been the regular winter water suppliers. He said while growers traditionally had their seasons mapped on past experience, they should be mindful of considering only the past 15 years based on his findings. In this time there had been a general increase in summer rainfall across the entire county, a decrease in winter rainfall and an obvious change to growing seasons. Dr Stephens said the Merredin CBH grain bin opening date had moved forward six weeks since 1970 while the net growing season for that area had shortened by 11 days. His analysis also revealed a uniform rainfall zone along the eastern edge of the Wheatbelt from Beacon to Southern Cross to Grass Patch. It identified a weakening of the Indian Ocean Trough to the west of Perth since the mid-1970's which was directly related to the decline in winter rainfall. Dr Stephens said the analysis highlighted that the shift to earlier sowing of winter crops measured recently by AEGIC should continue because early sown crops take advantage of any additional summer soil moisture. "They also experience a lower evaporative demand through the growing season, and are less affected by declining rain in October and rising spring temperatures," he said. In pastoral regions in much of WA, increasing summer rain with a reduction in rainfall variability has assisted perennial C4 (tropical) plants at the expense of C3 (temperate) grasses, especially in the southern areas. "Australia is going to need some of the most water-efficient farming systems in the world to mitigate the effects of a drier and warmer climate in southern Australia,'' Dr Stephens said. "Research in this area is vital because Australian crop yields have been among the most affected by climate change compared to other grain exporting nations."