Jeff Hoffmann
'Ceranya'
Lockhart NSW

Re-living the last 112 years through the study of rainfall records helped Jeff Hoffman develop a solid body of climate knowledge that he uses to plan his crops.

 

Jeff, his wife Larraine and their son Oliver run 'Ceranya' at Lockhart in the NSW wheatbelt, with an average rainfall of 470mm. The property is an 1100 hectare mixed enterprise, producing canola, wheat, pulses, merino sheep and cattle. In the mid-eighties Jeff heard that there were local rainfall records going back over 100 years. He got copies of the records and worked out how he could turn them into something more useful than a pile of paper. 'I started by manually sorting the records into deciles and plotting probability charts for monthly and annual rainfall' said Jeff. 'I calculated the real average rainfall for the area, which is 50mm below what is commonly believed. 'I kept looking at each month and each season to try to find better ways of understanding the rainfall.' The next step was working out the timing of the Autumn break, an important factor in sowing and fertilising crops. Jeff found it difficult to find any objective way of even defining the Autumn break. 'Eventually I defined it subjectively by saying it was enough rain to germinate the winter pasture and allow it to survive' said Jeff.

Under this definition, Jeff worked through the rainfall records and found that the break normally happened at the end of April or early May. But there was one year in ten when it didn't break till June. This led him to question the idea of a 'normal' year.

'You can't say something is abnormal if you can expect it every tenth year' said Jeff.

'I started to look at the ways that farmers, politicians and meteorologists define drought. There is a level of climate risk that a farmer must expect to make provision for. I believe that abnormal would not occur any more than five times in 100 years. Anything more than that should probably be regarded as a normal climate variation.'

Jeff's work became a little easier with the acquisition of a computer. He took the huge step of typing the historic rainfall records into the spreadsheet program Excel. What could have been a long and tedious task instead became a fascinating re-living of every season.

'I was like the farmers themselves - I didn't know what was coming because I'd just be typing in each figure as I got up to it. So as I was going through a particular year I'd be experiencing how the rain came. Oh it's dry. Now we have a shower of rain. Gee, another dry patch. We've had the pasture and we're losing it. Nine points comes down, it just might save the day. Then 16 points a couple of days later and half an inch a couple of days after that. We're OK.

'I knew what that would mean to the farmers who were going out and recording the rain. So I found myself living these seasons in my mind as I typed them in. While I can't easily present that information, it helped me understand' said Jeff.

Jeff graphed out the accumulated deviation from the mean over the hundred-year period. This shows how rainfall patterns vary in the long term and it showed him that there were significant periods, of 10-20 years in length, when things were very different from the overall trend.

'This area was originally settled by Germans from South Australia' said Jeff. 'They had a period from 1880s to the turn of the century when it was significantly wetter than the mean. These guys came over, selected the land, cleared it and planted crops, even vineyards. Year after year it seemed to be working.'

'Then there was a very long period, up to nearly 1920, when there were dryer than average seasons.

'You can see what that would have done to your impressions of what you could do on this farm. In those times of long wetter trends, they'd be optimistic. In the long dryer trends they'd be pessimistic. In the times when it was around average they'd be realistic. I started farming in a dry trend in the late 1960s, so I tend to be pessimistic.'

After the 1994 drought Jeff began using a number of software packages to help manage his farm, including Rainman. By this time he was developing a far greater understanding of how the Southern Oscillation Index influenced the local area.

'The end of July is a critical time for fertiliser on crops. I found that on average if the SOI at that time was less than ten and falling then the average rainfall for spring was 112mm. If the SOI was plus ten and rising then the average rainfall for spring was 226mm' said Jeff.

'What it meant for this area was that significant differences in rainfall could be predicted by the SOI. The same sort of differences showed up in our crop yields.

'In 1997 I analysed the SOI with the help of Rainman and used the probability of having a low spring rainfall to make the decision not to apply nitrogen fertiliser and to sell stock early. These turned out to be good decisions.

'The SOI was low in June and July. The ground was dry, there was no sub-soil moisture. So I decided not to put out nitrogen fertiliser to the crops. The spring fizzled out and yields were quite low.

'Applying fertliser would have given me even lower yields because it would have enouraged the crops to grow and use more water and they would have yielded even less.'

In response to increasing questions from other farmers, Jeff spent time in 1996 setting out the historic rainfall record and the SOI values for winter in a way that they could easily understand. He also used his bank of rainfall data to work out the yields he could feasibly aim for over the longer term.

'By applying a simple model over all the available rainfall data I could see the average and the range of yields which might be achievable' said Jeff.

'I have enough experience to evaluate the model and assess the risks in targeting high yields, as against lost opportunities by setting targets which are too conservative. I was targeting yields of three tonnes per hectare a few years back. I am now targeting four.

'There would be people setting higher targets than that and achieving them at times. The difference is that I have a sound basis for my target.'

In spite of his hard work, Jeff is cautious about what can be expected from applying climate information to farming.

'At the end of the day, all the work doesn't tell me if rain will happen or not' he said. 'Knowledge should increase the chances of being right, but I think that predicting anything is difficult. Especially the future!

'There are still a lot of good rainfall years when the SOI is low and falling. You can be conservative and sell all the stock and not put any fertiliser on and you might end up having a good year.

'That kind of decision could end up costing you more money than an actual drought!

'You have to remember that climate is all about probabilities, not certainties. Farming is about minimising risk. There are very small margins for error in crop and livestock production. Not understanding the climate can increase the risk.

'There are other factors that will increase our understanding of the climate, such as sea surface temperatures. I believe our knowledge will increase rapidly from this time on.

'I have not mastered the climate, but my farm enterprise has benefited' said Jeff. 'The climate is the only factor we have no control over and our only way of working with it is to understand it well.'