The prolonged period of bad weather from autumn 2023 to spring 2024 has inevitably led to concerns about the potential impact on crop yields.

It’s useful to put this recent experience in historical perspective. So, it’s worthwhile to look at yield and rainfall developments over the last couple of decades.

There can be few sceptics out there at this stage about the impact of climate change on the sector.

The predictions of wetter winters, drier summers and extreme weather events are unfortunately all too apparent in recent years.

I’ll focus here on the yields of potatoes, spring and winter barley and winter wheat from 2000 to date.

The potato yield has been increasing at an average rate of about 0.5t/ha. Since 2000, yields have fallen significantly below trend in 2008 (-12%), 2009 (-22%), 2012 (-30%), 2018 (-17%) and 2020 (-18%).

In the case of spring barley, the growth in yield has been much more modest at about 70kg/ha. Yield has been well below trend in 2002 (-16%), 2005 (-7%), 2009 (-11%), 2012 (-13%), 2018 (-29%) and 2020 (-8%).

For winter barley, a slightly higher annual trend increase of 90kg/ha is apparent. Yield has been well below trend in 2002 (-14%), 2005 (-7%), 2007 (-7%), 2012 (-10%), 2020 (-13%) and 2022 (-18%).

The annual trend growth in the yield of winter wheat has been about 80kg/ha. In the last two decades or so, significant declines relative to trend are evident in 2009 (-9%), 2012 (-23%), 2018 (-12%) and 2020 (-15%).

For the period examined, it emerges that all the crops considered suffered a serious depression in yields in the years 2012 and 2020. And for 2018, winter barley was the only crop not to experience a poor yield outcome relative to trend.

Weather anomalies and rainfall in particular have undoubtedly accounted for a significant fraction of these yield anomalies. But of course the relationship between yield fluctuations and weather is complex and dependent on location, soil conditions, season, crop type and temperature. But it’s still instructive to look at the prevailing rainfall anomalies since 2000.

Fortunately, we have an excellent set of annual and seasonal rainfall data stretching back to 1850, which has been assembled by Prof Conor Murphy and his colleagues at Maynooth University.

For winter rainfall, 2016 and 2014 were record high years

Among the many fascinating insights of this data is the revelation that the years 2023, 2016, 2011 and 2005 had the highest annual rainfall going back to 1850.

For winter rainfall, 2016 and 2014 were record high years over the same period.

No year in the last two decades or so stands out over the period since 1850 for either spring or summer rainfall. But, in the case of autumn rainfall, 2022 and 2000 exhibit historic high figures.

In four of the five years of exceptional negative potato yields since 2000, rainfall in summer exceeded its 30-year average; ranging from +38% to +62%.

In four of the six years of anomalous spring barley yields, rainfall in both spring and summer was also exceptionally high with a range in spring from +11% to +30% and in summer from 5% to +62%.

For winter barley, in four out of the six poor yield years, summer rainfall was anomalous with a range from +5% to +62%. And for three of the four years of poorly performing winter summer rainfall was deviant with a range from +38% to +62%.

Poor weather is unfortunately a systemic risk of farming.

Gerry Boyle of Teagasc. \ Dave Ruffles