Extreme weather

20 Aug 2015

There was some interesting weather in the UK in July. The 1st was the hottest July day on record and a temperature of only 10C was recorded in Powys on the 31st. However, the extreme event of note for me was the overnight thunderstorm on 16th/17th in Cambridge. Up to that point, I was desperate for rain in order to perk up our garden and allotment. We had had rain forecast several times but received tiny amounts, if any at all. As they say in Norfolk, “it never rains in a dry time”.

Unfortunately we were away when the thunderstorm occurred and so I did not experience it at firsthand. The first I knew of it was when I checked the online weather station in Cambridge the following morning (I was that desperate for rain!). It said that there had been a total of over 50mm of rain overnight. When we got back on the 18th, I cycled up to the allotment where my rain gauge had recorded 80mm of rain. Up to 90mm was recorded locally. It must have been an amazing storm to witness.

This got me thinking about the challenges from weather events to our crops and their management. The dull and wet summer of 2012 was one such seasonal extreme event. It took a large toll on wheat yields in some parts of England, particularly on the heavy clays. I also clearly recall the dry and hot summer of 1976 (it was actually very dry from June 1975 to September 1976). It is not just the extreme summer weather events that can impact on our wheat crop; the wet autumn and winter of 2000 reduced the yields achieved in 2001. However, despite what we sometimes consider to be extreme weather variations, UK wheat yields are amazingly consistent from year to year when compared to some other parts of the world.

One notable example of large variations in yield over the years is in parts of Australia. There is an area in Victoria, north of Bendigo, called the Mallee, which is perhaps close to being marginal for arable crop production. Harm van Rees, a leading Australian agronomist, recently sent me the following data on its growing-season rainfall (GSR) expressed as deviation from average (rather than ‘of average’ as stated on the y-axis). As you can see, there have been a very high number of dry seasons over the last 15 years or so and the ten year running mean (the red line) is still going down. In the very dry seasons, wheat yields can be alarmingly low (often below 1.0 t/ha) or zero and many farms are in financial crisis. There was a similar but shorter downward trend of the ten year running mean in the 1940s. The anxiety about the current trend is heightened because of the concern over the possible influence that climate change may have been having on the rainfall in recent years and may have in the future.

So what would you do in this situation? Not an easy question to answer. Australian researchers have developed sophisticated risk management tools for use in arable farming, many of which are now based on seasonal forecasts. For instance, these help to decide on how much nitrogen to use as applying any nitrogen in a very dry year can reduce wheat yields as well as unnecessarily increase costs. A preliminary analysis suggests these tools are beneficial when compared to adopting the same management each year. As one researcher points out “the [seasonal] forecasts are too good to ignore, but not good enough to completely rely on. Even though there are uncertainties, we do have more information than if we were guessing by chance.” However, what farmers and bank managers in the area featured in the rainfall graph really need is a reliable forecast of rainfall not just for the season but also for the next few years.

A recently published report called Extreme Weather and Resilience of the Global Food System warns that major “shocks” to global food production will be three times more likely within 25 years because of an increase in extreme weather brought about by global warming. So we will have to accept that there are going to be even more challenges in the future. Achieving more resilience in our production systems to extreme weather events will have to be given a higher priority. It does not help the UK industry that pesticide resistance and legislation are together impacting on the resilience of our arable systems. It is also regrettable to have to say that opposition to GM may well reduce our ability to respond to the challenges of the future. The report can be found on http://www.foodsecurity.ac.uk/assets/pdfs/extreme-weather-resilience-of-...