Crops yield to climate change

We are already seeing the impact of climate change in the range and yields of crops grown in Europe. In Northern Europe we can now grow more heat-demanding crops, while Southern Europe increasingly suffers from droughts and heat waves.

For a long time climate change was only a prediction for sometime in the future. But now the future is here. The impact of the changes can already be felt in agriculture.

Climate change means more than just a rise in temperature. In some areas crops will thirst for water, while in others they will drown in heavy downpours. And while some agricultural crops will benefit from changes that include a warmer climate, altered precipitation patterns and a rise in atmospheric CO2 levels, the changes are definitely not a blessing for agriculture everywhere.

A group of scientists in the COST 734 research network carried out a survey in 2008. They asked experts in a number of European countries what their expectations were in terms of the effect of climate change on crops by year 2050. The expectations were not favourable everywhere.

- The most negative effects are expected in the Eastern European countries Hungary, Serbia, Bulgaria and Rumania. This area will suffer from more frequent droughts and heat waves without being able to adapt, by – for example – seasonally adjusting the crop management, says research professor Jørgen E. Olesen from the Faculty of Agricultural Sciences, who was responsible for the survey.

The range of expected effects – both positive and negative – was otherwise equally large in Northern Europe as in Southern Europe. There were, however, large differences in what was deemed positive and negative in the different regions.

- It really depends on how well you can adapt to the climate changes in order to maintain yields. There are a number of ways you can adjust the cropping system to lessen the negative impact of climate change and exploit the positive effects, explains Jørgen E. Olesen.

When all the effects of climate change are included, such as yield, pesticide use, nutrient losses, water consumption, etc., the questionnaire-based study reveals that in most of Europe the effects are unfortunately mainly going to be negative.

Hot and dry in Southern Europe

The problem is man-made. We emit billions of tonnes of greenhouse gases that contribute to global warming. The emissions are on the rise and over this century they are expected to lead to a rise in the global mean temperature of between 1.4 and 5.8°C.

In Europe the largest temperature rises are expected in Eastern Europe over the winter period. In the western and southern part of Europe, the temperature will rise mainly during the summer months.

- Large temperature rises are predicted for Southwestern Europe during the summer period, with average mean temperature increases of 6°C in parts of Spain and France, warns Jørgen E. Olesen.

It is likely that the frequency, severity and duration of droughts will increase in the future, particularly in Southern and Central Europe. Heat waves and droughts like the one in France in 2003 may become commonplace towards the end of the century. The heat wave in 2003 led to large agricultural and economic losses in the affected areas.

Europe has not only experienced considerable temperature rises in recent decades. There is also more variability in the temperature with a clear tendency for more frequent heat waves.

Rainfall patterns have also changed, with, for example, more frequent droughts in spring and early summer, particularly in Southern and Eastern Europe. Annual rainfall has increased in Western and Northern Europe, while it has decreased in the Mediterranean basin. Throughout Europe there has been a rise in extreme precipitation events, even in areas that have become drier. This has sometimes led to severe flooding during the summer period.

In Southern Europe the higher frequency of heat waves and droughts has led to a higher incidence of crop failure. Yields are also seen to be more variable between years. Much of this is due to climate changes, where reduced rainfall also means that there is less water available for irrigation.

Cropping practices change

The situation is not completely hopeless, as agriculture to a certain extent has been able to adapt to the new situation. The changes in the climate have already resulted in changes in management practices in Europe. The growing of warm-season crops such as maize and wine has spread northwards. In Belgium, grain maize now comprises about 20% of the cereal cropping area against virtually none 20 years ago. In general, the basis for production has been strengthened in Northern Europe.

The environment influences agricultural production via effects on plants, animal and soil. The anthropogenic emissions of greenhouse gases affect plants, animal and soil both directly (particularly through CO2 effects) and indirectly through changes in climate (particularly temperature and precipitation). The exact effects vary considerably between different cropping systems and also depend on the changes in individual determining factors relative to each other. There can also be large regional variations within Europe.

Crop yield depends in the main on three factors: 1) the length of the active growing season, 2) the daily production during the growing season, and 3) the proportion of the dry matter production that ends up in the harvestable part. All these factors vary between crops and are also affected by climate change.

An increased atmospheric CO2 concentration will improve yield in most crops (maize being the exception). For crops that do not grow to maturity (grass and sugar beet, for example), a higher temperature will expand the growing season and thus result in higher yields, if water is not a limiting factor.

In annual agricultural crops such as cereal, rapeseed and potato, plant development depends on temperature and the number of daylight hours. A rise in temperature will reduce the duration of the active growing period for these crops because the crops will mature earlier. This will in effect reduce yield.

The yield reduction is larger in winter crops than in spring crops where it is possible to offset some of the effect by sowing the crop earlier, thus enabling it to utilise the favourable light conditions in the spring. Increased yields will mainly be achieved by changing to new crop species and varieties.