Dry summers can see a loss of up to 25% of total Swiss roughage production. This is because grassland yields are strongly correlated with summer drought, as shown by a new analysis conducted by Agroscope and the Swiss Farmers’ Union.
Swiss grassland covers a substantial proportion of domestic feed demand. In recent decades, the growth of meadows and pastures has often been adversely affected by water scarcity during the summer months. A better understanding of the effects of summer drought on Swiss grassland productivity can help the agricultural sector to prepare for future challenges.
We investigated the extent to which summer drought accounted for the roughage yields for the years 1990 to 2021 according to the calculations of the Swiss Farmers’ Union. The extent of the summer drought was assessed by measuring relative evaporation, an internationally used benchmark for crop water requirement, based on the spatial climate analyses of the Federal Office for Meteorology and Climatology. We grouped our results into the three grassland categories of temporary leys, meadows and pastures outside of the summer grazing areas as well as summer-grazing pastures.
Strong impact of drought on grassland yields
The results show that for all three grassland categories, summer drought accounts for 50 to 60% of the fluctuations in yield. Furthermore, persistent water shortages during the summer months can cause yield losses of around 30 to 40% in extreme years. Distinct productivity shortfalls at national scale occurred in 1998, 2003, 2006, 2015 and 2018 in particular.
With a total Swiss production of around 5.5 million tonnes dry matter per annum, production losses of up to 1.2 million tonnes dry matter (compared to the long-term average) are possible in unfavourable years. This is far more than the approx. 250,000 tonnes of feed imported in a year like 2018. These figures underscore the vulnerability of feed production to extreme climate events.
Temporary leys hit hardest
Temporary leys as well as meadows and pastures below 1000 to 1500m above sea level are particularly affected by summer drought. With temporary leys in particular, water shortages cause steep declines in productivity. On the one hand, this could be due to the fact that, as part of the rotation, temporary leys must always be created afresh, and in the first year do not possess a fully developed root system which would cushion against temporary water scarcity. On the other hand, temporary leys are almost exclusively found in the low altitudes of the Swiss Central Plateau, where the dynamic and intensity of drought periods has been strongest in the past.
In addition, maps of the spatial distribution of drought reveal regional differences caused by the dissimilar weather patterns. Whereas in 1998 only West Switzerland and in 2003 Northwest Switzerland as well as the area between Lake Neuchâtel and Lake Geneva had to contend with extreme drought, in 2015 and 2018 much of the Central Plateau and part of the Canton of Grisons were affected.
- Relative evaporation, a measure of crop water requirement, can be used to investigate the effects of summer drought on Swiss grassland yields and to identify spatial patterns.
- Summer drought alone accounts for up to 60% of the fluctuations in average grassland yields observed in Switzerland between 1990 and 2021.
- In extreme years, yield losses of around 30 to 40% at the national level are possible.
- Given a possible future increase in extreme drought conditions, the results underscore the necessity of adaptive measures.