With increasing global and regional temperatures, even in Switzerland the growing season has lengthened considerably. Using data from the Federal Office of Meteorology and Climatology, Agroscope has traced the development of the growing season since the start of the previous century.
The thermal growing season is the time of year when temperature conditions permit plant growth.
Since 1900, the growing season has increased by around 30 days
A systematic analysis of the spatial temperature data from the Federal Office of Meteorology and Climatology (MeteoSwiss) shows that the growing season has increased by around thirty days since the start of the previous century (Fig. 1), with this trend taking place mainly in the first decades of the 20th century and after 1980. The earlier start and later end to the growing season have also been well documented by observations of phenological events and have already led to adaptations in farming practice, such as an earlier start to the hay harvest.
A longer growing season is associated with higher accumulated temperatures
The increase in available growing days has resulted in a significant rise in accumulated temperatures, i.e. the amount of heat that can be used for plant development (Fig. 2). For arable farming, this has both positive and negative implications. On a positive note, farmers have more options in terms of both the choice of crop and/or variety as well as the selection and establishment of crop rotations. However, rising temperatures lead to accelerated phenological development, which invariably brings forward the time of harvest. This is not necessarily advantageous as it can mean less time for yield establishment.
Favourable zones shifting upwards?
If we plot the duration of the growing season as a function of altitude, as in Figure 1, it is clear that a longer growing season can also be considered as an upward shift. This begs the question as to what extent zones suitable for crop production have already shifted in altitude. In fact, numerous observations confirm an upward shift in the distribution of plants and animals in recent decades. However, in virtually all cases the actual shift is lower than Figure 1 would suggest as other elements apart from temperature also come into play. Specifically, favourable agricultural areas can only evolve when interactions between climate, topography and soil are conducive. Follow-up studies should address the question of what factors are important for growing crops at higher altitude.
- In recent decades the growing season has increased significantly at all elevations. This is also true of the available heat units within the growing season.
- The earlier start and later end to the growing season have already left their mark in forage production (the hay harvest now takes place around 10 days earlier than was the case in 1980) and in arable farming (earlier harvesting dates, e.g. for wheat).
- This trend is set to continue in the future and will require further adaptations to farming practice.
- Rising temperatures and a longer growing season may cause favourable growing areas to shift upwards. However, the extent to which this potential may be realised depends on many other localised factors such as topography and soil.